Allow more than one field of a syscall trace event to read user space.
Build on top of the user_mask by allowing more than one bit to be set that
corresponds to the @args array of the syscall metadata. For each argument
in the @args array that is to be read, it will have a dynamic array/string
field associated to it.
Note that multiple fields to be read from user space is not supported if
the user_arg_size field is set in the syscall metada. That field can only
be used if only one field is being read from user space as that field is a
number representing the size field of the syscall event that holds the
size of the data to read from user space. It becomes ambiguous if the
system call reads more than one field. Currently this is not an issue.
If a syscall event happens to enable two events to read user space and
sets the user_arg_size field, it will trigger a warning at boot and the
user_arg_size field will be cleared.
The per CPU buffer that is used to read the user space addresses is now
broken up into 3 sections, each of 168 bytes. The reason for 168 is that
it is the biggest portion of 512 bytes divided by 3 that is 8 byte aligned.
The max amount copied into the ring buffer from user space is now only 128
bytes, which is plenty. When reading user space, it still reads 167
(168-1) bytes and uses the remaining to know if it should append the extra
"..." to the end or not.
This will allow the event to look like this:
sys_renameat2(olddfd: 0xffffff9c, oldname: 0x7ffe02facdff "/tmp/x", newdfd: 0xffffff9c, newname: 0x7ffe02face06 "/tmp/y", flags: 1)
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Takaya Saeki <takayas@google.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ian Rogers <irogers@google.com>
Cc: Douglas Raillard <douglas.raillard@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/20251028231148.095789277@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
As of commit 654ced4a13 ("tracing: Introduce tracepoint_is_faultable()")
system call trace events allow faulting in user space memory. Have some of
the system call trace events take advantage of this.
Use the trace_user_fault_read() logic to read the user space buffer from
user space and instead of just saving the pointer to the buffer in the
system call event, also save the string that is passed in.
The syscall event has its nb_args shorten from an int to a short (where
even u8 is plenty big enough) and the freed two bytes are used for
"user_mask". The new "user_mask" field is used to store the index of the
"args" field array that has the address to read from user space. This
value is set to 0 if the system call event does not need to read user
space for a field. This mask can be used to know if the event may fault or
not. Only one bit set in user_mask is supported at this time.
This allows the output to look like this:
sys_access(filename: 0x7f8c55368470 "/etc/ld.so.preload", mode: 4)
sys_execve(filename: 0x564ebcf5a6b8 "/usr/bin/emacs", argv: 0x7fff357c0300, envp: 0x564ebc4a4820)
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Takaya Saeki <takayas@google.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ian Rogers <irogers@google.com>
Cc: Douglas Raillard <douglas.raillard@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/20251028231147.261867956@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
The write to the trace_marker file is a critical section where it cannot
take locks nor allocate memory. To read from user space, it allocates a per
CPU buffer when the trace_marker file is opened, and then when the write
system call is performed, it uses the following method to read from user
space:
preempt_disable();
buffer = per_cpu_ptr(cpu_buffers, cpu);
do {
cnt = nr_context_switches_cpu();
migrate_disable();
preempt_enable();
ret = copy_from_user(buffer, ptr, len);
preempt_disable();
migrate_enable();
} while (!ret && cnt != nr_context_switches_cpu());
if (!ret)
ring_buffer_write(buffer);
preempt_enable();
It records the number of context switches for the current CPU, enables
preemption, copies from user space, disable preemption and then checks if
the number of context switches changed. If it did not, then the buffer is
valid, otherwise the buffer may have been corrupted and the read from user
space must be tried again.
The system call trace events are now faultable and have the same
restrictions as the trace_marker write. For system calls to read the user
space buffer (for example to read the file of the openat system call), it
needs the same logic. Instead of copying the code over to the system call
trace events, make the code generic to allow the system call trace events to
use the same code. The following API is added internally to the tracing sub
system (these are only exposed within the tracing subsystem and not to be
used outside of it):
trace_user_fault_init() - initializes a trace_user_buf_info descriptor
that will allocate the per CPU buffers to copy from user space into.
trace_user_fault_destroy() - used to free the allocations made by
trace_user_fault_init().
trace_user_fault_get() - update the ref count of the info descriptor to
allow more than one user to use the same descriptor.
trace_user_fault_put() - decrement the ref count.
trace_user_fault_read() - performs the above action to read user space
into the per CPU buffer. The preempt_disable() is expected before
calling this function and preemption must remain disabled while the
buffer returned is in use.
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Takaya Saeki <takayas@google.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ian Rogers <irogers@google.com>
Cc: Douglas Raillard <douglas.raillard@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/20251028231147.096570057@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
The ftrace blktrace path allocates buffers and writes trace events but
was using the wrong recording function. After
commit 4d8bc7bd4f ("blktrace: move ftrace blk_io_tracer to blk_io_trace2"),
the ftrace interface was moved to use blk_io_trace2 format, but
__blk_add_trace() still called record_blktrace_event() which writes in
blk_io_trace (v1) format.
This causes critical data corruption:
- blk_io_trace (v1) has 32-bit 'action' field at offset 28
- blk_io_trace2 (v2) has 32-bit 'pid' at offset 28 and 64-bit 'action'
at offset 32
- When record_blktrace_event() writes to a v2 buffer:
* Writing pid (offset 32 in v1) corrupts the v2 action field
* Writing action (offset 28 in v1) corrupts the v2 pid field
* The 64-bit action is truncated to 32-bit via lower_32_bits()
Fix by:
1. Adding version switch to select correct format (v1 vs v2)
2. Calling appropriate recording function based on version
3. Defaulting to v2 for ftrace (as intended by commit 4d8bc7bd4f)
4. Adding WARN_ONCE for unexpected version values
Without this patch :-
linux-block (for-next) # sh reproduce_blktrace_bug.sh
dd-14242 [033] d..1. 3903.022308: Unknown action 36a2
dd-14242 [033] d..1. 3903.022333: Unknown action 36a2
dd-14242 [033] d..1. 3903.022365: Unknown action 36a2
dd-14242 [033] d..1. 3903.022366: Unknown action 36a2
dd-14242 [033] d..1. 3903.022369: Unknown action 36a2
The action field is corrupted because:
- ftrace allocated blk_io_trace2 buffer (64 bytes)
- But called record_blktrace_event() (writes v1, 48 bytes)
- Field offsets don't match, causing corruption
The hex value shown 0x30e3 is actually a PID, not an action code!
linux-block (for-next) #
linux-block (for-next) #
linux-block (for-next) # sh reproduce_blktrace_bug.sh
Trace output looks correct:
dd-2420 [019] d..1. 59.641742: 251,0 Q RS 0 + 8 [dd]
dd-2420 [019] d..1. 59.641775: 251,0 G RS 0 + 8 [dd]
dd-2420 [019] d..1. 59.641784: 251,0 P N [dd]
dd-2420 [019] d..1. 59.641785: 251,0 U N [dd] 1
dd-2420 [019] d..1. 59.641788: 251,0 D RS 0 + 8 [dd]
Fixes: 4d8bc7bd4f ("blktrace: move ftrace blk_io_tracer to blk_io_trace2")
Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The WARN_ON_ONCE introduced in
commit f9ee38bbf7 ("blktrace: add block trace commands for zone operations")
triggers kernel warnings when zone operations are traced with blktrace
version 1. This can spam the kernel log during normal operation with
zoned block devices when userspace is using the legacy blktrace
protocol.
Currently blktrace implementation drops newly added REQ_OP_ZONE_XXX
when blktrace userspce version is set to 1.
Remove the WARN_ON_ONCE and quietly filter these events. Add a
rate-limited debug message to help diagnose potential issues without
flooding the kernel log. The debug message can be enabled via dynamic
debug when needed for troubleshooting.
This approach is more appropriate as encountering zone operations with
blktrace v1 is an expected condition that should be handled gracefully
rather than warned about, since users may be running older blktrace
userspace tools that only support version 1 of the protocol.
With this patch :-
linux-block (for-next) # git log -1
commit c8966006a0971d2b4bf94c0426eb7e4407c6853f (HEAD -> for-next)
Author: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
Date: Mon Oct 27 19:26:53 2025 -0700
blktrace: use debug print to report dropped events
linux-block (for-next) # cdblktests
blktests (master) # ./check blktrace
blktrace/001 (blktrace zone management command tracing) [passed]
runtime 3.805s ... 3.889s
blktests (master) # dmesg -c
blktests (master) # echo "file kernel/trace/blktrace.c +p" > /sys/kernel/debug/dynamic_debug/control
blktests (master) # ./check blktrace
blktrace/001 (blktrace zone management command tracing) [passed]
runtime 3.889s ... 3.881s
blktests (master) # dmesg -c
[ 77.826237] blktrace: blktrace v1 cannot trace zone operation 0x1000190001
[ 77.826260] blktrace: blktrace v1 cannot trace zone operation 0x1000190004
[ 77.826282] blktrace: blktrace v1 cannot trace zone operation 0x1001490007
[ 77.826288] blktrace: blktrace v1 cannot trace zone operation 0x1001890008
[ 77.826343] blktrace: blktrace v1 cannot trace zone operation 0x1000190001
[ 77.826347] blktrace: blktrace v1 cannot trace zone operation 0x1000190004
[ 77.826350] blktrace: blktrace v1 cannot trace zone operation 0x1001490007
[ 77.826354] blktrace: blktrace v1 cannot trace zone operation 0x1001890008
[ 77.826373] blktrace: blktrace v1 cannot trace zone operation 0x1000190001
[ 77.826377] blktrace: blktrace v1 cannot trace zone operation 0x1000190004
blktests (master) # echo "file kernel/trace/blktrace.c -p" > /sys/kernel/debug/dynamic_debug/control
blktests (master) # ./check blktrace
blktrace/001 (blktrace zone management command tracing) [passed]
runtime 3.881s ... 3.824s
blktests (master) # dmesg -c
blktests (master) #
Reported-by: syzbot+153e64c0aa875d7e4c37@syzkaller.appspotmail.com
Fixes: f9ee38bbf7 ("blktrace: add block trace commands for zone operations")
Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Dynptr currently caps size and offset at 24 bits, which isn’t sufficient
for file-backed use cases; even 32 bits can be limiting. Refactor dynptr
helpers/kfuncs to use 64-bit size and offset, ensuring consistency
across the APIs.
This change does not affect internals of xdp, skb or other dynptrs,
which continue to behave as before. Also it does not break binary
compatibility.
The widening enables large-file access support via dynptr, implemented
in the next patches.
Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251026203853.135105-3-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Trace zone write plugging operations on block devices.
As tracing of zoned block commands needs the upper 32bit of the widened
64bit action, only add traces to blktrace if user-space has requested
version 2 of the blktrace protocol.
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Expose ZONE APPEND completions as a block trace completion action to
blktrace.
As tracing of zoned block commands needs the upper 32bit of the widened
64bit action, only add traces to blktrace if user-space has requested
version 2 of the blktrace protocol.
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Add block trace commands for zone operations. These commands can only be
handled with version 2 of the blktrace protocol. For version 1, warn if a
command that does not fit into the 16 bits reserved for the command in
this version is passed in.
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Differentiate between blk_io_trace and blk_io_trace2 when relaying to
user-space depending on which version has been requested by the blktrace
utility.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Add definitions for the extended version of the blktrace protocol using a
wider action type to be able to record new actions in the kernel.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Pass struct blk_user_trace_setup2 to blktrace_setup_finalize(). This
prepares for the incoming extension of the blktrace protocol with a 64bit
act_mask.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Add definitions for a version 2 of the blk_user_trace_setup ioctl. This
new ioctl will enable a different struct layout of the binary data passed
to user-space when using a new version of the blktrace utility requesting
the new struct layout.
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Split do_blk_trace_setup into two functions, this is done to prepare for
an incoming new BLKTRACESETUP2 ioctl(2) which can receive extended
parameters from user-space.
Also move the size verification logic to the callers in preparation for
using a new internal structure later.
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Change the internal use of the action in blktrace to 64bit. Although for
now only the lower 32bits will be used.
With the upcoming version 2 of the blktrace user-space protocol the upper
32bit will also be utilized.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Untangle the if/else sequence setting the trace action in
__blk_add_trace() and turn it into a switch statement for better
extensibility.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Split out the code relaying a blktrace event to user-space using relayfs.
This enables adding a second version supporting a new version of the
protocol.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Factor out the recording of a blktrace event into its own function,
deduplicating the code.
This also enables recording different versions of the blktrace protocol
later on.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
De-duplicate the calculation of the trace length instead of doing the
calculation twice, once for calling trace_buffer_lock_reserve() and once
for calling relay_reserve().
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Pull tracing fixes from Steven Rostedt:
"The previous fix to trace_marker required updating trace_marker_raw as
well. The difference between trace_marker_raw from trace_marker is
that the raw version is for applications to write binary structures
directly into the ring buffer instead of writing ASCII strings. This
is for applications that will read the raw data from the ring buffer
and get the data structures directly. It's a bit quicker than using
the ASCII version.
Unfortunately, it appears that our test suite has several tests that
test writes to the trace_marker file, but lacks any tests to the
trace_marker_raw file (this needs to be remedied). Two issues came
about the update to the trace_marker_raw file that syzbot found:
- Fix tracing_mark_raw_write() to use per CPU buffer
The fix to use the per CPU buffer to copy from user space was
needed for both the trace_maker and trace_maker_raw file.
The fix for reading from user space into per CPU buffers properly
fixed the trace_marker write function, but the trace_marker_raw
file wasn't fixed properly. The user space data was correctly
written into the per CPU buffer, but the code that wrote into the
ring buffer still used the user space pointer and not the per CPU
buffer that had the user space data already written.
- Stop the fortify string warning from writing into trace_marker_raw
After converting the copy_from_user_nofault() into a memcpy(),
another issue appeared. As writes to the trace_marker_raw expects
binary data, the first entry is a 4 byte identifier. The entry
structure is defined as:
struct {
struct trace_entry ent;
int id;
char buf[];
};
The size of this structure is reserved on the ring buffer with:
size = sizeof(*entry) + cnt;
Then it is copied from the buffer into the ring buffer with:
memcpy(&entry->id, buf, cnt);
This use to be a copy_from_user_nofault(), but now converting it to
a memcpy() triggers the fortify-string code, and causes a warning.
The allocated space is actually more than what is copied, as the
cnt used also includes the entry->id portion. Allocating
sizeof(*entry) plus cnt is actually allocating 4 bytes more than
what is needed.
Change the size function to:
size = struct_size(entry, buf, cnt - sizeof(entry->id));
And update the memcpy() to unsafe_memcpy()"
* tag 'trace-v6.18-3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Stop fortify-string from warning in tracing_mark_raw_write()
tracing: Fix tracing_mark_raw_write() to use buf and not ubuf
The fix to use a per CPU buffer to read user space tested only the writes
to trace_marker. But it appears that the selftests are missing tests to
the trace_maker_raw file. The trace_maker_raw file is used by applications
that writes data structures and not strings into the file, and the tools
read the raw ring buffer to process the structures it writes.
The fix that reads the per CPU buffers passes the new per CPU buffer to
the trace_marker file writes, but the update to the trace_marker_raw write
read the data from user space into the per CPU buffer, but then still used
then passed the user space address to the function that records the data.
Pass in the per CPU buffer and not the user space address.
TODO: Add a test to better test trace_marker_raw.
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/20251011035243.386098147@kernel.org
Fixes: 64cf7d058a ("tracing: Have trace_marker use per-cpu data to read user space")
Reported-by: syzbot+9a2ede1643175f350105@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/68e973f5.050a0220.1186a4.0010.GAE@google.com/
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Pull tracing clean up and fixes from Steven Rostedt:
- Have osnoise tracer use memdup_user_nul()
The function osnoise_cpus_write() open codes a kmalloc() and then a
copy_from_user() and then adds a nul byte at the end which is the
same as simply using memdup_user_nul().
- Fix wakeup and irq tracers when failing to acquire calltime
When the wakeup and irq tracers use the function graph tracer for
tracing function times, it saves a timestamp into the fgraph shadow
stack. It is possible that this could fail to be stored. If that
happens, it exits the routine early. These functions also disable
nesting of the operations by incremeting the data "disable" counter.
But if the calltime exits out early, it never increments the counter
back to what it needs to be.
Since there's only a couple of lines of code that does work after
acquiring the calltime, instead of exiting out early, reverse the if
statement to be true if calltime is acquired, and place the code that
is to be done within that if block. The clean up will always be done
after that.
- Fix ring_buffer_map() return value on failure of __rb_map_vma()
If __rb_map_vma() fails in ring_buffer_map(), it does not return an
error. This means the caller will be working against a bad vma
mapping. Have ring_buffer_map() return an error when __rb_map_vma()
fails.
- Fix regression of writing to the trace_marker file
A bug fix was made to change __copy_from_user_inatomic() to
copy_from_user_nofault() in the trace_marker write function. The
trace_marker file is used by applications to write into it (usually
with a file descriptor opened at the start of the program) to record
into the tracing system. It's usually used in critical sections so
the write to trace_marker is highly optimized.
The reason for copying in an atomic section is that the write
reserves space on the ring buffer and then writes directly into it.
After it writes, it commits the event. The time between reserve and
commit must have preemption disabled.
The trace marker write does not have any locking nor can it allocate
due to the nature of it being a critical path.
Unfortunately, converting __copy_from_user_inatomic() to
copy_from_user_nofault() caused a regression in Android. Now all the
writes from its applications trigger the fault that is rejected by
the _nofault() version that wasn't rejected by the _inatomic()
version. Instead of getting data, it now just gets a trace buffer
filled with:
tracing_mark_write: <faulted>
To fix this, on opening of the trace_marker file, allocate per CPU
buffers that can be used by the write call. Then when entering the
write call, do the following:
preempt_disable();
cpu = smp_processor_id();
buffer = per_cpu_ptr(cpu_buffers, cpu);
do {
cnt = nr_context_switches_cpu(cpu);
migrate_disable();
preempt_enable();
ret = copy_from_user(buffer, ptr, size);
preempt_disable();
migrate_enable();
} while (!ret && cnt != nr_context_switches_cpu(cpu));
if (!ret)
ring_buffer_write(buffer);
preempt_enable();
This works similarly to seqcount. As it must enabled preemption to do
a copy_from_user() into a per CPU buffer, if it gets preempted, the
buffer could be corrupted by another task.
To handle this, read the number of context switches of the current
CPU, disable migration, enable preemption, copy the data from user
space, then immediately disable preemption again. If the number of
context switches is the same, the buffer is still valid. Otherwise it
must be assumed that the buffer may have been corrupted and it needs
to try again.
Now the trace_marker write can get the user data even if it has to
fault it in, and still not grab any locks of its own.
* tag 'trace-v6.18-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Have trace_marker use per-cpu data to read user space
ring buffer: Propagate __rb_map_vma return value to caller
tracing: Fix irqoff tracers on failure of acquiring calltime
tracing: Fix wakeup tracers on failure of acquiring calltime
tracing/osnoise: Replace kmalloc + copy_from_user with memdup_user_nul
It was reported that using __copy_from_user_inatomic() can actually
schedule. Which is bad when preemption is disabled. Even though there's
logic to check in_atomic() is set, but this is a nop when the kernel is
configured with PREEMPT_NONE. This is due to page faulting and the code
could schedule with preemption disabled.
Link: https://lore.kernel.org/all/20250819105152.2766363-1-luogengkun@huaweicloud.com/
The solution was to change the __copy_from_user_inatomic() to
copy_from_user_nofault(). But then it was reported that this caused a
regression in Android. There's several applications writing into
trace_marker() in Android, but now instead of showing the expected data,
it is showing:
tracing_mark_write: <faulted>
After reverting the conversion to copy_from_user_nofault(), Android was
able to get the data again.
Writes to the trace_marker is a way to efficiently and quickly enter data
into the Linux tracing buffer. It takes no locks and was designed to be as
non-intrusive as possible. This means it cannot allocate memory, and must
use pre-allocated data.
A method that is actively being worked on to have faultable system call
tracepoints read user space data is to allocate per CPU buffers, and use
them in the callback. The method uses a technique similar to seqcount.
That is something like this:
preempt_disable();
cpu = smp_processor_id();
buffer = this_cpu_ptr(&pre_allocated_cpu_buffers, cpu);
do {
cnt = nr_context_switches_cpu(cpu);
migrate_disable();
preempt_enable();
ret = copy_from_user(buffer, ptr, size);
preempt_disable();
migrate_enable();
} while (!ret && cnt != nr_context_switches_cpu(cpu));
if (!ret)
ring_buffer_write(buffer);
preempt_enable();
It's a little more involved than that, but the above is the basic logic.
The idea is to acquire the current CPU buffer, disable migration, and then
enable preemption. At this moment, it can safely use copy_from_user().
After reading the data from user space, it disables preemption again. It
then checks to see if there was any new scheduling on this CPU. If there
was, it must assume that the buffer was corrupted by another task. If
there wasn't, then the buffer is still valid as only tasks in preemptable
context can write to this buffer and only those that are running on the
CPU.
By using this method, where trace_marker open allocates the per CPU
buffers, trace_marker writes can access user space and even fault it in,
without having to allocate or take any locks of its own.
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Luo Gengkun <luogengkun@huaweicloud.com>
Cc: Wattson CI <wattson-external@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/20251008124510.6dba541a@gandalf.local.home
Fixes: 3d62ab32df ("tracing: Fix tracing_marker may trigger page fault during preempt_disable")
Reported-by: Runping Lai <runpinglai@google.com>
Tested-by: Runping Lai <runpinglai@google.com>
Closes: https://lore.kernel.org/linux-trace-kernel/20251007003417.3470979-2-runpinglai@google.com/
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Pull tracing updates from Steven Rostedt:
- Use READ_ONCE() and WRITE_ONCE() instead of RCU for syscall
tracepoints
Individual system call trace events are pseudo events attached to the
raw_syscall trace events that just trace the entry and exit of all
system calls. When any of these individual system call trace events
get enabled, an element in an array indexed by the system call number
is assigned to the trace file that defines how to trace it. When the
trace event triggers, it reads this array and if the array has an
element, it uses that trace file to know what to write it (the trace
file defines the output format of the corresponding system call).
The issue is that it uses rcu_dereference_ptr() and marks the
elements of the array as using RCU. This is incorrect. There is no
RCU synchronization here. The event file that is pointed to has a
completely different way to make sure its freed properly. The reading
of the array during the system call trace event is only to know if
there is a value or not. If not, it does nothing (it means this
system call isn't being traced). If it does, it uses the information
to store the system call data.
The RCU usage here can simply be replaced by READ_ONCE() and
WRITE_ONCE() macros.
- Have the system call trace events use "0x" for hex values
Some system call trace events display hex values but do not have "0x"
in front of it. Seeing "count: 44" can be assumed that it is 44
decimal when in actuality it is 44 hex (68 decimal). Display "0x44"
instead.
- Use vmalloc_array() in tracing_map_sort_entries()
The function tracing_map_sort_entries() used array_size() and
vmalloc() when it could have simply used vmalloc_array().
- Use for_each_online_cpu() in trace_osnoise.c()
Instead of open coding for_each_cpu(cpu, cpu_online_mask), use
for_each_online_cpu().
- Move the buffer field in struct trace_seq to the end
The buffer field in struct trace_seq is architecture dependent in
size, and caused padding for the fields after it. By moving the
buffer to the end of the structure, it compacts the trace_seq
structure better.
- Remove redundant zeroing of cmdline_idx field in
saved_cmdlines_buffer()
The structure that contains cmdline_idx is zeroed by memset(), no
need to explicitly zero any of its fields after that.
- Use system_percpu_wq instead of system_wq in user_event_mm_remove()
As system_wq is being deprecated, use the new wq.
- Add cond_resched() is ftrace_module_enable()
Some modules have a lot of functions (thousands of them), and the
enabling of those functions can take some time. On non preemtable
kernels, it was triggering a watchdog timeout. Add a cond_resched()
to prevent that.
- Add a BUILD_BUG_ON() to make sure PID_MAX_DEFAULT is always a power
of 2
There's code that depends on PID_MAX_DEFAULT being a power of 2 or it
will break. If in the future that changes, make sure the build fails
to ensure that the code is fixed that depends on this.
- Grab mutex_lock() before ever exiting s_start()
The s_start() function is a seq_file start routine. As s_stop() is
always called even if s_start() fails, and s_stop() expects the
event_mutex to be held as it will always release it. That mutex must
always be taken in s_start() even if that function fails.
* tag 'trace-v6.18' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Fix lock imbalance in s_start() memory allocation failure path
tracing: Ensure optimized hashing works
ftrace: Fix softlockup in ftrace_module_enable
tracing: replace use of system_wq with system_percpu_wq
tracing: Remove redundant 0 value initialization
tracing: Move buffer in trace_seq to end of struct
tracing/osnoise: Use for_each_online_cpu() instead of for_each_cpu()
tracing: Use vmalloc_array() to improve code
tracing: Have syscall trace events show "0x" for values greater than 10
tracing: Replace syscall RCU pointer assignment with READ/WRITE_ONCE()
Pull probe fix from Masami Hiramatsu:
- Fix race condition in kprobe initialization causing NULL pointer
dereference. This happens on weak memory model, which does not
correctly manage the flags access with appropriate memory barriers.
Use RELEASE-ACQUIRE to fix it.
* tag 'probes-fixes-v6.17' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Fix race condition in kprobe initialization causing NULL pointer dereference
Pull file->f_path constification from Al Viro:
"Only one thing was modifying ->f_path of an opened file - acct(2).
Massaging that away and constifying a bunch of struct path * arguments
in functions that might be given &file->f_path ends up with the
situation where we can turn ->f_path into an anon union of const
struct path f_path and struct path __f_path, the latter modified only
in a few places in fs/{file_table,open,namei}.c, all for struct file
instances that are yet to be opened"
* tag 'pull-f_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (23 commits)
Have cc(1) catch attempts to modify ->f_path
kernel/acct.c: saner struct file treatment
configfs:get_target() - release path as soon as we grab configfs_item reference
apparmor/af_unix: constify struct path * arguments
ovl_is_real_file: constify realpath argument
ovl_sync_file(): constify path argument
ovl_lower_dir(): constify path argument
ovl_get_verity_digest(): constify path argument
ovl_validate_verity(): constify {meta,data}path arguments
ovl_ensure_verity_loaded(): constify datapath argument
ksmbd_vfs_set_init_posix_acl(): constify path argument
ksmbd_vfs_inherit_posix_acl(): constify path argument
ksmbd_vfs_kern_path_unlock(): constify path argument
ksmbd_vfs_path_lookup_locked(): root_share_path can be const struct path *
check_export(): constify path argument
export_operations->open(): constify path argument
rqst_exp_get_by_name(): constify path argument
nfs: constify path argument of __vfs_getattr()
bpf...d_path(): constify path argument
done_path_create(): constify path argument
...
Pull fs_context updates from Al Viro:
"Change vfs_parse_fs_string() calling conventions
Get rid of the length argument (almost all callers pass strlen() of
the string argument there), add vfs_parse_fs_qstr() for the cases that
do want separate length"
* tag 'pull-fs_context' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
do_nfs4_mount(): switch to vfs_parse_fs_string()
change the calling conventions for vfs_parse_fs_string()
When s_start() fails to allocate memory for set_event_iter, it returns NULL
before acquiring event_mutex. However, the corresponding s_stop() function
always tries to unlock the mutex, causing a lock imbalance warning:
WARNING: bad unlock balance detected!
6.17.0-rc7-00175-g2b2e0c04f78c #7 Not tainted
-------------------------------------
syz.0.85611/376514 is trying to release lock (event_mutex) at:
[<ffffffff8dafc7a4>] traverse.part.0.constprop.0+0x2c4/0x650 fs/seq_file.c:131
but there are no more locks to release!
The issue was introduced by commit b355247df1 ("tracing: Cache ':mod:'
events for modules not loaded yet") which added the kzalloc() allocation before
the mutex lock, creating a path where s_start() could return without locking
the mutex while s_stop() would still try to unlock it.
Fix this by unconditionally acquiring the mutex immediately after allocation,
regardless of whether the allocation succeeded.
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/20250929113238.3722055-1-sashal@kernel.org
Fixes: b355247df1 ("tracing: Cache ":mod:" events for modules not loaded yet")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Pull bpf updates from Alexei Starovoitov:
- Support pulling non-linear xdp data with bpf_xdp_pull_data() kfunc
(Amery Hung)
Applied as a stable branch in bpf-next and net-next trees.
- Support reading skb metadata via bpf_dynptr (Jakub Sitnicki)
Also a stable branch in bpf-next and net-next trees.
- Enforce expected_attach_type for tailcall compatibility (Daniel
Borkmann)
- Replace path-sensitive with path-insensitive live stack analysis in
the verifier (Eduard Zingerman)
This is a significant change in the verification logic. More details,
motivation, long term plans are in the cover letter/merge commit.
- Support signed BPF programs (KP Singh)
This is another major feature that took years to materialize.
Algorithm details are in the cover letter/marge commit
- Add support for may_goto instruction to s390 JIT (Ilya Leoshkevich)
- Add support for may_goto instruction to arm64 JIT (Puranjay Mohan)
- Fix USDT SIB argument handling in libbpf (Jiawei Zhao)
- Allow uprobe-bpf program to change context registers (Jiri Olsa)
- Support signed loads from BPF arena (Kumar Kartikeya Dwivedi and
Puranjay Mohan)
- Allow access to union arguments in tracing programs (Leon Hwang)
- Optimize rcu_read_lock() + migrate_disable() combination where it's
used in BPF subsystem (Menglong Dong)
- Introduce bpf_task_work_schedule*() kfuncs to schedule deferred
execution of BPF callback in the context of a specific task using the
kernel’s task_work infrastructure (Mykyta Yatsenko)
- Enforce RCU protection for KF_RCU_PROTECTED kfuncs (Kumar Kartikeya
Dwivedi)
- Add stress test for rqspinlock in NMI (Kumar Kartikeya Dwivedi)
- Improve the precision of tnum multiplier verifier operation
(Nandakumar Edamana)
- Use tnums to improve is_branch_taken() logic (Paul Chaignon)
- Add support for atomic operations in arena in riscv JIT (Pu Lehui)
- Report arena faults to BPF error stream (Puranjay Mohan)
- Search for tracefs at /sys/kernel/tracing first in bpftool (Quentin
Monnet)
- Add bpf_strcasecmp() kfunc (Rong Tao)
- Support lookup_and_delete_elem command in BPF_MAP_STACK_TRACE (Tao
Chen)
* tag 'bpf-next-6.18' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (197 commits)
libbpf: Replace AF_ALG with open coded SHA-256
selftests/bpf: Add stress test for rqspinlock in NMI
selftests/bpf: Add test case for different expected_attach_type
bpf: Enforce expected_attach_type for tailcall compatibility
bpftool: Remove duplicate string.h header
bpf: Remove duplicate crypto/sha2.h header
libbpf: Fix error when st-prefix_ops and ops from differ btf
selftests/bpf: Test changing packet data from kfunc
selftests/bpf: Add stacktrace map lookup_and_delete_elem test case
selftests/bpf: Refactor stacktrace_map case with skeleton
bpf: Add lookup_and_delete_elem for BPF_MAP_STACK_TRACE
selftests/bpf: Fix flaky bpf_cookie selftest
selftests/bpf: Test changing packet data from global functions with a kfunc
bpf: Emit struct bpf_xdp_sock type in vmlinux BTF
selftests/bpf: Task_work selftest cleanup fixes
MAINTAINERS: Delete inactive maintainers from AF_XDP
bpf: Mark kfuncs as __noclone
selftests/bpf: Add kprobe multi write ctx attach test
selftests/bpf: Add kprobe write ctx attach test
selftests/bpf: Add uprobe context ip register change test
...
A soft lockup was observed when loading amdgpu module.
If a module has a lot of tracable functions, multiple calls
to kallsyms_lookup can spend too much time in RCU critical
section and with disabled preemption, causing kernel panic.
This is the same issue that was fixed in
commit d0b24b4e91 ("ftrace: Prevent RCU stall on PREEMPT_VOLUNTARY
kernels") and commit 42ea22e754 ("ftrace: Add cond_resched() to
ftrace_graph_set_hash()").
Fix it the same way by adding cond_resched() in ftrace_module_enable.
Link: https://lore.kernel.org/aMQD9_lxYmphT-up@vova-pc
Signed-off-by: Vladimir Riabchun <ferr.lambarginio@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Pull tracing fixes from Steven Rostedt:
- Fix buffer overflow in osnoise_cpu_write()
The allocated buffer to read user space did not add a nul terminating
byte after copying from user the string. It then reads the string,
and if user space did not add a nul byte, the read will continue
beyond the string.
Add a nul terminating byte after reading the string.
- Fix missing check for lockdown on tracing
There's a path from kprobe events or uprobe events that can update
the tracing system even if lockdown on tracing is activate. Add a
check in the dynamic event path.
- Add a recursion check for the function graph return path
Now that fprobes can hook to the function graph tracer and call
different code between the entry and the exit, the exit code may now
call functions that are not called in entry. This means that the exit
handler can possibly trigger recursion that is not caught and cause
the system to crash.
Add the same recursion checks in the function exit handler as exists
in the entry handler path.
* tag 'trace-v6.17-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: fgraph: Protect return handler from recursion loop
tracing: dynevent: Add a missing lockdown check on dynevent
tracing/osnoise: Fix slab-out-of-bounds in _parse_integer_limit()
function_graph_enter_regs() prevents itself from recursion by
ftrace_test_recursion_trylock(), but __ftrace_return_to_handler(),
which is called at the exit, does not prevent such recursion.
Therefore, while it can prevent recursive calls from
fgraph_ops::entryfunc(), it is not able to prevent recursive calls
to fgraph from fgraph_ops::retfunc(), resulting in a recursive loop.
This can lead an unexpected recursion bug reported by Menglong.
is_endbr() is called in __ftrace_return_to_handler -> fprobe_return
-> kprobe_multi_link_exit_handler -> is_endbr.
To fix this issue, acquire ftrace_test_recursion_trylock() in the
__ftrace_return_to_handler() after unwind the shadow stack to mark
this section must prevent recursive call of fgraph inside user-defined
fgraph_ops::retfunc().
This is essentially a fix to commit 4346ba1604 ("fprobe: Rewrite
fprobe on function-graph tracer"), because before that fgraph was
only used from the function graph tracer. Fprobe allowed user to run
any callbacks from fgraph after that commit.
Reported-by: Menglong Dong <menglong8.dong@gmail.com>
Closes: https://lore.kernel.org/all/20250918120939.1706585-1-dongml2@chinatelecom.cn/
Fixes: 4346ba1604 ("fprobe: Rewrite fprobe on function-graph tracer")
Cc: stable@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/175852292275.307379.9040117316112640553.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Menglong Dong <menglong8.dong@gmail.com>
Acked-by: Menglong Dong <menglong8.dong@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Pull probes fixes from Masami Hiramatsu:
- fprobe: Even if there is a memory allocation failure, try to remove
the addresses recorded until then from the filter. Previously we just
skipped it.
- tracing: dynevent: Add a missing lockdown check on dynevent. This
dynevent is the interface for all probe events. Thus if there is no
check, any probe events can be added after lock down the tracefs.
* tag 'probes-fixes-v6.17-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: dynevent: Add a missing lockdown check on dynevent
tracing: fprobe: Fix to remove recorded module addresses from filter
