When using CONFIG_KMALLOC_PARTITION_RANDOM, _RET_IP_ was previously used
to identify the allocation site. _RET_IP_, however, evaluates to the
caller's parent's instruction pointer rather than the actual allocation
site; this would lead to collisions where a function performs multiple
allocations.
With the generalization to kmalloc_token_t, we now generate the token at
the outermost macro, and using _THIS_IP_ would fix this for all cases.
Unfortunately, the generic implementation of _THIS_IP_ relies on taking
the address of a local label, which is considered broken by both GCC [1]
and Clang [2] because label addresses are only expected to be used with
computed gotos. While the generic version more or less works today, it
is known to be brittle. For example, Clang -O2 always returns 1 when
this function is inlined:
static inline unsigned long get_ip(void)
{ return ({ __label__ __here; __here: (unsigned long)&&__here; }); }
To provide a reliable unique identifier without breaking architectures
relying on the generic _THIS_IP_, introduce _CODE_LOCATION_: it resolves
to _THIS_IP_ where architectures provide a safe implementation, and
falls back to a zero-cost static marker where _THIS_IP_ is broken.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071 [1]
Link: https://github.com/llvm/llvm-project/issues/138272 [2]
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Link: https://patch.msgid.link/20260511200136.3201646-2-elver@google.com
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
It was reported that under certain circumstances GCC emits ENDBR
instructions for _THIS_IP_ usage. Specifically, when it appears at the
start of a basic block -- but not elsewhere.
Since _THIS_IP_ is never used for control flow, these ENDBR
instructions are completely superfluous. Override the _THIS_IP_
definition for x86_64 to avoid this.
Less ENDBR instructions is better.
Fixes: 156ff4a544 ("x86/ibt: Base IBT bits")
Reported-by: David Kaplan <David.Kaplan@amd.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230802110323.016197440@infradead.org
