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f558b37bf4
Optprobes on powerpc are limited to kernel text area. We decided to also
optimize kretprobe_trampoline since that is also in kernel text area.
However,we failed to take into consideration the fact that the same
trampoline is also used to catch function returns from kernel modules.
As an example:
$ sudo modprobe kobject-example
$ sudo bash -c "echo 'r foo_show+8' > /sys/kernel/debug/tracing/kprobe_events"
$ sudo bash -c "echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable"
$ sudo cat /sys/kernel/debug/kprobes/list
c000000000041350 k kretprobe_trampoline+0x0 [OPTIMIZED]
d000000000e00200 r foo_show+0x8 kobject_example
$ cat /sys/kernel/kobject_example/foo
Segmentation fault
With the below (trimmed) splat in dmesg:
Unable to handle kernel paging request for data at address 0xfec40000
Faulting instruction address: 0xc000000000041540
Oops: Kernel access of bad area, sig: 11 [#1]
...
NIP [c000000000041540] optimized_callback+0x70/0xe0
LR [c000000000041e60] optinsn_slot+0xf8/0x10000
Call Trace:
[c0000000c7327850] [c000000000289af4] alloc_set_pte+0x1c4/0x860 (unreliable)
[c0000000c7327890] [c000000000041e60] optinsn_slot+0xf8/0x10000
--- interrupt: 700 at 0xc0000000c7327a80
LR = kretprobe_trampoline+0x0/0x10
[c0000000c7327ba0] [c0000000003a30d4] sysfs_kf_seq_show+0x104/0x1d0
[c0000000c7327bf0] [c0000000003a0bb4] kernfs_seq_show+0x44/0x60
[c0000000c7327c10] [c000000000330578] seq_read+0xf8/0x560
[c0000000c7327cb0] [c0000000003a1e64] kernfs_fop_read+0x194/0x260
[c0000000c7327d00] [c0000000002f9954] __vfs_read+0x44/0x1a0
[c0000000c7327d90] [c0000000002fb4cc] vfs_read+0xbc/0x1b0
[c0000000c7327de0] [c0000000002fd138] SyS_read+0x68/0x110
[c0000000c7327e30] [c00000000000b8e0] system_call+0x38/0xfc
Fix this by loading up the kernel TOC before calling into the kernel.
The original TOC gets restored as part of the usual pt_regs restore.
Fixes: 762df10bad ("powerpc/kprobes: Optimize kprobe in kretprobe_trampoline()")
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.