powerpc/optprobes: Fix TOC handling in optprobes trampoline
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: 762df10bad69 ("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>
1 file changed