On Tue, 2017-02-21 at 15:00:47 UTC, "Naveen N. Rao" wrote: > Optprobes on powerpc is 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: > > [70646.248029] Unable to handle kernel paging request for data at address > 0xfec40000 > [70646.248730] Faulting instruction address: 0xc000000000041540 > [70646.249210] Oops: Kernel access of bad area, sig: 11 [#1] > [snip] > [70646.259635] NIP [c000000000041540] optimized_callback+0x70/0xe0 > [70646.259962] LR [c000000000041e60] optinsn_slot+0xf8/0x10000 > [70646.260268] Call Trace: > [70646.260583] [c0000000c7327850] [c000000000289af4] > alloc_set_pte+0x1c4/0x860 (unreliable) > [70646.260910] [c0000000c7327890] [c000000000041e60] > optinsn_slot+0xf8/0x10000 > [70646.261223] --- interrupt: 700 at 0xc0000000c7327a80 > LR = kretprobe_trampoline+0x0/0x10 > [70646.261849] [c0000000c7327ba0] [c0000000003a30d4] > sysfs_kf_seq_show+0x104/0x1d0 > [70646.262135] [c0000000c7327bf0] [c0000000003a0bb4] > kernfs_seq_show+0x44/0x60 > [70646.264211] [c0000000c7327c10] [c000000000330578] seq_read+0xf8/0x560 > [70646.265142] [c0000000c7327cb0] [c0000000003a1e64] > kernfs_fop_read+0x194/0x260 > [70646.266070] [c0000000c7327d00] [c0000000002f9954] __vfs_read+0x44/0x1a0 > [70646.266977] [c0000000c7327d90] [c0000000002fb4cc] vfs_read+0xbc/0x1b0 > [70646.267860] [c0000000c7327de0] [c0000000002fd138] SyS_read+0x68/0x110 > [70646.268701] [c0000000c7327e30] [c00000000000b8e0] system_call+0x38/0xfc > [snip] > > 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. > > Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/f558b37bf4c35a54e1949f6533f39c cheers
