powerpc/kprobe: Fix oops when kprobed on 'stdu' instruction

If we set a kprobe on a 'stdu' instruction on powerpc64, we see a kernel
OOPS:

  Bad kernel stack pointer cd93c840 at c000000000009868
  Oops: Bad kernel stack pointer, sig: 6 [#1]
  ...
  GPR00: c000001fcd93cb30 00000000cd93c840 c0000000015c5e00 00000000cd93c840
  ...
  NIP [c000000000009868] resume_kernel+0x2c/0x58
  LR [c000000000006208] program_check_common+0x108/0x180

On a 64-bit system when the user probes on a 'stdu' instruction, the kernel does
not emulate actual store in emulate_step() because it may corrupt the exception
frame. So the kernel does the actual store operation in exception return code
i.e. resume_kernel().

resume_kernel() loads the saved stack pointer from memory using lwz, which only
loads the low 32-bits of the address, causing the kernel crash.

Fix this by loading the 64-bit value instead.

Fixes: be96f63375a1 ("powerpc: Split out instruction analysis part of emulate_step()")
Cc: [email protected] # v3.18+
Signed-off-by: Ravi Bangoria <[email protected]>
Reviewed-by: Naveen N. Rao <[email protected]>
Reviewed-by: Ananth N Mavinakayanahalli <[email protected]>
[mpe: Change log massage, add stable tag]
Signed-off-by: Michael Ellerman <[email protected]>

0 files changed, 0 insertions, 0 deletions