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

commit 9e1ba4f27f018742a1aa95d11e35106feba08ec1 upstream.

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()")
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
[mpe: Change log massage, add stable tag]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 6432d4bf08c8..767ef6d68c9e 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -689,7 +689,7 @@ resume_kernel:
 
         addi    r8,r1,INT_FRAME_SIZE    /* Get the kprobed function entry */
 
-        lwz     r3,GPR1(r1)
+        ld      r3,GPR1(r1)
         subi    r3,r3,INT_FRAME_SIZE    /* dst: Allocate a trampoline exception frame */
         mr      r4,r1                   /* src:  current exception frame */
         mr      r1,r3                   /* Reroute the trampoline frame to r1 */
@@ -703,8 +703,8 @@ resume_kernel:
         addi    r6,r6,8
         bdnz    2b
 
-        /* Do real store operation to complete stwu */
-        lwz     r5,GPR1(r1)
+        /* Do real store operation to complete stdu */
+        ld      r5,GPR1(r1)
         std     r8,0(r5)
 
         /* Clear _TIF_EMULATE_STACK_STORE flag */