4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxxxxxxxxxx>
[mpe: Change log massage, add stable tag]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/kernel/entry_64.S | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -716,7 +716,7 @@ 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 */
@@ -730,8 +730,8 @@ 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 */