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Subject[PATCH] ARM: fix race in for_each_frame
Date
The sv_pc, which is saved in the stack, may be an invalid address
if the target thread is running on another processor in the meantime.
It will cause kernel crash at `ldr r2, [sv_pc, #-4]`.

Check if sv_pc is valid before use it like unwind_frame in
arch/arm/kernel/unwind.c.

Signed-off-by: Mike-SL Lin <mike-sl.lin@mediatek.com>
Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
---
arch/arm/lib/backtrace.S | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/arm/lib/backtrace.S b/arch/arm/lib/backtrace.S
index 582925238d65..84f06381bbfb 100644
--- a/arch/arm/lib/backtrace.S
+++ b/arch/arm/lib/backtrace.S
@@ -64,6 +64,11 @@ for_each_frame: tst frame, mask @ Check for address exceptions
sub sv_pc, sv_pc, offset @ Correct PC for prefetching
bic sv_pc, sv_pc, mask @ mask PC/LR for the mode

+ mov r0, sv_pc
+ bl kernel_text_address @ check if sv_pc is valid
+ cmp r0, #0 @ if sv_pc is not kernel text
+ beq 1006f @ address, abort backtrace
+
1003: ldr r2, [sv_pc, #-4] @ if stmfd sp!, {args} exists,
ldr r3, .Ldsi+4 @ adjust saved 'pc' back one
teq r3, r2, lsr #11 @ instruction
--
2.18.0
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