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Subject[PATCH 5.0 156/238] powerpc/32: Clear on-stack exception marker upon exception return
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5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christophe Leroy <christophe.leroy@c-s.fr>

commit 9580b71b5a7863c24a9bd18bcd2ad759b86b1eff upstream.

Clear the on-stack STACK_FRAME_REGS_MARKER on exception exit in order
to avoid confusing stacktrace like the one below.

Call Trace:
[c0e9dca0] [c01c42a0] print_address_description+0x64/0x2bc (unreliable)
[c0e9dcd0] [c01c4684] kasan_report+0xfc/0x180
[c0e9dd10] [c0895130] memchr+0x24/0x74
[c0e9dd30] [c00a9e38] msg_print_text+0x124/0x574
[c0e9dde0] [c00ab710] console_unlock+0x114/0x4f8
[c0e9de40] [c00adc60] vprintk_emit+0x188/0x1c4
--- interrupt: c0e9df00 at 0x400f330
LR = init_stack+0x1f00/0x2000
[c0e9de80] [c00ae3c4] printk+0xa8/0xcc (unreliable)
[c0e9df20] [c0c27e44] early_irq_init+0x38/0x108
[c0e9df50] [c0c15434] start_kernel+0x310/0x488
[c0e9dff0] [00003484] 0x3484

With this patch the trace becomes:

Call Trace:
[c0e9dca0] [c01c42c0] print_address_description+0x64/0x2bc (unreliable)
[c0e9dcd0] [c01c46a4] kasan_report+0xfc/0x180
[c0e9dd10] [c0895150] memchr+0x24/0x74
[c0e9dd30] [c00a9e58] msg_print_text+0x124/0x574
[c0e9dde0] [c00ab730] console_unlock+0x114/0x4f8
[c0e9de40] [c00adc80] vprintk_emit+0x188/0x1c4
[c0e9de80] [c00ae3e4] printk+0xa8/0xcc
[c0e9df20] [c0c27e44] early_irq_init+0x38/0x108
[c0e9df50] [c0c15434] start_kernel+0x310/0x488
[c0e9dff0] [00003484] 0x3484

Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/kernel/entry_32.S | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -745,6 +745,9 @@ fast_exception_return:
mtcr r10
lwz r10,_LINK(r11)
mtlr r10
+ /* Clear the exception_marker on the stack to avoid confusing stacktrace */
+ li r10, 0
+ stw r10, 8(r11)
REST_GPR(10, r11)
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
mtspr SPRN_NRI, r0
@@ -982,6 +985,9 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRE
mtcrf 0xFF,r10
mtlr r11

+ /* Clear the exception_marker on the stack to avoid confusing stacktrace */
+ li r10, 0
+ stw r10, 8(r1)
/*
* Once we put values in SRR0 and SRR1, we are in a state
* where exceptions are not recoverable, since taking an
@@ -1021,6 +1027,9 @@ exc_exit_restart_end:
mtlr r11
lwz r10,_CCR(r1)
mtcrf 0xff,r10
+ /* Clear the exception_marker on the stack to avoid confusing stacktrace */
+ li r10, 0
+ stw r10, 8(r1)
REST_2GPRS(9, r1)
.globl exc_exit_restart
exc_exit_restart:

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