* [PATCH] arm: Fix an incorrect check in ____longjmp_chk [BZ #27709]
@ 2021-04-08 17:47 Szabolcs Nagy
2021-04-12 12:45 ` Andreas Schwab
0 siblings, 1 reply; 2+ messages in thread
From: Szabolcs Nagy @ 2021-04-08 17:47 UTC (permalink / raw)
To: libc-alpha
An incorrect check in __longjmp_chk could fail on valid code causing
FAIL: debug/tst-longjmp_chk2
The original check was
altstack_sp + altstack_size - setjmp_sp > altstack_size
i.e. sp at setjmp was outside of the altstack range. Here we know that
longjmp is called from a signal handler on the altstack (SS_ONSTACK),
and that it jumps in the wrong direction (sp decreases), so the check
wants to ensure the jump goes to another stack.
The check is wrong when altstack_sp == setjmp_sp which can happen
when the altstack is a local buffer in the function that calls setjmp,
so the patch allows == too. This fixes bug 27709.
Note that the generic __longjmp_chk check seems to be different.
(it checks if longjmp was on the altstack but does not check setjmp,
so it would not catch incorrect longjmp use within the signal handler).
---
sysdeps/unix/sysv/linux/arm/____longjmp_chk.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/arm/____longjmp_chk.S b/sysdeps/unix/sysv/linux/arm/____longjmp_chk.S
index 7f35b4da7e..a26315b7cf 100644
--- a/sysdeps/unix/sysv/linux/arm/____longjmp_chk.S
+++ b/sysdeps/unix/sysv/linux/arm/____longjmp_chk.S
@@ -72,8 +72,8 @@ longjmp_msg:
ldr r3, [sp, #8]; \
add r2, r2, r3; \
sub r2, r2, reg; \
- cmp r2, r3; \
- bhi .Lok2; \
+ cmp r3, r2; \
+ bls .Lok2; \
.Lfail: \
add sp, sp, #12; \
cfi_adjust_cfa_offset (-12); \
--
2.17.1
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] arm: Fix an incorrect check in ____longjmp_chk [BZ #27709]
2021-04-08 17:47 [PATCH] arm: Fix an incorrect check in ____longjmp_chk [BZ #27709] Szabolcs Nagy
@ 2021-04-12 12:45 ` Andreas Schwab
0 siblings, 0 replies; 2+ messages in thread
From: Andreas Schwab @ 2021-04-12 12:45 UTC (permalink / raw)
To: Szabolcs Nagy via Libc-alpha; +Cc: Szabolcs Nagy
On Apr 08 2021, Szabolcs Nagy via Libc-alpha wrote:
> An incorrect check in __longjmp_chk could fail on valid code causing
>
> FAIL: debug/tst-longjmp_chk2
>
> The original check was
>
> altstack_sp + altstack_size - setjmp_sp > altstack_size
>
> i.e. sp at setjmp was outside of the altstack range. Here we know that
> longjmp is called from a signal handler on the altstack (SS_ONSTACK),
> and that it jumps in the wrong direction (sp decreases), so the check
> wants to ensure the jump goes to another stack.
>
> The check is wrong when altstack_sp == setjmp_sp which can happen
> when the altstack is a local buffer in the function that calls setjmp,
> so the patch allows == too. This fixes bug 27709.
>
> Note that the generic __longjmp_chk check seems to be different.
> (it checks if longjmp was on the altstack but does not check setjmp,
> so it would not catch incorrect longjmp use within the signal handler).
Ok.
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
"And now for something completely different."
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2021-04-08 17:47 [PATCH] arm: Fix an incorrect check in ____longjmp_chk [BZ #27709] Szabolcs Nagy
2021-04-12 12:45 ` Andreas Schwab
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