[PATCH] sigaltstack bad behavior on powerpc64

[PATCH] sigaltstack bad behavior on powerpc64

[Laurent MEYER]

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Hello,

I may have found a bug in powerpc64 arch specific code.

*) When setting a sighandler using sigaction() call, if the flag
SA_ONSTACK is set and no alternate stack is provided via sigaltstack(),
the kernel still try to install the alternate stack. This behavior is
the opposite of the one which is documented in Single Unix
Specifications V3.

*) Also when setting an alternate stack using sigaltstack() with the flag SS_DISABLE, 
the kernel try to install the alternate stack on signal delivery.

These two use cases makes the process crash at signal delivery.

I wrote a small patch to add a condition in get_sigframe().

Hope that is relevant and helpfull.

Regards,
Laurent MEYER.

Signed-off-by: Laurent Meyer <meyerlau@fr.ibm.com>

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Index: linux-2.6.16-mcr/arch/powerpc/kernel/signal_64.c
===================================================================
--- linux-2.6.16-mcr.orig/arch/powerpc/kernel/signal_64.c	2006-03-27 11:09:02.000000000 +0200
+++ linux-2.6.16-mcr/arch/powerpc/kernel/signal_64.c	2006-03-27 11:14:16.986879573 +0200
@@ -213,7 +213,7 @@
         /* Default to using normal stack */
         newsp = regs->gpr[1];
 
-	if (ka->sa.sa_flags & SA_ONSTACK) {
+	if ((ka->sa.sa_flags & SA_ONSTACK) && current->sas_ss_size) {
 		if (! on_sig_stack(regs->gpr[1]))
 			newsp = (current->sas_ss_sp + current->sas_ss_size);
 	}

Re: [PATCH] sigaltstack bad behavior on powerpc64

[Andreas Schwab]

Laurent MEYER <meyerlau@fr.ibm.com> writes:

> Index: linux-2.6.16-mcr/arch/powerpc/kernel/signal_64.c
> ===================================================================
> --- linux-2.6.16-mcr.orig/arch/powerpc/kernel/signal_64.c	2006-03-27 11:09:02.000000000 +0200
> +++ linux-2.6.16-mcr/arch/powerpc/kernel/signal_64.c	2006-03-27 11:14:16.986879573 +0200
> @@ -213,7 +213,7 @@
>          /* Default to using normal stack */
>          newsp = regs->gpr[1];
>  
> -	if (ka->sa.sa_flags & SA_ONSTACK) {
> +	if ((ka->sa.sa_flags & SA_ONSTACK) && current->sas_ss_size) {
>  		if (! on_sig_stack(regs->gpr[1]))

This should use sas_ss_flags.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: [PATCH] sigaltstack bad behavior on powerpc64

[Paul Mackerras]

Laurent MEYER writes:

> I may have found a bug in powerpc64 arch specific code.

Yes, you're right, it's a bug.

> I wrote a small patch to add a condition in get_sigframe().

Looks correct.  Thanks.  I'll put it in.

Paul.