2008-02-18 10:26:53

by Shi Weihua

Subject: [PATCH 2/5] signal(x86_64): add a signal stack overflow check

The similar check has been added to x86_32(i386) in commit
id 83bd01024b1fdfc41d9b758e5669e80fca72df66.
So we add this check to x86_64 and improve it a liitle bit in that
we need to check for stack overflow only when the signal is on stack.

Signed-off-by: Shi Weihua <[email protected]>

---
--- linux-2.6.25-rc2.orig/arch/x86/kernel/signal_64.c 2008-02-16 04:57:20.000000000 +0800
+++ linux-2.6.25-rc2/arch/x86/kernel/signal_64.c 2008-02-18 18:06:48.000000000 +0800
@@ -205,8 +205,19 @@ get_stack(struct k_sigaction *ka, struct

/* This is the X/Open sanctioned signal stack switching. */
if (ka->sa.sa_flags & SA_ONSTACK) {
- if (sas_ss_flags(sp) == 0)
+ int onstack = sas_ss_flags(sp);
+
+ if (onstack == 0)
sp = current->sas_ss_sp + current->sas_ss_size;
+ else if (onstack == SS_ONSTACK) {
+ /*
+ * If we are on the alternate signal stack and would
+ * overflow it, don't return an always-bogus address
+ * instead so we will die with SIGSEGV.
+ */
+ if (!likely(on_sig_stack(sp - size)))
+ return (void __user *) -1L;
+ }
}

return (void __user *)round_down(sp - size, 16);

2008-02-19 02:24:10

by Shi Weihua

Subject: Re: [PATCH 2/5] signal(x86_64): add a signal stack overflow check

The similar check has been added to x86_32(i386) in commit
id 83bd01024b1fdfc41d9b758e5669e80fca72df66.
So we add this check to x86_64 and improve it a liitle bit in that
we need to check for stack overflow only when the signal is on stack.

Signed-off-by: Shi Weihua <[email protected]>

---

The previous patch has a comment mistake. Now I correct it.

---
--- linux-2.6.25-rc2.orig/arch/x86/kernel/signal_64.c 2008-02-16 04:57:20.000000000 +0800
+++ linux-2.6.25-rc2/arch/x86/kernel/signal_64.c 2008-02-19 09:56:20.000000000 +0800
@@ -205,8 +205,19 @@ get_stack(struct k_sigaction *ka, struct

/* This is the X/Open sanctioned signal stack switching. */
if (ka->sa.sa_flags & SA_ONSTACK) {
- if (sas_ss_flags(sp) == 0)
+ int onstack = sas_ss_flags(sp);
+
+ if (onstack == 0)
sp = current->sas_ss_sp + current->sas_ss_size;
+ else if (onstack == SS_ONSTACK) {
+ /*
+ * If we are on the alternate signal stack and would
+ * overflow it, don't. Return an always-bogus address
+ * instead so we will die with SIGSEGV.
+ */
+ if (!likely(on_sig_stack(sp - size)))
+ return (void __user *) -1L;
+ }
}

return (void __user *)round_down(sp - size, 16);

2008-02-19 11:11:35

by Ingo Molnar

Subject: Re: [PATCH 2/5] signal(x86_64): add a signal stack overflow check

* Shi Weihua <[email protected]> wrote:

> The similar check has been added to x86_32(i386) in commit id
> 83bd01024b1fdfc41d9b758e5669e80fca72df66. So we add this check to
> x86_64 and improve it a liitle bit in that we need to check for stack
> overflow only when the signal is on stack.

thanks, applied.

Ingo