Re: [Bug #12505] 2.6.29-rc1 Firefox crashing on page load

From: Justin P. Mattock
Date: Wed Jan 21 2009 - 04:40:59 EST

Justin Madru wrote:
Ingo Molnar wrote:
* Ingo Molnar <mingo@xxxxxxx> wrote:

* Ingo Molnar <mingo@xxxxxxx> wrote:

(added Cc:s)
Justin, does it work if you apply the patch below instead of the revert?
hm, that patch wont build because the protect_asmlinkage macro is rather limited - it cannot deal with structure parameters.

We might be better off with a revert here, and a comment added that points out the problem.

Below is the revert+document commit that i have queued up.

Justin, could you try the tip/master tree (which has this fix included):

does Firefox still work fine?


>From 779c9b9f8cb87cdfbd299ee7beb62e50ce139a92 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@xxxxxxx>
Date: Tue, 20 Jan 2009 09:31:49 +0100
Subject: [PATCH] Revert "x86: signal: change type of paramter for sys_rt_sigreturn()"

This reverts commit 4217458dafaa57d8e26a46f5d05ab8c53cf64191.

Justin Madru bisected this commit, it was causing weird Firefox

The reason is that GCC mis-optimizes (re-uses) the on-stack parameters of
the calling frame, which corrupts the syscall return pt_regs state and
thus corrupts user-space register state.

So we go back to the slightly less clean but more optimization-safe
method of getting to pt_regs. Also add a comment to explain this.


Reported-and-bisected-by: Justin Madru <jdm64@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
arch/x86/include/asm/syscalls.h | 2 +-
arch/x86/kernel/signal.c | 11 +++++++++--
2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h
index 9c6797c..c0b0bda 100644
--- a/arch/x86/include/asm/syscalls.h
+++ b/arch/x86/include/asm/syscalls.h
@@ -40,7 +40,7 @@ asmlinkage int sys_sigaction(int, const struct old_sigaction __user *,
struct old_sigaction __user *);
asmlinkage int sys_sigaltstack(unsigned long);
asmlinkage unsigned long sys_sigreturn(unsigned long);
-asmlinkage int sys_rt_sigreturn(struct pt_regs);
+asmlinkage int sys_rt_sigreturn(unsigned long);
/* kernel/ioport.c */
asmlinkage long sys_iopl(unsigned long);
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 89bb766..df0587f 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -632,9 +632,16 @@ badframe:
#ifdef CONFIG_X86_32
-asmlinkage int sys_rt_sigreturn(struct pt_regs regs)
+ * Note: do not pass in pt_regs directly as with tail-call optimization
+ * GCC will incorrectly stomp on the caller's frame and corrupt user-space
+ * register state:
+ */
+asmlinkage int sys_rt_sigreturn(unsigned long __unused)
- return do_rt_sigreturn(&regs);
+ struct pt_regs *regs = (struct pt_regs *)&__unused;
+ return do_rt_sigreturn(regs);
#else /* !CONFIG_X86_32 */
asmlinkage long sys_rt_sigreturn(struct pt_regs *regs)

Ok, I officially tested tip/master and firefox is happy it can talk to friends with google talk ;-)
Although.... I don't use google talk.... it just seems to be this mandatory tab I can't get rid of
on my google page that caused a regression to be noticed so that the kernel could be improved!

Justin Madru

Well I guess the problem has been bisected.


Justin P. Mattock
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