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

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Message-ID: <4976ED99.3070007@gmail.com>
Date:	Wed, 21 Jan 2009 01:40:41 -0800
From:	"Justin P. Mattock" <justinmattock@...il.com>
To:	Justin Madru <jdm64@...ab.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Roland McGrath <roland@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [Bug #12505] 2.6.29-rc1 Firefox crashing on page load

Justin Madru wrote:
> Ingo Molnar wrote:
>> * Ingo Molnar <mingo@...e.hu> wrote:
>>
>>  
>>> * Ingo Molnar <mingo@...e.hu> 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):
>>
>>   http://people.redhat.com/mingo/tip.git/README
>>
>> does Firefox still work fine?
>>
>>     Ingo
>>
>> ------------->
>> >From 779c9b9f8cb87cdfbd299ee7beb62e50ce139a92 Mon Sep 17 00:00:00 2001
>> From: Ingo Molnar <mingo@...e.hu>
>> 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
>> crashes.
>>
>> 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.
>>
>> Resolves: http://bugzilla.kernel.org/show_bug.cgi?id=12505
>>
>> Reported-and-bisected-by: Justin Madru <jdm64@...ab.com>
>> Signed-off-by: Ingo Molnar <mingo@...e.hu>
>> ---
>>  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.

regards;

Justin P. Mattock
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