linux-kernel - Re: linux-next: WARNING: at kernel/panic.c:375 __stack_chk

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Date:	Thu, 01 May 2008 19:37:42 -0300
From:	Kevin Winchester <kjwinchester@...il.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: linux-next: WARNING: at kernel/panic.c:375 __stack_chk_test+0x50/0x54()

Arjan van de Ven wrote:
> On Wed, 30 Apr 2008 21:24:27 -0300
> Kevin Winchester <kjwinchester@...il.com> wrote:
> 
>> Arjan van de Ven wrote:
>>> Kevin Winchester wrote:
>>>> Hi Arjan,
>>>>
>>>> There doesn't seem to be an entry in MAINTAINERS for stack
>>>> protector, but your signoff was on the last stack protector
>>>> related commit I could find, so it's probably a good bet.
>>>>
>>>> I get the following in my dmesg after testing linux-next with the
>>>> stack protector turned on.  This is an x86-64 UP box if that
>>>> helps.  It appears to be related to the test for the feature (or
>>>> perhaps that is supposed to happen when the feature is tested, I'm
>>>> not sure...).  Config below.
>>>>
>>> the important question is: exactly what gcc are you using? (and if
>>> you use a distro gcc, which distro)
>>>
>>> second question would be, what does the following command give?
>>>
>>> echo "int foo(void) { char X[200]; return 3; }" | $1 -S -xc -c -O0
>>> -mcmodel=kernel -fstack-protector - -o -
>>>
>>> (this is the command from scripts/gcc-x86_64-has-stack-protector.sh
>>> that the kernel uses to test at compiletime if you have stack
>>> protector support)
>> Ubuntu Hardy Heron
>>
>> kevin@...khine:~$ gcc --version
>> gcc (GCC) 4.2.3 (Ubuntu 4.2.3-2ubuntu7)
>> Copyright (C) 2007 Free Software Foundation, Inc.
>> This is free software; see the source for copying conditions.  There
>> is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
>> PARTICULAR PURPOSE.
>>
>>
>> kevin@...khine:~$ echo "int foo(void) { char X[200]; return 3; }" |
>> $1 -S -xc -c -O0 -mcmodel=kernel -fstack-protector - -o - bash: -S:
>> command not found
>>
>> I assume that $1 was supposed to be gcc, so how about:
> 
> eh woops yes
> 
>> kevin@...khine:~/linux/linux-2.6/scripts$ sh
>> gcc-x86_64-has-stack-protector.sh gcc something something
>>
>> So I would assume that means I pass...
> 
> 
> I would rather really like to see the assembly output this thing spits; to see if your compiler behaves sanely.
> (Some distros tend to badly patch their gcc unfortunately and this may break the stack protector feature)

Sure, here we go:

kevin@...khine:~$ echo "int foo(void) { char X[200]; return 3; }" | gcc -S -xc -c -O0 -mcmodel=kernel -fstack-protector - -o -
        .file   ""
        .text
.globl foo
        .type   foo, @function
foo:
.LFB2:
        pushq   %rbp
.LCFI0:
        movq    %rsp, %rbp
.LCFI1:
        subq    $208, %rsp
.LCFI2:
        movq    %gs:40, %rax
        movq    %rax, -8(%rbp)
        xorl    %eax, %eax
        movl    $3, %eax
        movq    -8(%rbp), %rdx
        xorq    %gs:40, %rdx
        je      .L3
        call    __stack_chk_fail
.L3:
        leave
        ret
.LFE2:
        .size   foo, .-foo
        .section        .eh_frame,"a",@progbits
.Lframe1:
        .long   .LECIE1-.LSCIE1
.LSCIE1:
        .long   0x0
        .byte   0x1
        .string ""
        .uleb128 0x1
        .sleb128 -8
        .byte   0x10
        .byte   0xc
        .uleb128 0x7
        .uleb128 0x8
        .byte   0x90
        .uleb128 0x1
        .align 8
.LECIE1:
.LSFDE1:
        .long   .LEFDE1-.LASFDE1
.LASFDE1:
        .long   .LASFDE1-.Lframe1
        .quad   .LFB2
        .quad   .LFE2-.LFB2
        .byte   0x4
        .long   .LCFI0-.LFB2
        .byte   0xe
        .uleb128 0x10
        .byte   0x86
        .uleb128 0x2
        .byte   0x4
        .long   .LCFI1-.LCFI0
        .byte   0xd
        .uleb128 0x6
        .align 8
.LEFDE1:
        .ident  "GCC: (GNU) 4.2.3 (Ubuntu 4.2.3-2ubuntu7)"
        .section        .note.GNU-stack,"",@progbits

Does that help?

-- 
Kevin Winchester
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