Re: linux-next: WARNING: at kernel/panic.c:375 __stack_chk_test+0x50/0x54()

[Kevin Winchester]

Arjan van de Ven wrote:
> On Wed, 30 Apr 2008 21:24:27 -0300
> Kevin Winchester <kjwinchester@xxxxxxxxx> 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; }" | $1 -S -xc -c -O0
> > > -mcmodel=kernel -fstack-protector - -o -
> > >
> > > (this is the command from scripts/gcc-x86_64-has-stack-protector.sh
> > > that the kernel uses to test at compiletime if you have stack
> > > protector support)
> > Ubuntu Hardy Heron
> >
> > kevin@alekhine:~$ 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@alekhine:~$ 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 $1 was supposed to be gcc, so how about:
>
> eh woops yes
>
> > kevin@alekhine:~/linux/linux-2.6/scripts$ 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@alekhine:~$ 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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