Re: [BUG] broken ebba638ae723d8a8fc2f7abce5ec18b688b791d7

[matthieu castet]

Kees Cook a écrit :
> Hi,
>
> On Thu, Jan 27, 2011 at 06:24:14PM -0800, H. Peter Anvin wrote:
> > On 01/27/2011 03:00 PM, Kees Cook wrote:
> > > Yikes, good catch.
> > >
> > > arch/x86/kernel/trampoline_64.S uses:
> > >         movw    $(trampoline_stack_end - r_base), %sp
> > >
> > > arch/x86/boot/compressed/head_64.S uses:
> > >         movl    $boot_stack_end, %eax
> > >         addl    %ebp, %eax
> > >         movl    %eax, %esp
> > >
> > > what would be safe for arch/x86/kernel/head_32.S ? It uses "stack_start",
> > > but later after paging set-up. Is the following sane to solve this?
> > To run it before paging is set up, you can't use stack, start; you
> > have to use a pointer based on physical address.  You have two
> > problems with using stack_start: you're using a linear address to
> > access stack_start, and stack_start itself contains a linear
> > address.
> >
> > It's not entirely clear to me why we don't initialize %ss to
> > __BOOT_DS with the other segment registers, but it would make most
> > sense to me:
> >
> > diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
> > index fc293dc..c10f9ba 100644
> > --- a/arch/x86/kernel/head_32.S
> > +++ b/arch/x86/kernel/head_32.S
> > @@ -99,7 +99,12 @@ ENTRY(startup_32)
> >         movl %eax,%es
> >         movl %eax,%fs
> >         movl %eax,%gs
> > +       movl %eax,%ss
> >  2:
> > +/*
> > + * Set up an initial stack
> > + */
> > +       movl $pa(init_thread_union+THREAD_SIZE), %esp
> >
> >  /*
> >   * Clear BSS first so that there are no surprises...
>
> This doesn't appear to work for me. While I can boot fine, doing CPU
> hotplugging hangs the system. :(
That's because of NX :)

The stack is marked NX, 
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