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SubjectRe: vm86.c audit_syscall_exit() call trashes registers
Date
Thanks very much for thinking about this and providing a revised  
candidate patch.

Sadly, the effect of the patch is the same as the most recent
candidate patch from Jeremy Fitzhardinge: The EDID transfer still
comes up all zeros.

This is very perplexing to me. If I take the code that appears in
2.6.18's vm86.c, and simply put #if 0 around the call to
audit_syscall_exit I get good data.

If this is indeed a correct minimal correction to the
audit_syscall_exit code, then perhaps there's some other condition
being exercised. I guess my next step is to take the whole pt_regs
patch (commit 49d26b6eaa8e970c8cf6e299e6ccba2474191bf5) from
kernel.org and see if that has a beneficial effect.

-Bill

----

William Cattey
Linux Platform Coordinator
MIT Information Services & Technology

N42-040M, 617-253-0140, wdc@mit.edu
http://web.mit.edu/wdc/www/


On Oct 2, 2007, at 12:44 PM, Chuck Ebbert wrote:

> On 09/25/2007 07:38 PM, William Cattey wrote:
>>
>> I'd feel a lot more confident we were on the right track if I
>> could just
>> correctly patch Fitzhardinge's cleanup into the test setup I have
>> now.
>>
>
> I think you need to zero both registers if you're using 2.6.16, and
> force
> %eax as the source so it doesn't choose %ebp?
>
> --- a/arch/i386/kernel/vm86.c
> +++ b/arch/i386/kernel/vm86.c
> @@ -306,19 +334,19 @@ static void do_sys_vm86(struct
> kernel_vm86_struct *info, struct task_struct *tsk
> tsk->thread.screen_bitmap = info->screen_bitmap;
> if (info->flags & VM86_SCREEN_BITMAP)
> mark_screen_rdonly(tsk->mm);
> - __asm__ __volatile__("xorl %eax,%eax; movl %eax,%fs; movl %eax,%gs
> \n\t");
> - __asm__ __volatile__("movl %%eax, %0\n" :"=r"(eax));
>
> /*call audit_syscall_exit since we do not exit via the normal
> paths */
> if (unlikely(current->audit_context))
> - audit_syscall_exit(AUDITSC_RESULT(eax), eax);
> + audit_syscall_exit(AUDITSC_RESULT(0), 0);
>
> __asm__ __volatile__(
> "movl %0,%%esp\n\t"
> "movl %1,%%ebp\n\t"
> + "mov %2, %%fs\n\t"
> + "mov %2, %%gs\n\t"
> "jmp resume_userspace"
> : /* no outputs */
> - :"r" (&info->regs), "r" (task_thread_info(tsk)));
> + :"r" (&info->regs), "r" (task_thread_info(tsk)), "a" (0));
> /* we never return here */
> }
>

-
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