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    SubjectRe: vm86.c audit_syscall_exit() call trashes registers
    William Cattey wrote:
    > Your fix seems to have remedied a problem we are having with EDID
    > fetches through vm86.c. At the present moment, we're trying to
    > understand your cleanup so as to back port it to an earlier rev of the
    > kernel (2.6.18).
    > 3 questions for you:
    > 1. Are we correct in understanding that your cleanup only touched
    > vm86.c and vm86.h?
    > 2. Do you remember your changes well enough from back when you made
    > them in December 2006 to be able to point out the changes solely made
    > to the audit calls?
    > 3. Does correct operation of vm86.c in the 2.6 kernel require all of
    > your changes, or just the subset that affects the audit calls?

    It was only a small part of the patch. I think it was basically this
    hunk (hand-edited, so this won't apply directly):

    @@ -306,19 +334,18 @@ static void do_sys_vm86(struct kernel_vm
    tsk->thread.screen_bitmap = info->screen_bitmap;
    if (info->flags & VM86_SCREEN_BITMAP)
    __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);

    This is certainly a bogus piece of code, and it could result in more or
    less random values of eax being passed to audit_syscall_exit(). But I
    don't know if it will have any bearing on your EDID problem; the rest of
    the patch is related to the introduction of using %gs as the base for
    the per-processor data area, and shouldn't cause any functional change
    to sys_vm86(), but its possible I fixed some other bug in the process.

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      Last update: 2007-09-29 08:09    [W:0.021 / U:11.652 seconds]
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