Messages in this thread |  | | Date | Sun, 7 Jun 2009 09:56:13 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] Fix non-lazy GS handling in sys_vm86() |
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* Lubomir Rintel <lkundrak@v3.sk> wrote:
> This fixes a stack corruption panic or null dereference oops due to > a bad GS in resume_userspace() when returning from sys_vm86() and calling > lockdep_sys_exit(). > > Only a problem when CONFIG_LOCKDEP and CONFIG_CC_STACKPROTECTOR enabled. > > Signed-off-by: Lubomir Rintel <lkundrak@v3.sk> > --- > arch/x86/kernel/vm86_32.c | 13 +++++++------ > 1 files changed, 7 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c > index d7ac84e..177d976 100644 > --- a/arch/x86/kernel/vm86_32.c > +++ b/arch/x86/kernel/vm86_32.c > @@ -287,10 +287,9 @@ static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk > info->regs.pt.ds = 0; > info->regs.pt.es = 0; > info->regs.pt.fs = 0; > - > -/* we are clearing gs later just before "jmp resume_userspace", > - * because it is not saved/restored. > - */ > +#ifndef CONFIG_X86_32_LAZY_GS > + info->regs.pt.gs = 0; > +#endif > > /* > * The flags register is also special: we cannot trust that the user > @@ -343,10 +342,12 @@ static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk > __asm__ __volatile__( > "movl %0,%%esp\n\t" > "movl %1,%%ebp\n\t" > - "mov %2, %%gs\n\t" > +#ifdef CONFIG_X86_32_LAZY_GS > + "mov $0, %%gs\n\t" > +#endif
That bit looks rather untested - i dont think there's an immediate constant instruction variant for segment register moves ...
Ingo
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