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x86: Fix non-lazy GS handling in sys_vm86()

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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>
Cc: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <1244384628.2323.4.camel@bimbo>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Lubomir Rintel 2009-06-07 16:23:48 +02:00 committed by Ingo Molnar
parent 4a4aca641b
commit 3aa6b186f8
1 changed files with 5 additions and 4 deletions
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9
arch/x86/kernel/vm86_32.c
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@ -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
@ -343,7 +342,9 @@ 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"
#ifdef CONFIG_X86_32_LAZY_GS
"mov %2, %%gs\n\t"
#endif
"jmp resume_userspace"
: /* no outputs */
:"r" (&info->regs), "r" (task_thread_info(tsk)), "r" (0));