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Commit 3aa6b186 authored by Lubomir Rintel's avatar Lubomir Rintel Committed by Ingo Molnar
Browse files

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



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: default avatarLubomir Rintel <lkundrak@v3.sk>
Cc: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <1244384628.2323.4.camel@bimbo>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 4a4aca64

arch/x86/kernel/vm86_32.c

+5 −4
Original line number Diff line number Diff line
@@ -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));