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Subject[PATCH] 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>
---
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
"jmp resume_userspace"
: /* no outputs */
- :"r" (&info->regs), "r" (task_thread_info(tsk)), "r" (0));
+ :"r" (&info->regs), "r" (task_thread_info(tsk)));
/* we never return here */
}

--
"Excuse all the blood" -- Dead



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