[PATCH] x86 : Ensure X86_FLAGS_NT is cleared on syscall entry

[Anish Bhatt <anish@chelsio.com>]

The MSR_SYSCALL_MASK, which is responsible for clearing specific EFLAGS on
 syscall entry, should also clear the nested task (NT) flag to be safe from
 userspace injection. Without this fix the application segmentation
 faults on syscall return because of the changed meaning of the IRET
 instruction.

Further details can be seen here https://bugs.winehq.org/show_bug.cgi?id=33275

Signed-off-by: Anish Bhatt <anish@chelsio.com>
Signed-off-by: Sebastian Lackner <sebastian@fds-team.de>
---
 arch/x86/kernel/cpu/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index e4ab2b4..3126558 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1184,7 +1184,7 @@ void syscall_init(void)
 	/* Flags to clear on syscall */
 	wrmsrl(MSR_SYSCALL_MASK,
 	       X86_EFLAGS_TF|X86_EFLAGS_DF|X86_EFLAGS_IF|
-	       X86_EFLAGS_IOPL|X86_EFLAGS_AC);
+	       X86_EFLAGS_IOPL|X86_EFLAGS_AC|X86_EFLAGS_NT);
 }
 
 /*
-- 
2.1.0