[PATCH 3.19 1/3] x86, mpx: Check user mode bitness correctly when decoding instructions

[Andy Lutomirski]

When decoding a user instruction, the bitness depends on CS, not on
TIF_IA32.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
 arch/x86/include/asm/ptrace.h | 5 +++++
 arch/x86/mm/mpx.c             | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 86fc2bb82287..189113c74726 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -144,6 +144,11 @@ static inline bool user_64bit_mode(struct pt_regs *regs)
 	(test_thread_flag(TIF_IA32) 	\
 	 ? current_pt_regs()->sp 	\
 	 : this_cpu_read(old_rsp))
+#else
+static inline bool user_64bit_mode(struct pt_regs *regs)
+{
+	return false;
+}
 #endif
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 67ebf5751222..082ab9c4ac1c 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -217,7 +217,7 @@ static int mpx_insn_decode(struct insn *insn,
 			   struct pt_regs *regs)
 {
 	unsigned char buf[MAX_INSN_SIZE];
-	int x86_64 = !test_thread_flag(TIF_IA32);
+	int x86_64 = user_64bit_mode(regs);
 	int not_copied;
 	int nr_copied;
 
-- 
2.1.0

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