[PATCH for review] [83/145] x86_64: fix is_at_popf() for compat tasks

[Andi Kleen]

r

From: Chuck Ebbert <76306.1226@xxxxxxxxxxxxxx>

When testing for the REX instruction prefix, first check
for 32-bit mode because in compat mode the REX prefix is an
increment instruction.

Signed-off-by: Chuck Ebbert <76306.1226@xxxxxxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxx>

---
 arch/x86_64/kernel/ptrace.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletion(-)

Index: linux/arch/x86_64/kernel/ptrace.c
===================================================================
--- linux.orig/arch/x86_64/kernel/ptrace.c
+++ linux/arch/x86_64/kernel/ptrace.c
@@ -141,8 +141,11 @@ static int is_at_popf(struct task_struct
 		case 0xf0: case 0xf2: case 0xf3:
 			continue;
 
-		/* REX prefixes */
 		case 0x40 ... 0x4f:
+			if (regs->cs != __USER_CS)
+				/* 32-bit mode: register increment */
+				return 0;
+			/* 64-bit mode: REX prefix */
 			continue;
 
 			/* CHECKME: f0, f2, f3 */
-
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