fix is_at_popf() for compat tasks From: Chuck Ebbert <76306.1226@compuserve.com> 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@compuserve.com> Signed-off-by: Andi Kleen --- arch/x86_64/kernel/ptrace.c | 5 ++++- 1 file 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 */