uprobes/x86: Emulate nop's using ops->emulate()

Finally we can kill the ugly (and very limited) code in __skip_sstep().
Just change branch_setup_xol_ops() to treat "nop" as jmp to the next insn.

Thanks to lib/insn.c, it is clever enough. OPCODE1() == 0x90 includes
"(rep;)+ nop;" at least, and (afaics) much more.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jim Keniston <jkenisto@us.ibm.com>

1 files changed, 1 insertions, 19 deletions

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index c3baeaacf1b6..f3c4212f3819 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -478,6 +478,7 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
         switch (OPCODE1(insn)) {
         case 0xeb:      /* jmp 8 */
         case 0xe9:      /* jmp 32 */
+        case 0x90:      /* prefix* + nop; same as jmp with .offs = 0 */
                 break;
         default:
                 return -ENOSYS;
@@ -710,29 +711,10 @@ void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
                 regs->flags &= ~X86_EFLAGS_TF;
 }
 
-/*
- * Skip these instructions as per the currently known x86 ISA.
- * rep=0x66*; nop=0x90
- */
 static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {
-        int i;
-
         if (auprobe->ops->emulate)
                 return auprobe->ops->emulate(auprobe, regs);
-
-        /* TODO: move this code into ->emulate() hook */
-        for (i = 0; i < MAX_UINSN_BYTES; i++) {
-                if (auprobe->insn[i] == 0x66)
-                        continue;
-
-                if (auprobe->insn[i] == 0x90) {
-                        regs->ip += i + 1;
-                        return true;
-                }
-
-                break;
-        }
         return false;
 }