uprobes/x86: Emulate relative conditional "near" jmp's

Change branch_setup_xol_ops() to simply use opc1 = OPCODE2(insn) - 0x10
if OPCODE1() == 0x0f; this matches the "short" jmp which checks the same
condition.

Thanks to lib/insn.c, it does the rest correctly. branch->ilen/offs are
correct no matter if this jmp is "near" or "short".

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

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 0460d04f0acc..ace22916ade3 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -599,6 +599,14 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
                 branch_clear_offset(auprobe, insn);
                 break;
 
+        case 0x0f:
+                if (insn->opcode.nbytes != 2)
+                        return -ENOSYS;
+                /*
+                 * If it is a "near" conditional jmp, OPCODE2() - 0x10 matches
+                 * OPCODE1() of the "short" jmp which checks the same condition.
+                 */
+                opc1 = OPCODE2(insn) - 0x10;
         default:
                 if (!is_cond_jmp_opcode(opc1))
                         return -ENOSYS;