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

Teach branch_emulate_op() to emulate the conditional "short" jmp's which
check regs->flags.

Note: this doesn't support jcxz/jcexz, loope/loopz, and loopne/loopnz.
They all are rel8 and thus they can't trigger the problem, but perhaps
we will add the support in future just for completeness.

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

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 0914435..0460d04 100644 (file)
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -466,9 +466,58 @@ static bool branch_is_call(struct arch_uprobe *auprobe)
        return auprobe->branch.opc1 == 0xe8;
 }
 
+#define CASE_COND                                      \
+       COND(70, 71, XF(OF))                            \
+       COND(72, 73, XF(CF))                            \
+       COND(74, 75, XF(ZF))                            \
+       COND(78, 79, XF(SF))                            \
+       COND(7a, 7b, XF(PF))                            \
+       COND(76, 77, XF(CF) || XF(ZF))                  \
+       COND(7c, 7d, XF(SF) != XF(OF))                  \
+       COND(7e, 7f, XF(ZF) || XF(SF) != XF(OF))
+
+#define COND(op_y, op_n, expr)                         \
+       case 0x ## op_y: DO((expr) != 0)                \
+       case 0x ## op_n: DO((expr) == 0)
+
+#define XF(xf) (!!(flags & X86_EFLAGS_ ## xf))
+
+static bool is_cond_jmp_opcode(u8 opcode)
+{
+       switch (opcode) {
+       #define DO(expr)        \
+               return true;
+       CASE_COND
+       #undef  DO
+
+       default:
+               return false;
+       }
+}
+
+static bool check_jmp_cond(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+       unsigned long flags = regs->flags;
+
+       switch (auprobe->branch.opc1) {
+       #define DO(expr)        \
+               return expr;
+       CASE_COND
+       #undef  DO
+
+       default:        /* not a conditional jmp */
+               return true;
+       }
+}
+
+#undef XF
+#undef COND
+#undef CASE_COND
+
 static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {
        unsigned long new_ip = regs->ip += auprobe->branch.ilen;
+       unsigned long offs = (long)auprobe->branch.offs;
 
        if (branch_is_call(auprobe)) {
                unsigned long new_sp = regs->sp - sizeof_long();
@@ -484,9 +533,11 @@ static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
                if (copy_to_user((void __user *)new_sp, &new_ip, sizeof_long()))
                        return false;
                regs->sp = new_sp;
+       } else if (!check_jmp_cond(auprobe, regs)) {
+               offs = 0;
        }
 
-       regs->ip = new_ip + auprobe->branch.offs;
+       regs->ip = new_ip + offs;
        return true;
 }
 
@@ -547,8 +598,10 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
        case 0xe8:      /* call relative */
                branch_clear_offset(auprobe, insn);
                break;
+
        default:
-               return -ENOSYS;
+               if (!is_cond_jmp_opcode(opc1))
+                       return -ENOSYS;
        }
 
        auprobe->branch.opc1 = opc1;