[RFC PATCH v2 5/6] uprobes/x86: Emulate rip-relative conditional "short" jmp's

[Oleg Nesterov]

On 04/06, Oleg Nesterov wrote:
>
> Incomplete, lacks "jcxz". Simple to fix. Anything else?

Please see v2 below. Simplify the preprocessor hacks.

-------------------------------------------------------------------------------
Subject: [RFC PATCH v2 5/6] uprobes/x86: Emulate rip-relative conditional "short" jmp's

Incomplete, lacks "jcxz". Simple to fix. Anything else?

Reported-by: Jonathan Lebon <jlebon@xxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 arch/x86/kernel/uprobes.c |   61 +++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 9283024..3865d8b 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -466,18 +466,72 @@ static bool ttt_is_call(struct arch_uprobe *auprobe)
 	return auprobe->ttt.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->ttt.opc1) {
+	case 0x00:	/* not a conditional jmp */
+		return true;
+
+	#define DO(expr)	\
+		return expr;
+	CASE_COND
+	#undef	DO
+
+	default:
+		BUG();
+	}
+}
+
+#undef	XF
+#undef	COND
+#undef	CASE_COND
+
 static bool ttt_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {
 	unsigned long new_ip = regs->ip += auprobe->ttt.ilen;
+	unsigned long disp = auprobe->ttt.disp;
 
 	if (ttt_is_call(auprobe)) {
 		unsigned long new_sp = regs->sp - sizeof_long();
 		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)) {
+		disp = 0;
 	}
 
-	regs->ip = new_ip + auprobe->ttt.disp;
+	regs->ip = new_ip + disp;
 	return true;
 }
 
@@ -536,8 +590,11 @@ static int ttt_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 		ttt_clear_displacement(auprobe, insn);
 		auprobe->ttt.opc1 = opc1;
 		break;
+
 	default:
-		return -ENOSYS;
+		if (!is_cond_jmp_opcode(opc1))
+			return -ENOSYS;
+		auprobe->ttt.opc1 = opc1;
 	}
 
 	auprobe->ttt.ilen = insn->length;
-- 
1.5.5.1


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