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Subject[RFC PATCH v2 5/6] uprobes/x86: Emulate rip-relative conditional "short" jmp's
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@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
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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