linux-kernel - [PATCH v2 3.16] x86,kprobes: Don't try to resolve kprobe faults from userspace

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Message-Id: <c4e339882c121aa76254f2adde3fcbdf502faec2.1405099506.git.luto@amacapital.net>
Date:	Fri, 11 Jul 2014 10:27:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Andy Lutomirski <luto@...capital.net>
Subject: [PATCH v2 3.16] x86,kprobes: Don't try to resolve kprobe faults from userspace

This commit:

    commit 6f6343f53d133bae516caf3d254bce37d8774625
    Author: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
    Date:   Thu Apr 17 17:17:33 2014 +0900

        kprobes/x86: Call exception handlers directly from do_int3/do_debug

appears to have inadvertently dropped a check that the int3 came
from kernel mode.  Trying to dereference addr when addr is
user-controlled is completely bogus.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
---

Changes from v1: Fixed the changelog message

 arch/x86/kernel/kprobes/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 7596df6..67e6d19 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -574,6 +574,9 @@ int kprobe_int3_handler(struct pt_regs *regs)
 	struct kprobe *p;
 	struct kprobe_ctlblk *kcb;
 
+	if (user_mode_vm(regs))
+		return 0;
+
 	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
 	/*
 	 * We don't want to be preempted for the entire
-- 
1.9.3

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