[tip:perf/urgent] kprobes/x86: Don' t try to resolve kprobe faults from userspace

[tip-bot for Andy Lutomirski <tipbot@zytor.com>]

Commit-ID:  0cdd192cf40fb6dbf03ec3af1c670068de3fd26c
Gitweb:     http://git.kernel.org/tip/0cdd192cf40fb6dbf03ec3af1c670068de3fd26c
Author:     Andy Lutomirski <luto@amacapital.net>
AuthorDate: Fri, 11 Jul 2014 10:27:01 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 16 Jul 2014 14:16:32 +0200

kprobes/x86: Don't try to resolve kprobe faults from userspace

This commit:

    commit 6f6343f53d133bae516caf3d254bce37d8774625
    Author: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.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@amacapital.net>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Link: http://lkml.kernel.org/r/c4e339882c121aa76254f2adde3fcbdf502faec2.1405099506.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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