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>

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 7596df6..67e6d19 100644 (file)
--- 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