kprobes/x86: Fix page-fault handling logic
authorMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Thu, 17 Apr 2014 08:16:44 +0000 (17:16 +0900)
committerIngo Molnar <mingo@kernel.org>
Thu, 17 Apr 2014 08:57:02 +0000 (10:57 +0200)
commit6381c24cd6d5d6373620426ab0a96c80ed953e20
tree1ec21edeac1c0d940b35689ae79f45e95c7a4d7f
parent6ca2a88ad820af56535ed1e6936e0490cb6ec6dc
kprobes/x86: Fix page-fault handling logic

Current kprobes in-kernel page fault handler doesn't
expect that its single-stepping can be interrupted by
an NMI handler which may cause a page fault(e.g. perf
with callback tracing).

In that case, the page-fault handled by kprobes and it
misunderstands the page-fault has been caused by the
single-stepping code and tries to recover IP address
to probed address.

But the truth is the page-fault has been caused by the
NMI handler, and do_page_fault failes to handle real
page fault because the IP address is modified and
causes Kernel BUGs like below.

 ----
 [ 2264.726905] BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
 [ 2264.727190] IP: [<ffffffff813c46e0>] copy_user_generic_string+0x0/0x40

To handle this correctly, I fixed the kprobes fault
handler to ensure the faulted ip address is its own
single-step buffer instead of checking current kprobe
state.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: fche@redhat.com
Cc: systemtap@sourceware.org
Link: http://lkml.kernel.org/r/20140417081644.26341.52351.stgit@ltc230.yrl.intra.hitachi.co.jp
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arch/x86/kernel/kprobes/core.c