x86/kprobes: Refactor kprobes_fault() like kprobe_exceptions_notify()

This is an extension of commit b506a9d08bae ("x86: code clarification patch
to Kprobes arch code"). As that commit explains, even though
kprobe_running() can't be called with preemption enabled, preemption does
not need to be disabled. If preemption is enabled, then this can't be
originate from a kprobe.

Also, use X86_TRAP_PF instead of 14.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Kees Cook <keescook@chromium.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: kernel-hardening@lists.openwall.com
Cc: dvyukov@google.com
Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Link: https://lkml.kernel.org/r/20180828201421.157735-2-jannh@google.com

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 47bebfe6efa70a316424934683f4302de33876a2..d99edb2d567b8c487e13105616114aae3333dd58 100644 (file)
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -44,17 +44,19 @@ kmmio_fault(struct pt_regs *regs, unsigned long addr)
 
 static nokprobe_inline int kprobes_fault(struct pt_regs *regs)
 {
-       int ret = 0;
-
-       /* kprobe_running() needs smp_processor_id() */
-       if (kprobes_built_in() && !user_mode(regs)) {
-               preempt_disable();
-               if (kprobe_running() && kprobe_fault_handler(regs, 14))
-                       ret = 1;
-               preempt_enable();
-       }
-
-       return ret;
+       if (!kprobes_built_in())
+               return 0;
+       if (user_mode(regs))
+               return 0;
+       /*
+        * To be potentially processing a kprobe fault and to be allowed to call
+        * kprobe_running(), we have to be non-preemptible.
+        */
+       if (preemptible())
+               return 0;
+       if (!kprobe_running())
+               return 0;
+       return kprobe_fault_handler(regs, X86_TRAP_PF);
 }
 
 /*