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Subject[tip:x86/core] x86/kprobes: Refactor kprobes_fault() like kprobe_exceptions_notify()
Commit-ID:  a980c0ef9f6d8c45445d6ed0f5836bb6941c8c91
Gitweb: https://git.kernel.org/tip/a980c0ef9f6d8c45445d6ed0f5836bb6941c8c91
Author: Jann Horn <jannh@google.com>
AuthorDate: Tue, 28 Aug 2018 22:14:15 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Mon, 3 Sep 2018 15:12:08 +0200

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

---
arch/x86/mm/fault.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 47bebfe6efa7..d99edb2d567b 100644
--- 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);
}

/*
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