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Message-Id: <20180828201421.157735-2-jannh@google.com>
Date: Tue, 28 Aug 2018 22:14:15 +0200
From: Jann Horn <jannh@...gle.com>
To: Kees Cook <keescook@...omium.org>, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
kernel-hardening@...ts.openwall.com, jannh@...gle.com
Cc: linux-kernel@...r.kernel.org, dvyukov@...gle.com,
Masami Hiramatsu <mhiramat@...nel.org>, "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>, "David S. Miller" <davem@...emloft.net>,
Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
Borislav Petkov <bp@...en8.de>
Subject: [PATCH v3 1/7] x86: 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, you don't have to
disable preemption - if preemption is on, you can't be in a kprobe.
Also, use X86_TRAP_PF instead of 14.
Signed-off-by: Jann Horn <jannh@...gle.com>
---
v3:
- avoid unnecessary branch on return value and split up the checks
(Borislav Petkov)
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 b9123c497e0a..bcdaae1d5bf5 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);
}
/*
--
2.19.0.rc0.228.g281dcd1b4d0-goog
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