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Date: Wed, 29 Aug 2018 08:32:24 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Jann Horn <jannh@...gle.com>
Cc: 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,
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: Re: [PATCH v3 1/7] x86: refactor kprobes_fault() like
kprobe_exceptions_notify()
On Tue, 28 Aug 2018 22:14:15 +0200
Jann Horn <jannh@...gle.com> wrote:
> 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.
Good catch!
Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
Thanks!
> + */
> + if (preemptible())
> + return 0;
> + if (!kprobe_running())
> + return 0;
> + return kprobe_fault_handler(regs, X86_TRAP_PF);
> }
>
> /*
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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