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Message-Id: <20180829090832.337553da18089643a107cf56@kernel.org>
Date: Wed, 29 Aug 2018 09:08:32 +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 2/7] x86: inline kprobe_exceptions_notify() into
do_general_protection()
On Tue, 28 Aug 2018 22:14:16 +0200
Jann Horn <jannh@...gle.com> wrote:
> The opaque plumbing of #GP from do_general_protection() through
> notify_die() into kprobe_exceptions_notify() makes it hard to understand
> what's going on.
OK, this seems reasonable optimization, since kprobe_exceptions_notify
only handles DIE_GPF now.
Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
Hmm, I think I should introduce ARCH_KPROBE_HANDLE_EXCEPTION and if it
is enabled, kernel/kprobes.c stops using exception notifier. It is
no more needed on x86.
Thank you!
>
> Suggested-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Jann Horn <jannh@...gle.com>
> ---
> arch/x86/kernel/kprobes/core.c | 31 +------------------------------
> arch/x86/kernel/traps.c | 10 ++++++++++
> 2 files changed, 11 insertions(+), 30 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index b0d1e81c96bb..467ac22691b0 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -1028,42 +1028,13 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
> if (fixup_exception(regs, trapnr))
> return 1;
>
> - /*
> - * fixup routine could not handle it,
> - * Let do_page_fault() fix it.
> - */
> + /* fixup routine could not handle it. */
> }
>
> return 0;
> }
> NOKPROBE_SYMBOL(kprobe_fault_handler);
>
> -/*
> - * Wrapper routine for handling exceptions.
> - */
> -int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val,
> - void *data)
> -{
> - struct die_args *args = data;
> - int ret = NOTIFY_DONE;
> -
> - if (args->regs && user_mode(args->regs))
> - return ret;
> -
> - if (val == DIE_GPF) {
> - /*
> - * To be potentially processing a kprobe fault and to
> - * trust the result from kprobe_running(), we have
> - * be non-preemptible.
> - */
> - if (!preemptible() && kprobe_running() &&
> - kprobe_fault_handler(args->regs, args->trapnr))
> - ret = NOTIFY_STOP;
> - }
> - return ret;
> -}
> -NOKPROBE_SYMBOL(kprobe_exceptions_notify);
> -
> bool arch_within_kprobe_blacklist(unsigned long addr)
> {
> bool is_in_entry_trampoline_section = false;
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index e6db475164ed..bf9ab1aaa175 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -556,6 +556,16 @@ do_general_protection(struct pt_regs *regs, long error_code)
>
> tsk->thread.error_code = error_code;
> tsk->thread.trap_nr = X86_TRAP_GP;
> +
> + /*
> + * To be potentially processing a kprobe fault and to
> + * trust the result from kprobe_running(), we have to
> + * be non-preemptible.
> + */
> + if (!preemptible() && kprobe_running() &&
> + kprobe_fault_handler(regs, X86_TRAP_GP))
> + return;
> +
> if (notify_die(DIE_GPF, "general protection fault", regs, error_code,
> X86_TRAP_GP, SIGSEGV) != NOTIFY_STOP)
> die("general protection fault", regs, error_code);
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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