From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 75134C4345F for ; Mon, 29 Apr 2024 13:49:01 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=lyORC9o2; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4VSl6h0hfdz3cll for ; Mon, 29 Apr 2024 23:49:00 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=lyORC9o2; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=145.40.73.55; helo=sin.source.kernel.org; envelope-from=mhiramat@kernel.org; receiver=lists.ozlabs.org) Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4VSl5q67hWz3cVq for ; Mon, 29 Apr 2024 23:48:15 +1000 (AEST) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sin.source.kernel.org (Postfix) with ESMTP id 7009ACE0B94; Mon, 29 Apr 2024 13:48:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 427D1C113CD; Mon, 29 Apr 2024 13:48:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1714398492; bh=2OmxYBcG8kYWa15/HKPOVgxwdgSzJ8/xMevqt/hqwIo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=lyORC9o2Lm+u2avM+eOyj/ccYiyuxZQLnwqOF6FZV49QnzRN+Dcvvb8f+L/I+DIcc bR6gzWrxR06bLVpEA1X1PfPHzCF0nDSdsFIGgv/R/Ztx7jvyn/LZvp5GTSxbA3X+Ea 5Q5++mVTUse/so5L++FV3pac1nAd6FyimPuc/dQPplc7m0nyf+JoSS48zL0c07gOKG +Q9TxDTXUAv++YZPpMLvDQVzMH1VHt+BXIScwupTc1u15EnhRP870WSg23oHheSEFh X/E2DhZuUkcbr1ov6EZLQFmBffBmxl2jf1fX5T3O6khvfYPOQWnrKD7j3rIrd7dwdJ AMHlyJcx5ffMw== Date: Mon, 29 Apr 2024 22:48:03 +0900 From: Masami Hiramatsu (Google) To: Stephen Brennan Subject: Re: [PATCH] kprobe/ftrace: bail out if ftrace was killed Message-Id: <20240429224803.49d420b514e22d51412e1602@kernel.org> In-Reply-To: <20240426225834.993353-1-stephen.s.brennan@oracle.com> References: <20240426225834.993353-1-stephen.s.brennan@oracle.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , x86@kernel.org, Dave Hansen , "James E.J. Bottomley" , Guo Ren , linux-csky@vger.kernel.org, "H. Peter Anvin" , Alexander Gordeev , WANG Xuerui , linux-s390@vger.kernel.org, Helge Deller , Huacai Chen , "Aneesh Kumar K.V" , Ingo Molnar , "Naveen N. Rao" , Christian Borntraeger , linux-trace-kernel@vger.kernel.org, Albert Ou , Vasily Gorbik , Heiko Carstens , Steven Rostedt , Borislav Petkov , Nicholas Piggin , loongarch@lists.linux.dev, Paul Walmsley , Thomas Gleixner , linux-parisc@vger.kernel.org, linux-kern el@vger.kernel.org, linux-riscv@lists.infradead.org, Palmer Dabbelt , Sven Schnelle , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Stephen, On Fri, 26 Apr 2024 15:58:34 -0700 Stephen Brennan wrote: > If an error happens in ftrace, ftrace_kill() will prevent disarming > kprobes. Eventually, the ftrace_ops associated with the kprobes will be > freed, yet the kprobes will still be active, and when triggered, they > will use the freed memory, likely resulting in a page fault and panic. Hmm, indeed. > > This behavior can be reproduced quite easily, by creating a kprobe and > then triggering a ftrace_kill(). For simplicity, we can simulate an > ftrace error with a kernel module like [1]: > > [1]: https://github.com/brenns10/kernel_stuff/tree/master/ftrace_killer > > sudo perf probe --add commit_creds > sudo perf trace -e probe:commit_creds > # In another terminal > make > sudo insmod ftrace_killer.ko # calls ftrace_kill(), simulating bug > # Back to perf terminal > # ctrl-c > sudo perf probe --del commit_creds > > After a short period, a page fault and panic would occur as the kprobe > continues to execute and uses the freed ftrace_ops. While ftrace_kill() > is supposed to be used only in extreme circumstances, it is invoked in > FTRACE_WARN_ON() and so there are many places where an unexpected bug > could be triggered, yet the system may continue operating, possibly > without the administrator noticing. If ftrace_kill() does not panic the > system, then we should do everything we can to continue operating, > rather than leave a ticking time bomb. OK, the patch looks good to me. Acked-by: Masami Hiramatsu (Google) Thanks! > > Signed-off-by: Stephen Brennan > --- > > Apologies for the wide net cast here. I recognize that a change like this > may need to be split up and go through arch-specific trees. I hoped to get > feedback on the patch itself. If it's satisfactory and the architecture > maintainers prefer it split out, I'm glad to do it. Thanks! > > arch/csky/kernel/probes/ftrace.c | 3 +++ > arch/loongarch/kernel/ftrace_dyn.c | 3 +++ > arch/parisc/kernel/ftrace.c | 3 +++ > arch/powerpc/kernel/kprobes-ftrace.c | 3 +++ > arch/riscv/kernel/probes/ftrace.c | 3 +++ > arch/s390/kernel/ftrace.c | 3 +++ > arch/x86/kernel/kprobes/ftrace.c | 3 +++ > include/linux/ftrace.h | 2 ++ > 8 files changed, 23 insertions(+) > > diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c > index 834cffcfbce3..3931bf9f707b 100644 > --- a/arch/csky/kernel/probes/ftrace.c > +++ b/arch/csky/kernel/probes/ftrace.c > @@ -12,6 +12,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > struct kprobe_ctlblk *kcb; > struct pt_regs *regs; > > + if (unlikely(ftrace_is_dead())) > + return; > + > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > return; > diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c > index 73858c9029cc..82c952cb5be0 100644 > --- a/arch/loongarch/kernel/ftrace_dyn.c > +++ b/arch/loongarch/kernel/ftrace_dyn.c > @@ -287,6 +287,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > struct kprobe *p; > struct kprobe_ctlblk *kcb; > > + if (unlikely(ftrace_is_dead())) > + return; > + > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > return; > diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c > index 621a4b386ae4..3660834f54c3 100644 > --- a/arch/parisc/kernel/ftrace.c > +++ b/arch/parisc/kernel/ftrace.c > @@ -206,6 +206,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > struct kprobe *p; > int bit; > > + if (unlikely(ftrace_is_dead())) > + return; > + > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > return; > diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c > index 072ebe7f290b..85eb55aa1457 100644 > --- a/arch/powerpc/kernel/kprobes-ftrace.c > +++ b/arch/powerpc/kernel/kprobes-ftrace.c > @@ -21,6 +21,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, > struct pt_regs *regs; > int bit; > > + if (unlikely(ftrace_is_dead())) > + return; > + > bit = ftrace_test_recursion_trylock(nip, parent_nip); > if (bit < 0) > return; > diff --git a/arch/riscv/kernel/probes/ftrace.c b/arch/riscv/kernel/probes/ftrace.c > index 7142ec42e889..8814fbe4c888 100644 > --- a/arch/riscv/kernel/probes/ftrace.c > +++ b/arch/riscv/kernel/probes/ftrace.c > @@ -11,6 +11,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > struct kprobe_ctlblk *kcb; > int bit; > > + if (unlikely(ftrace_is_dead())) > + return; > + > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > return; > diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c > index c46381ea04ec..ccbe8ccf945b 100644 > --- a/arch/s390/kernel/ftrace.c > +++ b/arch/s390/kernel/ftrace.c > @@ -296,6 +296,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > struct kprobe *p; > int bit; > > + if (unlikely(ftrace_is_dead())) > + return; > + > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > return; > diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c > index dd2ec14adb77..c73f9ab7ff50 100644 > --- a/arch/x86/kernel/kprobes/ftrace.c > +++ b/arch/x86/kernel/kprobes/ftrace.c > @@ -21,6 +21,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > struct kprobe_ctlblk *kcb; > int bit; > > + if (unlikely(ftrace_is_dead())) > + return; > + > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > return; > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index 54d53f345d14..ba83e99c1fbe 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -399,6 +399,7 @@ int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *a > #define register_ftrace_function(ops) ({ 0; }) > #define unregister_ftrace_function(ops) ({ 0; }) > static inline void ftrace_kill(void) { } > +static inline int ftrace_is_dead(void) { return 0; } > static inline void ftrace_free_init_mem(void) { } > static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { } > static inline int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs) > @@ -914,6 +915,7 @@ static inline bool is_ftrace_trampoline(unsigned long addr) > > /* totally disable ftrace - can not re-enable after this */ > void ftrace_kill(void); > +int ftrace_is_dead(void); > > static inline void tracer_disable(void) > { > -- > 2.39.3 > -- Masami Hiramatsu (Google)