From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3076F12B77; Thu, 2 May 2024 02:03:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714615439; cv=none; b=aaNfuZr2OQygb6L5OKhl96mE/D/DYJOT3YSiLEvc6mGxia6KkMXQqYLWeFh/yUwR0/hYmryWl8UkTUwpn2PoXOW4ihhbrjRe6YU5UtsE9/RauoChT3oEBZAXi8Yp75Cpv0DYgir5UU16cVnY08uHLndrlbfBRE4dOdSelrdTneU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714615439; c=relaxed/simple; bh=SWeXBcXKkGPsnHoi2Nzn5QOh0E73YoSqFU3TTZEHOKs=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=VFdvo6Nb7AKdr0TQYrnBYF0N6n7MQfZrs40UoLktR9ERl2an9LskQjXP01mBIZeeiDjCKsIC9S8id3oiHjNup3CBX5LejFeE+Pn/ZuYHHAHW3HoGEaRzqgoclh87dlbir5CNyWPFD+xK3jdhe7iHMfHx4m5OxRjscxeZkQmQAaA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YhQIcLda; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YhQIcLda" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 61933C072AA; Thu, 2 May 2024 02:03:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1714615438; bh=SWeXBcXKkGPsnHoi2Nzn5QOh0E73YoSqFU3TTZEHOKs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=YhQIcLdaveuK6MKu9y1bDPu7YCeJeaD5GJ35EMerY6iX3OsYP+KVxeTI+M0gEZQbs LxO+v7yucUYCdXnMxtB2jBZe6xTl6o61vJb4R2yUuZlI/0AvHG4TY/VVikUFRSux50 gw3mNFE5e07MSAqwmvg1EXJyNPHjPdJqheM8nxMdWoU/Azn6W5Byp3CMODzXHf3s9a /k+7PeaHHzE+y6eRMY8KPhYObFbk091HF3G+gVHvMmPrvMWxWX+UJkO/5YwSlsLYsF fsEtpqtSpMPA2EkSrwsyNkC/Fuc86iYSQS6bdNM2fAroRhz83u1/uEGQo3Hv5h3uG0 90V/Mvci7IfiA== Date: Thu, 2 May 2024 11:03:48 +0900 From: Masami Hiramatsu (Google) To: Guo Ren Cc: Stephen Brennan , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Huacai Chen , WANG Xuerui , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-csky@vger.kernel.org, loongarch@lists.linux.dev, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org Subject: Re: [PATCH v3] kprobe/ftrace: bail out if ftrace was killed Message-Id: <20240502110348.016f190e0b0565b7e9ecdb48@kernel.org> In-Reply-To: References: <20240501162956.229427-1-stephen.s.brennan@oracle.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-csky@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Thu, 2 May 2024 01:35:16 +0800 Guo Ren wrote: > On Thu, May 2, 2024 at 12:30 AM 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. > > > > 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. > > > > Signed-off-by: Stephen Brennan > > --- > > Changes in v3: > > Don't expose ftrace_is_dead(). Create a "kprobe_ftrace_disabled" > > variable and check it directly in the kprobe handlers. > > Link to v1/v2 discussion: > > https://lore.kernel.org/all/20240426225834.993353-1-stephen.s.brennan@oracle.com/ > > > > 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/kprobes.h | 7 +++++++ > > kernel/kprobes.c | 6 ++++++ > > kernel/trace/ftrace.c | 1 + > > 10 files changed, 35 insertions(+) > > > > diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c > > index 834cffcfbce3..7ba4b98076de 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(kprobe_ftrace_disabled)) > > + return; > > + > For csky part. > Acked-by: Guo Ren Thanks Stephen, Guo and Steve! Let me pick this to probes/for-next! Thank you, > > > 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..bff058317062 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(kprobe_ftrace_disabled)) > > + 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..c91f9c2e61ed 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(kprobe_ftrace_disabled)) > > + 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..f8208c027148 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(kprobe_ftrace_disabled)) > > + 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..a69dfa610aa8 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(kprobe_ftrace_disabled)) > > + 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..7f6f8c438c26 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(kprobe_ftrace_disabled)) > > + 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..15af7e98e161 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(kprobe_ftrace_disabled)) > > + return; > > + > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > > if (bit < 0) > > return; > > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h > > index 0ff44d6633e3..5fcbc254d186 100644 > > --- a/include/linux/kprobes.h > > +++ b/include/linux/kprobes.h > > @@ -378,11 +378,15 @@ static inline void wait_for_kprobe_optimizer(void) { } > > extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > struct ftrace_ops *ops, struct ftrace_regs *fregs); > > extern int arch_prepare_kprobe_ftrace(struct kprobe *p); > > +/* Set when ftrace has been killed: kprobes on ftrace must be disabled for safety */ > > +extern bool kprobe_ftrace_disabled __read_mostly; > > +extern void kprobe_ftrace_kill(void); > > #else > > static inline int arch_prepare_kprobe_ftrace(struct kprobe *p) > > { > > return -EINVAL; > > } > > +static inline void kprobe_ftrace_kill(void) {} > > #endif /* CONFIG_KPROBES_ON_FTRACE */ > > > > /* Get the kprobe at this addr (if any) - called with preemption disabled */ > > @@ -495,6 +499,9 @@ static inline void kprobe_flush_task(struct task_struct *tk) > > static inline void kprobe_free_init_mem(void) > > { > > } > > +static inline void kprobe_ftrace_kill(void) > > +{ > > +} > > static inline int disable_kprobe(struct kprobe *kp) > > { > > return -EOPNOTSUPP; > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > index 65adc815fc6e..166ebf81dc45 100644 > > --- a/kernel/kprobes.c > > +++ b/kernel/kprobes.c > > @@ -1068,6 +1068,7 @@ static struct ftrace_ops kprobe_ipmodify_ops __read_mostly = { > > > > static int kprobe_ipmodify_enabled; > > static int kprobe_ftrace_enabled; > > +bool kprobe_ftrace_disabled; > > > > static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops, > > int *cnt) > > @@ -1136,6 +1137,11 @@ static int disarm_kprobe_ftrace(struct kprobe *p) > > ipmodify ? &kprobe_ipmodify_ops : &kprobe_ftrace_ops, > > ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled); > > } > > + > > +void kprobe_ftrace_kill() > > +{ > > + kprobe_ftrace_disabled = true; > > +} > > #else /* !CONFIG_KPROBES_ON_FTRACE */ > > static inline int arm_kprobe_ftrace(struct kprobe *p) > > { > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > > index da1710499698..96db99c347b3 100644 > > --- a/kernel/trace/ftrace.c > > +++ b/kernel/trace/ftrace.c > > @@ -7895,6 +7895,7 @@ void ftrace_kill(void) > > ftrace_disabled = 1; > > ftrace_enabled = 0; > > ftrace_trace_function = ftrace_stub; > > + kprobe_ftrace_kill(); > > } > > > > /** > > -- > > 2.39.3 > > > > > -- > Best Regards > Guo Ren -- Masami Hiramatsu (Google)