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 3285B1877; Thu, 16 May 2024 00:24:05 +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=1715819046; cv=none; b=V/TIrWS3SwCcMSfMryZJ4Q64BlJjUobYFyQGbteHtMPbaeKF/DB7JC4tQp3pwcP4hrHK9/bKsHTCYimQ5lkEOaAkhnmJyyDXhsr5K/kUN4coeb0Uob0O7ZcSKlFKOm/BaklkchzUj70t0hqUZMON349WufcAHNC/WcSMxtK6N08= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715819046; c=relaxed/simple; bh=2mTyV3yHsXnpIz+Hf8dHwdpSsS9bL76Nasiv3NlJOGU=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=l1QI9khiLElR7VFjzE5or0yCKtQTm1UPHdHFUtG8qZM/wRHYZZaRZmRraCJx+an6l6BO1PV8A6GVEiqLQm20tEPYY995CkuIwhIYYNEczIM7+014gTqnGq+xOz5amnD7OukLZYAwkx/JrjT1pmJKQRzhBrH86B3fx+r4YzJTjj0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eyhYvQrh; 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="eyhYvQrh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34B95C116B1; Thu, 16 May 2024 00:23:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1715819045; bh=2mTyV3yHsXnpIz+Hf8dHwdpSsS9bL76Nasiv3NlJOGU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=eyhYvQrhNljUOqI7QNUxGGddgXbxg9y2eAf3SrTd+rZn8BqfPQoiuSPf3cJR34dYa zSvce/f+OH48w4hBDOW3RJtYyeJg/nH46JmYm2E1PnSRHy3kF0o/T3lOVha7lvTJZL uwq0IQjHw/2eZmSVpTKVdnQCl4UR4thsmYHeiq/1GVjfoMBQqd3nuLCklTZ9PM9S84 D8LoRdc+cO+u2c30aTUmBWeafhneREBkpHfzgJUF++utFsobb1GHqqrDGDR8WHyFxG uiknNVRd2iWPJ5aH2ELN/FibJPqRnrW3ba5PPk+Mf7re8cp/Bm8sj9dFC7CoxlOg4B VDJeBnkbZygiA== Date: Thu, 16 May 2024 09:23:55 +0900 From: Masami Hiramatsu (Google) To: Stephen Brennan Cc: Guo Ren , Steven Rostedt , 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: <20240516092355.4eaab560b7f4e22953f73cfc@kernel.org> In-Reply-To: <87r0e2pvmn.fsf@oracle.com> References: <20240501162956.229427-1-stephen.s.brennan@oracle.com> <20240502110348.016f190e0b0565b7e9ecdb48@kernel.org> <87r0e2pvmn.fsf@oracle.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@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 Wed, 15 May 2024 15:18:08 -0700 Stephen Brennan wrote: > Masami Hiramatsu (Google) writes: > > 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 Masami! > > I did want to check, is this the correct git tree to be watching? > > https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git/log/?h=probes/for-next > > ( I'm not trying to pressure on timing, as I know the merge window is > hectic. Just making sure I'm watching the correct place! ) Sorry, I forgot to push it from my local tree. Now it should be there. Thanks, -- Masami Hiramatsu (Google)