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 99CC8C25B77 for ; Thu, 16 May 2024 00:24:55 +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=eyhYvQrh; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4VfrT15QtHz3dVj for ; Thu, 16 May 2024 10:24:53 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=kernel.org 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=eyhYvQrh; 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 4VfrS95tKVz3cjm for ; Thu, 16 May 2024 10:24:09 +1000 (AEST) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sin.source.kernel.org (Postfix) with ESMTP id 8264ECE17F6; Thu, 16 May 2024 00:24:06 +0000 (UTC) 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 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) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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" 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)