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 8150F18C08; Wed, 1 May 2024 17:24:18 +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=1714584258; cv=none; b=eymU2cdFcUW6R7PQGAqIaapIvAu4JlA1QakKZXciA4VkDYkwqZUeOBpOXDfvC4NaEJems3lasXlLFdRvPZl+aTfbynTyoecuS2p3piS0GVMthR2/8Ti4MyqJh0jCSI4TnufdxwFOhseQBrIu4y7fHRkFzGpHSg5eZKlkVx1xze8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714584258; c=relaxed/simple; bh=l3KI1mpm3TLzcA+uIN1rJJ4uvAsCdYr6Lv0kEgC1Fmg=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=nlSQAI+PHahM+RKuB+SFuYxRvbO5soPogUOmPCsEbYCZxWGM36Bt71EoETadFDEdwzDmcS1Vaw6QMU1G19hVL7W7K7fkF4b+U2uziKBYrcuNaIgkD4CHmYjBQIyaKtuUbeNSDgqWm+aWnkjjPAQqC6KOT9rpThNSm5AFPs+s1ms= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 622E2C072AA; Wed, 1 May 2024 17:24:14 +0000 (UTC) Date: Wed, 1 May 2024 13:24:58 -0400 From: Steven Rostedt To: Stephen Brennan Cc: Masami Hiramatsu , Mark Rutland , Guo Ren , 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: <20240501132458.3ea28f6b@gandalf.local.home> In-Reply-To: <20240501162956.229427-1-stephen.s.brennan@oracle.com> References: <20240501162956.229427-1-stephen.s.brennan@oracle.com> X-Mailer: Claws Mail 3.19.1 (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=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 1 May 2024 09:29:56 -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. > > 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. Reviewed-by: Steven Rostedt (Google) Thanks, -- Steve