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[79.43.130.89]) by smtp.gmail.com with ESMTPSA id k128sm12226301wmd.37.2019.01.08.02.31.02 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 08 Jan 2019 02:31:02 -0800 (PST) Date: Tue, 8 Jan 2019 11:31:01 +0100 From: Andrea Righi To: Masami Hiramatsu Cc: Ingo Molnar , peterz@infradead.org, Mathieu Desnoyers , linux-kernel , Steven Rostedt , stable@vger.kernel.org Subject: Re: [PATCH v2 0/3] kprobes: Fix kretprobe issues Message-ID: <20190108103101.GE5966@xps-13> References: <154692263564.1133.17363562046971295490.stgit@devbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <154692263564.1133.17363562046971295490.stgit@devbox> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 08, 2019 at 01:43:55PM +0900, Masami Hiramatsu wrote: > Hello, > > This is v2 series of fixing kretprobe incorrect stacking order patches. > In this version, I fixed a lack of kprobes.h including and added new > patch for kretprobe trampoline recursion issue. (and add Cc:stable) > > (1) kprobe incorrct stacking order problem > > On recent talk with Andrea, I started more precise investigation on > the kernel panic with kretprobes on notrace functions, which Francis > had been reported last year ( https://lkml.org/lkml/2017/7/14/466 ). > > See the investigation details in > https://lkml.kernel.org/r/154686789378.15479.2886543882215785247.stgit@devbox > > When we put a kretprobe on ftrace_ops_assist_func() and put another > kretprobe on probed-function, below happens > > > -> > ->fentry > ->ftrace_ops_assist_func() > ->int3 > ->kprobe_int3_handler() > ...->pre_handler_kretprobe() > push the return address (*fentry*) of ftrace_ops_assist_func() to > top of the kretprobe list and replace it with kretprobe_trampoline. > <-kprobe_int3_handler() > <-(int3) > ->kprobe_ftrace_handler() > ...->pre_handler_kretprobe() > push the return address (caller) of probed-function to top of the > kretprobe list and replace it with kretprobe_trampoline. > <-(kprobe_ftrace_handler()) > <-(ftrace_ops_assist_func()) > [kretprobe_trampoline] > ->tampoline_handler() > pop the return address (caller) from top of the kretprobe list > <-(trampoline_handler()) > > [run caller with incorrect stack information] > <-() > !!KERNEL PANIC!! > > Therefore, this kernel panic happens only when we put 2 k*ret*probes on > ftrace_ops_assist_func() and other functions. If we put kprobes, it > doesn't cause any issue, since it doesn't change the return address. > > To fix (or just avoid) this issue, we can introduce a frame pointer > verification to skip wrong order entries. And I also would like to > blacklist those functions because those are part of ftrace-based > kprobe handling routine. > > (2) kretprobe trampoline recursion problem > > This was found by Andrea in the previous thread > https://lkml.kernel.org/r/20190107183444.GA5966@xps-13 > > ---- > echo "r:event_1 __fdget" >> kprobe_events > echo "r:event_2 _raw_spin_lock_irqsave" >> kprobe_events > echo 1 > events/kprobes/enable > [DEADLOCK] > ---- > > Because kretprobe trampoline_handler uses spinlock for protecting > hash table, if we probe the spinlock itself, it causes deadlock. > Thank you Andrea and Steve for discovering this root cause!! > > This bug has been introduced with the asm-coded trampoline > code, since previously it used another kprobe for hooking > the function return placeholder (which only has a nop) and > trampoline handler was called from that kprobe. > > To fix this bug, I introduced a dummy kprobe and set it in > current_kprobe as we did in old days. > > Thank you, It looks all good to me, with this patch set I couldn't break the kernel in any way. Tested-by: Andrea Righi Thanks, -Andrea