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[79.43.130.89]) by smtp.gmail.com with ESMTPSA id 133sm8550375wme.9.2019.01.07.13.19.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 07 Jan 2019 13:19:05 -0800 (PST) Date: Mon, 7 Jan 2019 22:19:04 +0100 From: Andrea Righi To: Steven Rostedt Cc: Masami Hiramatsu , Ingo Molnar , peterz@infradead.org, Mathieu Desnoyers , linux-kernel Subject: Re: [PATCH 0/2] kprobes: Fix kretprobe incorrect stacking order problem Message-ID: <20190107211904.GC5966@xps-13> References: <154686789378.15479.2886543882215785247.stgit@devbox> <20190107183444.GA5966@xps-13> <20190107142749.34231bb6@gandalf.local.home> <20190107195209.GB5966@xps-13> <20190107145918.407b851b@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190107145918.407b851b@gandalf.local.home> 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 Mon, Jan 07, 2019 at 02:59:18PM -0500, Steven Rostedt wrote: > On Mon, 7 Jan 2019 20:52:09 +0100 > Andrea Righi wrote: > > > > Ug, kretprobe calls spinlocks in the callback? I wonder if we can > > > remove them. > > > > > > I'm guessing this is a different issue than the one that this patch > > > fixes. This sounds like we are calling kretprobe from kretprobe? > > > > > > -- Steve > > > > kretprobe_trampoline() > > -> trampoline_handler() > > -> kretprobe_hash_lock() > > -> raw_spin_lock_irqsave() > > > > If we put a kretprobe to raw_spin_lock_irqsave() it looks like > > kretprobe is going to call kretprobe... > > Right, but we should be able to add some recursion protection to stop > that. I have similar protection in the ftrace code. If we assume that __raw_spin_lock/unlock*() are always inlined a possible way to prevent this recursion could be to use directly those functions to do locking from the kretprobe trampoline. But I'm not sure if that's a safe assumption... if not I'll see if I can find a better solution. Thanks, From: Andrea Righi Subject: [PATCH] kprobes: prevent recursion deadlock with kretprobe and spinlocks kretprobe_trampoline() is using a spinlock to protect the hash of kretprobes. Adding a kretprobe to the spinlock functions may cause a recursion deadlock where kretprobe is calling itself: kretprobe_trampoline() -> trampoline_handler() -> kretprobe_hash_lock() -> raw_spin_lock_irqsave() -> _raw_spin_lock_irqsave() kretprobe_trampoline from _raw_spin_lock_irqsave => DEADLOCK kretprobe_trampoline() -> trampoline_handler() -> recycle_rp_inst() -> raw_spin_lock() -> _raw_spin_lock() kretprobe_trampoline from _raw_spin_lock => DEADLOCK Use the corresponding inlined spinlock functions to prevent this recursion. Signed-off-by: Andrea Righi --- kernel/kprobes.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/kprobes.c b/kernel/kprobes.c index f4ddfdd2d07e..b89bef5e3d80 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -1154,9 +1154,9 @@ void recycle_rp_inst(struct kretprobe_instance *ri, hlist_del(&ri->hlist); INIT_HLIST_NODE(&ri->hlist); if (likely(rp)) { - raw_spin_lock(&rp->lock); + __raw_spin_lock(&rp->lock); hlist_add_head(&ri->hlist, &rp->free_instances); - raw_spin_unlock(&rp->lock); + __raw_spin_unlock(&rp->lock); } else /* Unregistering */ hlist_add_head(&ri->hlist, head); @@ -1172,7 +1172,7 @@ __acquires(hlist_lock) *head = &kretprobe_inst_table[hash]; hlist_lock = kretprobe_table_lock_ptr(hash); - raw_spin_lock_irqsave(hlist_lock, *flags); + *flags = __raw_spin_lock_irqsave(hlist_lock); } NOKPROBE_SYMBOL(kretprobe_hash_lock); @@ -1193,7 +1193,7 @@ __releases(hlist_lock) raw_spinlock_t *hlist_lock; hlist_lock = kretprobe_table_lock_ptr(hash); - raw_spin_unlock_irqrestore(hlist_lock, *flags); + __raw_spin_unlock_irqrestore(hlist_lock, *flags); } NOKPROBE_SYMBOL(kretprobe_hash_unlock); -- 2.17.1