From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 D026938DC5D; Thu, 30 Jul 2026 03:36:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785382597; cv=none; b=WmsdEVxEUuplokF+hmYt/OexIyHmi0ryFqEhVH3PHHJwbIXYzREiX0QlQxh4gwFbSeHfQTTIgiLzWikJAvuzH3y0Tkwy/q/brlnhAeo5d1RfR6viMRF5H7HpF2WpnWLaJhFjdzFdM2Bd2BV3omf8LSYs2PEDlHG1k6FwMgnvOQo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785382597; c=relaxed/simple; bh=Brq2O2NUj020BWdizA1Qra/clwlZgf9+GiHIfOtO7AQ=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=RuUNxQMxqA8Brtuhr82qexLhx6NLlsm7ZLxjCPXHROW7V0fPmyXVlxvvxqeKUZgy4zU2FP6cjzq/tP7RrpXaPak1fklAMRIxvv/pKhPj2N2kX40aTpZYN10bR08ykdWtsrtT/4ycBHHXWFCVQIHIXyyIz+uottBCJSEpNntTIkE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ABD13DBr; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ABD13DBr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5690F1F000E9; Thu, 30 Jul 2026 03:36:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785382594; bh=/F8NTVlBDU8BWWwofVpJEhV+ebxXNRLNpFOKVh13JaY=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=ABD13DBr4Q7DY/MQkAi0/YOOzVJHdAj0jV8UgPzWpT1UDMDSquLjCjXpDKwVWExLf HA1vK5VSZse2IQ6xRMxCqptH//NixFj4t+xQHuGUG8avNB+Z2hvI5ksvvB4qXWF0+g xFlJvgwuxolComBVDBzZI2LrwjJ3In8uRmshmelBaOjANk3xiSAW4Xb8wO0QEM/4BA qlI3IXeAxHJjyM7HwvEpcqJejooXZ7rxHxAdBGpInilZf9wk07gd8tbPfG39hBtXcX szv+xzZz3OV0XOkqJf6RhpfQFNinm8/qVWBtx8HHL2jM5AzQXBxGe11xYl6ILJOHhA grv5+sVrBGtYw== Date: Thu, 30 Jul 2026 12:36:30 +0900 From: Masami Hiramatsu (Google) To: sashiko-reviews@lists.linux.dev Cc: sashiko-bot@kernel.org, linux-perf-users@vger.kernel.org Subject: Re: [PATCH] uprobes: Remove redundant guard(rcu) in find_active_uprobe_speculative() Message-Id: <20260730123630.5cdccc5334a0d9fa04a54f34@kernel.org> In-Reply-To: <20260730015947.ECA9A1F000E9@smtp.kernel.org> References: <178537593930.153254.1296986092000402239.stgit@devnote2> <20260730015947.ECA9A1F000E9@smtp.kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-perf-users@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 Thu, 30 Jul 2026 01:59:47 +0000 sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [High] Removing `guard(rcu)()` from `find_active_uprobe_speculative()` eliminates standard RCU protection, exposing lockless VMA and file accesses to Use-After-Free and page faults. > -- > > --- Patch [1]: [PATCH] uprobes: Remove redundant guard(rcu) in find_active_uprobe_speculative() --- > commit 008639a39e6344f6f057b7d120c62792b7cd6ddf > Author: Masami Hiramatsu (Google) > > uprobes: Remove redundant guard(rcu) in find_active_uprobe_speculative() > > This commit removes the guard(rcu)() from find_active_uprobe_speculative() > and adds a lockdep assertion for RCU Tasks Trace, assuming Tasks Trace RCU > protection provided by the caller is sufficient. > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > > index 07f69dd3093d5..52833db53b25c 100644 > > --- a/kernel/events/uprobes.c > > +++ b/kernel/events/uprobes.c > > @@ -2416,6 +2416,7 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) > > return is_trap_insn(&opcode); > > } > > > > +/* assumes being inside RCU Tasks Trace protected region */ > > static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr) > > { > > struct mm_struct *mm = current->mm; > > @@ -2425,7 +2426,7 @@ static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr) > > loff_t offset; > > unsigned int seq; > > > > - guard(rcu)(); > > + lockdep_assert(rcu_read_lock_trace_held()); > > > > if (!mmap_lock_speculate_try_begin(mm, &seq)) > > return NULL; > > [Severity: High] > Does removing the standard RCU protection here expose the subsequent VMA and > file accesses to use-after-free and page faults? > Oops, this guard() is for protecting VMA. OK, please ignore this. Thanks, > The VMA and file objects are allocated from SLAB_TYPESAFE_BY_RCU caches, > meaning their underlying slab pages can be returned to the page allocator > after a standard RCU grace period. RCU Tasks Trace does not block standard > RCU grace periods. > > The subsequent call to vma_lookup() briefly takes standard RCU to safely walk > the Maple Tree, but drops it before returning the VMA pointer. If the thread > is preempted after this point, and another thread unmaps the VMA and closes > the file, a standard RCU grace period could complete, freeing the VMA and file > slab pages. > > When the thread wakes up and dereferences vma->vm_file or vm_file->f_inode on > a freed page, could it cause a fatal page fault? The code relies on the VMA > and file not being freed from under it, which appears to require standard RCU > protection. > > -- > Sashiko AI review ยท https://sashiko.dev/#/patchset/178537593930.153254.1296986092000402239.stgit@devnote2?part=1 -- Masami Hiramatsu (Google)