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 47FA117A309 for ; Fri, 19 Jun 2026 16:05:50 +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=1781885151; cv=none; b=nr7IwD8hKLrEXgmwodK3TJFEvWZCbiV34H59U4jo6VQz8nSZdGYhWly4xb1BrWKmgR9H5hJftusBmTulq/eGTvNYjEX8XeTiTodWcHKMWKH6/M4++1Bo5wurMI7gGn6araMwpOB8c2TqQjc1wavIUH3nkm1L4hn8nq8a3Nojch8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781885151; c=relaxed/simple; bh=od/LVkeOBi4HrtvP8P/BfE3NmXUuPDGUB4eYeMLwtoM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PkEFlIDhgXrjbwOZnUANo0oW5DhNAwhD8eHh7KecSSiPC89c0F0OD2tgywcOygpAA2kSVoFEA0HJbIJfesDwRRczO5+aSq1SoMtTdj5ZE6YvAoosjeAYy8RD0XgLN4f2MssCPcvtwOhCbmTV9ll8eo/VPkhujSl19ieZZELgB30= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A0big/Lp; 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="A0big/Lp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E30E21F000E9; Fri, 19 Jun 2026 16:05:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781885149; bh=X2shzPwH02GzeAm1HaM4r3qbFbXKwpyKGG4nj4wIXZo=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=A0big/Lpttf9pHiCucSIylvS6ZzrhQPLaePLgIjbLA7VPHL+sJTBUo8JZzMxS+hNx evhJMwziwnBLkz7zxiEDsvyCM+oYHTzqp8X9WNC4tJvn4a+z0JnZot0qa3g4eN/sAp XFeFKAVGu/Rxz7+3s8Q4Je3NCh9ebooF//2npFS6FTWHU3slPw28+Y57kEjh5p4bvE rLyLZKYnVD+j86aABxFsPukUJK/0/prbn99WW3i56XzFmFNEFaFd2ppBf0tF7KDoYY 5HZdO7TJXtqVl/FwF1vQD7ADcVcOPFO8H1NkZ/Ya/APu5wkUOlLVlKUYD9Zf2I2oZa vgyMSJlWUhvIw== Date: Fri, 19 Jun 2026 17:05:44 +0100 From: Will Deacon To: Yiqi Sun Cc: catalin.marinas@arm.com, kees@kernel.org, keno@juliacomputing.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, luis.machado@linaro.org, mark.rutland@arm.com, rmk+kernel@armlinux.org.uk, ruanjinjie@huawei.com Subject: Re: Re: [PATCH] fix: arm64: syscall: use live x0 for syscall_get_arguments() arg0 Message-ID: References: <20260603090730.16960-1-sunyiqixm@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260603090730.16960-1-sunyiqixm@gmail.com> On Wed, Jun 03, 2026 at 05:07:30PM +0800, Yiqi Sun wrote: > On Mon, 1 Jun 2026 13:43:42 +0100, Well wrote: > > On Fri, May 29, 2026 at 02:54:44PM +0800, Yiqi Sun wrote: > > > On arm64, seccomp obtains syscall arguments via syscall_get_arguments(), > > > where arg0 is currently read from regs->orig_x0. However, the syscall > > > wrapper consumes live arguments from regs->regs[0..5]. > > > > > > A ptracer can modify x0 on syscall-enter stop before seccomp runs, > > > but cannot update orig_x0 through that interface. This can > > > leave seccomp checking stale arg0 while the syscall executes with updated > > > live x0, allowing seccomp bypass when filters depend on arg0. > > > > > > Make syscall_get_arguments() read arg0 from regs->regs[0], matching the > > > actual dispatch arguments and removing this desynchronization. > > > > > > Fixes: f27bb139c387 ("arm64: Miscellaneous library functions") > > > Signed-off-by: Yiqi Sun > > > --- > > > arch/arm64/include/asm/syscall.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h > > > index 5e4c7fc44f73..4bdb4d3ce2b4 100644 > > > --- a/arch/arm64/include/asm/syscall.h > > > +++ b/arch/arm64/include/asm/syscall.h > > > @@ -81,7 +81,7 @@ static inline void syscall_get_arguments(struct task_struct *task, > > > struct pt_regs *regs, > > > unsigned long *args) > > > { > > > - args[0] = regs->orig_x0; > > > + args[0] = regs->regs[0]; > > > args[1] = regs->regs[1]; > > > args[2] = regs->regs[2]; > > > args[3] = regs->regs[3]; > > > -- > > > 2.34.1 > > > > Hrm, this looks like a long-standing issue and I'm pretty nervous about > > changing it :/ > > > > How did you spot it? > > I share your concern here, and I’m trying to be very careful with any > behavior change. > > I spotted this while comparing seccomp+ptrace ordering across arches. > I had previously looked at x86/x86_64 (including the seccomp/ptrace > ordering fix from more than 10 years ago), and then checked whether > other arches like arm64 had the same issue. > > > A quick look at the code suggests we have a similar issue with > > audit_syscall_entry(), so if we take your patch here then it will silently > > introduce a behavioural change to this guy: > > > > https://lore.kernel.org/all/20260320102620.1336796-5-ruanjinjie@huawei.com/ > > > > I also notice that the compat ptrace interface allows 'orig_x0' to be > > set -- could that cause issues with things like syscall_rollback()? > > Will > > You are right that on arm64, audit_syscall_entry() still takes arg0 > from orig_x0, so taking only this seccomp fix would diverge seccomp > and audit semantics. > > I also checked syscall_rollback(): on arm64 it restores regs[0] from > orig_x0, and orig_x0 is captured at syscall entry before the ptrace > syscall-stop hook. So rollback normally returns to the syscall-entry > state (i.e. pre-ptrace argument value), which does not look like a new > security issue by itself. compat ptrace can explicitly write orig_x0, > but that is existing tracer-controlled behavior and does not, by itself, > cross a new security boundary introduced by this patch. > > If you agree, I can send a follow-up later so seccomp/audit stay consistent. Yes, please send a v2 that fixes audit at the same time. Will