From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from vmicros1.altlinux.org (vmicros1.altlinux.org [194.107.17.57]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 5B00A24A7F6; Thu, 16 Jan 2025 16:04:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.107.17.57 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737043453; cv=none; b=LZR5GibwXrdiJyZWPi7DNZotGmKBNyuH1lDJnBYoRwNclM7E/I2uzUVtmfD00qoW+BPDLtQBQfUE1SLvrl+MUgbJrT59gesTCBN2sZt6sbw4QMnYV0HtYFJNvv4+3n6ega7kgprxuvrps5vUmb+BdzzNb9s3LJbGIBHXOrmPmN8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737043453; c=relaxed/simple; bh=X/N4/BXrk+bh43rgRGbrNL95bTuJNZzRxIK97gdDp1E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=bmZhoVZmiNlRcSwxLXo41lmXinghpAae+9zyI2DRYSYhJunrDrbozbu+Rr99Gl7+4nJjBW0A0WF4YAwrXrI6cNy93EE6ZLhm7XM6HyDR4t84o5v0yQfH79RcpAwqgGvZN7M7PvdLVIqJr8QMPsvPCBq1Ll9OH8rHewBk2IinjYc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strace.io; spf=pass smtp.mailfrom=altlinux.org; arc=none smtp.client-ip=194.107.17.57 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strace.io Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=altlinux.org Received: from mua.local.altlinux.org (mua.local.altlinux.org [192.168.1.14]) by vmicros1.altlinux.org (Postfix) with ESMTP id 5967372C8CC; Thu, 16 Jan 2025 19:04:03 +0300 (MSK) Received: by mua.local.altlinux.org (Postfix, from userid 508) id 4E2EC7CCB3A; Thu, 16 Jan 2025 18:04:03 +0200 (IST) Date: Thu, 16 Jan 2025 18:04:03 +0200 From: "Dmitry V. Levin" To: Oleg Nesterov Cc: Eugene Syromyatnikov , Mike Frysinger , Renzo Davoli , Davide Berardi , strace-devel@lists.strace.io, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [PATCH v2 6/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO request Message-ID: <20250116160403.GA3554@strace.io> References: <20250113170925.GA392@strace.io> <20250113171208.GF589@strace.io> <20250116152137.GE21801@redhat.com> Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250116152137.GE21801@redhat.com> On Thu, Jan 16, 2025 at 04:21:38PM +0100, Oleg Nesterov wrote: > On 01/13, Dmitry V. Levin wrote: > > > > +static int > > +ptrace_set_syscall_info(struct task_struct *child, unsigned long user_size, > > + void __user *datavp) > > +{ > > + struct pt_regs *regs = task_pt_regs(child); > > + struct ptrace_syscall_info info; > > + int error; > > + > > + BUILD_BUG_ON(sizeof(struct ptrace_syscall_info) < PTRACE_SYSCALL_INFO_SIZE_VER0); > > + > > + if (user_size < PTRACE_SYSCALL_INFO_SIZE_VER0 || user_size > PAGE_SIZE) > > + return -EINVAL; > > + > > + error = copy_struct_from_user(&info, sizeof(info), datavp, user_size); > > OK, I certainly can't understand why copy_struct_from_user/check_zeroed_user > is useful, at least in this case. In particular, this won't allow to run the > new code (which uses the "extended" ptrace_syscall_info) on the older kernels? > > Can't we just use user_size as a version number? > > We can also turn info->reserved into info->version filled by > ptrace_get_syscall_info(). > > ptrace_set_syscall_info() can check that info->version matches user_size. The idea is to use "op" to specify the operation, and "flags" to specify future extensions to the operation. For example, we could later add PTRACE_SYSCALL_INFO_SECCOMP_SKIP operation to specify an exit-like data for seccomp stops, or some flag to set instruction_pointer or stack_pointer. I don't think any of these would require a version field, though. That is, the zero check implied by copy_struct_from_user() is not really needed here since the compatibility is tracked by "op" and "flags": if "op" and "flags" do not instruct the kernel to use these unknown extra bits, the kernel is not obliged to check them either. For the same reason I don't think the kernel is obliged to read more than sizeof(info) from userspace. What would you recommend using instead of copy_struct_from_user in this case? -- ldv