From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f182.google.com (mail-pf1-f182.google.com [209.85.210.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 36E8F32E73E for ; Wed, 17 Sep 2025 14:56:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758120983; cv=none; b=G559asFI6JPI0+M3+Nvkin4ci44W7L/Ee5XNPwfcQUJlO0lQTfqbHFejVIlyvjTh2wKCuR89uqZ1Ye/NGWNcb+8uRPqVcapsWMafi8sLKsKGDMOi4dLHGTnchTa6ngDiKxLfYVv36NELjaLeImUhdjm7OPpEMsie8xepBxoGcZY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758120983; c=relaxed/simple; bh=gicOMBaesdNTccvEzddk/YN/oDXQeNuzFolMvo4isZ4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=BYX5Cf+GNFN57TGlfn4xT9SyyGvHbUk3GGRyppGFeCumLAjYPsdhSweWAZnOcXkhD+p/lkb9WtraoAkKjp0uqZ4kwEROS86OKq/5ZjiwNH2eGrAQYMDLjL0PxnFvZ6qrGg8FNxdgxuL/2WfxY36yJlNZjKOTGqzejZpENVVpV7E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=furiosa.ai; spf=none smtp.mailfrom=furiosa.ai; dkim=pass (1024-bit key) header.d=furiosa.ai header.i=@furiosa.ai header.b=oiCeZZ6P; arc=none smtp.client-ip=209.85.210.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=furiosa.ai Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=furiosa.ai Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=furiosa.ai header.i=@furiosa.ai header.b="oiCeZZ6P" Received: by mail-pf1-f182.google.com with SMTP id d2e1a72fcca58-7762021c574so4334079b3a.0 for ; Wed, 17 Sep 2025 07:56:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=furiosa.ai; s=google; t=1758120980; x=1758725780; darn=vger.kernel.org; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=vGgjTNK+wdbeCWY6KMOb7s+5s0orqzod2SL7Bz5GX80=; b=oiCeZZ6P3v1RY/DC/aT0/k64vHpcg+rmZ2WEzpger9u5LevHFgP87BPM/qEoqLJRCZ RwPcvSWibYB9QJNIatvtrgO9JvgBpXrWlFGTws9S3N5pzMAjS6gvohm6UCK1ckqAhrCT 5oO6h2E793pbV82qF/AaVpIjwRJ2wf8qtP1O4= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758120980; x=1758725780; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=vGgjTNK+wdbeCWY6KMOb7s+5s0orqzod2SL7Bz5GX80=; b=V7OLV6fYXxmhIrGfZRrjBAW0Ofao//nzkr1AIow2HuaGxhwjVaIP9uRhfB3eztSoA2 ZlKpSpaSwJxKuT88WOF5LkY4fT60yQFemyw07fFb5TX1JQStbqxxaBLp9w9GVWTpHRYs phtltBQGH3xX1gDmDrHqyzmqEHlP4+roD6jslvm7CbteUKZcwjG0A/ZKe86QQjFmZGsK EUiKYrmK6MfyDi37/uXJzLOpf9iq1c3EFWHjDAUEWGqfrl03lJnR3K/BNsyV8xSDaev5 ygsDlu5R3AG32pjqhgaM1eRonHM7xmfKQIo7myZVUy5xD1D9Lw8rUCnVwNP969x7OS/l BY8Q== X-Forwarded-Encrypted: i=1; AJvYcCW/AC1L1kkN79m6XjDNrw5wMJWpbioBowNYRRjjqe8dc5e5d7ICDcZXqiipD4K0vX36lzPGoB/19A==@vger.kernel.org X-Gm-Message-State: AOJu0YxhZEM9SsdeY5xO9oFmbaOptlIaxCUMLayU5ONGb1GOqcQC0jig o/vWeKD4oKxO7pirgu7BRY+FxUbndRC0g87JSC62DOXQXSu22byJLFlnGKP+MnErETA= X-Gm-Gg: ASbGnctCU+uT5wrIGQXagnBjFcH1ZnCvAEcE63NQeZDHHsJTVy5rAndEQUNdNYbxqhz lhqKe1eDHZt/8Qo1OU0zsChsYLsa4brn/HtdJEWH1hZdhRxBA0gGP3ris1Qxvejgs6jYyFF9upx ak5BiPzflvCyArx2u6+LJNo+QGhHYOcB1F8ByR7kFpCAFB/KOMG1Xaw5AG18qLuPYZRNGPFbtk2 TV1p4H1Ho7RZI0kOZjtxVnNiPBKyqOBmp12CXiLQzX1gFI5gKpLDdtIiI6CJovAImUJ3l5U0tOL Mz3EnQZ9NcyTUhkj6ejuIF9K/PztuIbXjbIxfF1J5pQfiEFSQFJH0FCqtzifTYJr2k4ujFKNFho cI8zmVykDGssWtQuEA+0XjKNbQLwFuUUN6vWH70M4shX7MmaXJZxca1Chy/le3HZjVPo= X-Google-Smtp-Source: AGHT+IF38AXPY34Cdzv56BftkQZDZ9qSIcFh807nJJKWx6fVTWK3/9fTFBZvhx6xdeQWZibqjDWecQ== X-Received: by 2002:a05:6a00:986:b0:771:e4b0:4641 with SMTP id d2e1a72fcca58-77bf6dcfe59mr2978340b3a.1.1758120979976; Wed, 17 Sep 2025 07:56:19 -0700 (PDT) Received: from sidongui-MacBookPro.local ([175.195.128.78]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-77607c49fe4sm19473921b3a.101.2025.09.17.07.56.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Sep 2025 07:56:18 -0700 (PDT) Date: Wed, 17 Sep 2025 23:56:13 +0900 From: Sidong Yang To: Caleb Sander Mateos Cc: Jens Axboe , Daniel Almeida , Benno Lossin , Miguel Ojeda , Arnd Bergmann , Greg Kroah-Hartman , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, io-uring@vger.kernel.org Subject: Re: [RFC PATCH v3 2/5] io_uring/cmd: zero-init pdu in io_uring_cmd_prep() to avoid UB Message-ID: References: Precedence: bulk X-Mailing-List: io-uring@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: On Mon, Sep 15, 2025 at 09:54:50AM -0700, Caleb Sander Mateos wrote: > On Sat, Sep 13, 2025 at 5:42 AM Sidong Yang wrote: > > > > On Fri, Sep 12, 2025 at 10:56:31AM -0700, Caleb Sander Mateos wrote: > > > On Fri, Sep 12, 2025 at 9:42 AM Sidong Yang wrote: > > > > > > > > On Tue, Sep 09, 2025 at 09:32:37AM -0700, Caleb Sander Mateos wrote: > > > > > On Tue, Sep 9, 2025 at 7:43 AM Sidong Yang wrote: > > > > > > > > > > > > On Mon, Sep 08, 2025 at 12:45:58PM -0700, Caleb Sander Mateos wrote: > > > > > > > On Sat, Sep 6, 2025 at 7:28 AM Sidong Yang wrote: > > > > > > > > > > > > > > > > On Tue, Sep 02, 2025 at 08:31:00AM -0700, Caleb Sander Mateos wrote: > > > > > > > > > On Tue, Sep 2, 2025 at 3:23 AM Sidong Yang wrote: > > > > > > > > > > > > > > > > > > > > On Mon, Sep 01, 2025 at 05:34:28PM -0700, Caleb Sander Mateos wrote: > > > > > > > > > > > On Fri, Aug 22, 2025 at 5:56 AM Sidong Yang wrote: > > > > > > > > > > > > > > > > > > > > > > > > The pdu field in io_uring_cmd may contain stale data when a request > > > > > > > > > > > > object is recycled from the slab cache. Accessing uninitialized or > > > > > > > > > > > > garbage memory can lead to undefined behavior in users of the pdu. > > > > > > > > > > > > > > > > > > > > > > > > Ensure the pdu buffer is cleared during io_uring_cmd_prep() so that > > > > > > > > > > > > each command starts from a well-defined state. This avoids exposing > > > > > > > > > > > > uninitialized memory and prevents potential misinterpretation of data > > > > > > > > > > > > from previous requests. > > > > > > > > > > > > > > > > > > > > > > > > No functional change is intended other than guaranteeing that pdu is > > > > > > > > > > > > always zero-initialized before use. > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Sidong Yang > > > > > > > > > > > > --- > > > > > > > > > > > > io_uring/uring_cmd.c | 1 + > > > > > > > > > > > > 1 file changed, 1 insertion(+) > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c > > > > > > > > > > > > index 053bac89b6c0..2492525d4e43 100644 > > > > > > > > > > > > --- a/io_uring/uring_cmd.c > > > > > > > > > > > > +++ b/io_uring/uring_cmd.c > > > > > > > > > > > > @@ -203,6 +203,7 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) > > > > > > > > > > > > if (!ac) > > > > > > > > > > > > return -ENOMEM; > > > > > > > > > > > > ioucmd->sqe = sqe; > > > > > > > > > > > > + memset(&ioucmd->pdu, 0, sizeof(ioucmd->pdu)); > > > > > > > > > > > > > > > > > > > > > > Adding this overhead to every existing uring_cmd() implementation is > > > > > > > > > > > unfortunate. Could we instead track the initialized/uninitialized > > > > > > > > > > > state by using different types on the Rust side? The io_uring_cmd > > > > > > > > > > > could start as an IoUringCmd, where the PDU field is MaybeUninit, > > > > > > > > > > > write_pdu() could return a new IoUringCmdPdu that guarantees the > > > > > > > > > > > PDU has been initialized. > > > > > > > > > > > > > > > > > > > > I've found a flag IORING_URING_CMD_REISSUE that we could initialize > > > > > > > > > > the pdu. In uring_cmd callback, we can fill zero when it's not reissued. > > > > > > > > > > But I don't know that we could call T::default() in miscdevice. If we > > > > > > > > > > make IoUringCmdPdu, MiscDevice also should be MiscDevice. > > > > > > > > > > > > > > > > > > > > How about assign a byte in pdu for checking initialized? In uring_cmd(), > > > > > > > > > > We could set a byte flag that it's not initialized. And we could return > > > > > > > > > > error that it's not initialized in read_pdu(). > > > > > > > > > > > > > > > > > > Could we do the zero-initialization (or T::default()) in > > > > > > > > > MiscdeviceVTable::uring_cmd() if the IORING_URING_CMD_REISSUE flag > > > > > > > > > isn't set (i.e. on the initial issue)? That way, we avoid any > > > > > > > > > performance penalty for the existing C uring_cmd() implementations. > > > > > > > > > I'm not quite sure what you mean by "assign a byte in pdu for checking > > > > > > > > > initialized". > > > > > > > > > > > > > > > > Sure, we could fill zero when it's the first time uring_cmd called with > > > > > > > > checking the flag. I would remove this commit for next version. I also > > > > > > > > suggests that we would provide the method that read_pdu() and write_pdu(). > > > > > > > > In read_pdu() I want to check write_pdu() is called before. So along the > > > > > > > > 20 bytes for pdu, maybe we could use a bytes for the flag that pdu is > > > > > > > > initialized? > > > > > > > > > > > > > > Not sure what you mean about "20 bytes for pdu". > > > > > > > It seems like it would be preferable to enforce that write_pdu() has > > > > > > > been called before read_pdu() using the Rust type system instead of a > > > > > > > runtime check. I was thinking a signature like fn write_pdu(cmd: > > > > > > > IoUringCmd, value: T) -> IoUringCmdPdu. Do you feel there's a > > > > > > > reason that wouldn't work and a runtime check would be necessary? > > > > > > > > > > > > I didn't think about make write_pdu() to return IoUringCmdPdu before. > > > > > > I think it's good way to pdu is safe without adding a new generic param for > > > > > > MiscDevice. write_pdu() would return IoUringCmdPdu and it could call > > > > > > IoUringCmdPdu::pdu(&mut self) -> &mut T safely maybe. > > > > > > > > > > Yes, that's what I was thinking. > > > > > > > > Good, I'll change api in this way. Thanks! > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > But maybe I would introduce a new struct that has Pin<&mut IoUringCmd> and > > > > > > > > issue_flags. How about some additional field for pdu is initialized like below? > > > > > > > > > > > > > > > > struct IoUringCmdArgs { > > > > > > > > ioucmd: Pin<&mut IoUringCmd>, > > > > > > > > issue_flags: u32, > > > > > > > > pdu_initialized: bool, > > > > > > > > } > > > > > > > > > > > > > > One other thing I realized is that issue_flags should come from the > > > > > > > *current* context rather than the context the uring_cmd() callback was > > > > > > > called in. For example, if io_uring_cmd_done() is called from task > > > > > > > work context, issue_flags should match the issue_flags passed to the > > > > > > > io_uring_cmd_tw_t callback, not the issue_flags originally passed to > > > > > > > the uring_cmd() callback. So it probably makes more sense to decouple > > > > > > > issue_flags from the (owned) IoUringCmd. I think you could pass it by > > > > > > > reference (&IssueFlags) or with a phantom reference lifetime > > > > > > > (IssueFlags<'_>) to the Rust uring_cmd() and task work callbacks to > > > > > > > ensure it can't be used after those callbacks have returned. > > > > > > > > > > > > I have had no idea about task work context. I agree with you that > > > > > > it would be better to separate issue_flags from IoUringCmd. So, > > > > > > IoUringCmdArgs would have a only field Pin<&mut IoUringCmd>? > > > > > > > > > > "Task work" is a mechanism io_uring uses to queue work to run on the > > > > > thread that submitted an io_uring operation. It's basically a > > > > > per-thread atomic queue of callbacks that the thread will process > > > > > whenever it returns from the kernel to userspace (after a syscall or > > > > > an interrupt). This is the context where asynchronous uring_cmd > > > > > completions are generally processed (see > > > > > io_uring_cmd_complete_in_task() and io_uring_cmd_do_in_task_lazy()). I > > > > > can't speak to the history of why io_uring uses task work, but my > > > > > guess would be that it provides a safe context to acquire the > > > > > io_ring_ctx uring_lock mutex (e.g. nvme_uring_cmd_end_io() can be > > > > > called from an interrupt handler, so it's not allowed to take a > > > > > mutex). Processing all the task work at once also provides natural > > > > > opportunities for batching. > > > > > > > > Thanks, I've checked io_uring_cmd_complete_in_task() that it receives > > > > callback that has issue_flags different with io_uring_cmd(). I'll try to add > > > > a api that wrapping io_uring_cmd_complete_in_task() for next version. > > > > > > > > > > > > > > Yes, we probably don't need to bundle anything else with the > > > > > IoUringCmd after all. As I mentioned earlier, I don't think Pin<&mut > > > > > IoUringCmd> will work for uring_cmds that complete asynchronously, as > > > > > they will need to outlive the uring_cmd() call. So uring_cmd() needs > > > > > to transfer ownership of the struct io_uring_cmd. > > > > > > > > I can't think that how to take ownership of struct io_uring_cmd. The > > > > struct allocated with io_alloc_req() and should be freed with io_free_req(). > > > > If taking ownership means having pointer of struct io_uring_cmd, I think > > > > it's no difference with current version. Also could it be called with > > > > mem::forget() if it has ownership? > > > > > > I don't mean ownership of the io_uring_cmd allocation; that's the > > > responsibility of the io_uring layer. But once the io_uring_cmd is > > > handed to the uring_cmd() implementation, it belongs to that layer > > > until it completes the command back to io_uring. Maybe a better way to > > > describe it would be as ownership of the "executing io_uring_cmd". The > > > problem with Pin<&mut IoUringCmd> is that it is a borrowed reference > > > to the io_uring_cmd, so it can't outlive the uring_cmd() callback. > > > Yes, it's possible to leak the io_uring_cmd by never calling > > > io_uring_cmd_done() to return it to the io_uring layer. > > > > Thanks, I understood that IoUringCmd could be outlive uring_cmd callback. > > But it's sad that it could be leaked without any unsafe code. > > Safety in Rust doesn't require destructors to run, which means any > resource can be safely leaked > (https://faultlore.com/blah/everyone-poops/ has some historical > background on why Rust decided leaks had to be considered safe). > Leaking an io_uring_cmd is analogous to leaking a Box, both are > perfectly possible in safe Rust. Thanks for the reference. If driver just drops `IoUringCmd` without taking, the request wouldn't be completed until io-uring instance deinitialized. I understood that we cannot handle this. > > > > > > > > > I would imagine something like this: > > > > > > #[derive(Clone, Copy)] > > > struct IssueFlags<'a>(c_uint, PhantomData<&'a ()>); > > > > > > // Indicates ownership of the io_uring_cmd between uring_cmd() and > > > io_uring_cmd_done() > > > struct IoUringCmd(NonNull); > > > > > > impl IoUringCmd { > > > // ... > > > > > > fn done(self, ret: i32, res2: u64, issue_flags: IssueFlags<'_>) { > > > let cmd = self.0.as_ptr(); > > > let issue_flags = issue_flags.0; > > > unsafe { > > > bindings::io_uring_cmd_done(cmd, ret, res2, issue_flags) > > > } > > > } > > > } > > > > > > // Can choose whether to complete the command synchronously or asynchronously. > > > // If take_async() is called, IoUringCmd::done() needs to be called to > > > complete the command. > > > // If take_async() isn't called, the command is completed synchronously > > > // with the return value from MiscDevice::uring_cmd(). > > > struct UringCmdInput<'a>(&mut Option>); > > > > Thanks for a detailed example! > > > > But rather than this, We could introduce new return type that has a callback that > > user could take IoUringCmd instead of returning -EIOCBQUEUED. > > I'm not following what you're suggesting, maybe a code sample would help? maybe like below... #[vtable] pub trait MiscDevice: Sized { /// ... /// If user returns `EIOCBQUEUED`, this function would be called for /// users who want to take `IoUringCmdAsync`. It could call `done()` for complete /// request. fn uring_cmd_async_prep( device: ::Borrowed<'_>, io_uring_cmd_async: IoUringCmdAsync); /// ... } impl MiscdeviceVTable { // ... unsafe extern "C" fn uring_cmd( ioucmd: *mut bindings::io_uring_cmd, issue_flags: ffi::c_uint, ) -> c_int { // ... let result = T::uring_cmd(device, ioucmd, issue_flags); if let Err(EIOCBQUEUED) = result { T::uring_cmd_async_prep(device, ioucmd.to_async()); } from_result(|| result) } } > > > > > But I prefer that we provide just one type IoUringCmd without UringCmdInput. > > Although UringCmdInput, user could call done() in uring_cmd callback and > > it makes confusion that whether task_async() called and returning -EIOCBQUEUED > > is mismatched that returns -EINVAL. We don't need to make it complex. > > Sure, if you only want to support asynchronous io_uring_cmd > completions, than you can just pass IoUringCmd to > MiscDevice::uring_cmd() and require it to call IoUringCmd::done() to > complete the command. There's a small performance overhead to that > over just returning the result from the uring_cmd() callback for > synchronous completions (and it's more verbose), but I think that > would be fine for an initial implementation. I appreciate for your understanding. I think it would be good to have just one simple struct `IoUringCmd`. I'll make next version patch soon. Thanks, Sidong > > Best, > Caleb