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auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200921_112140_340952_58056CFA X-CRM114-Status: GOOD ( 26.39 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , "linux-s390@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-parisc@vger.kernel.org" , Arnd Bergmann , "linux-aio@kvack.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , David Howells , "linux-fsdevel@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-mm@kvack.org" , "linux-scsi@vger.kernel.org" , "sparclinux@vger.kernel.org" , Andrew Morton , "linuxppc-dev@lists.ozlabs.org" , "io-uring@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Al Viro > Sent: 21 September 2020 16:02 > > On Mon, Sep 21, 2020 at 04:34:25PM +0200, Christoph Hellwig wrote: > > From: David Laight > > > > This is the only direct call of rw_copy_check_uvector(). Removing it > > will allow rw_copy_check_uvector() to be inlined into import_iovec(), > > while only paying a minor price by setting up an otherwise unused > > iov_iter in the process_vm_readv/process_vm_writev syscalls that aren't > > in a super hot path. > > > @@ -443,7 +443,7 @@ void iov_iter_init(struct iov_iter *i, unsigned int direction, > > const struct iovec *iov, unsigned long nr_segs, > > size_t count) > > { > > - WARN_ON(direction & ~(READ | WRITE)); > > + WARN_ON(direction & ~(READ | WRITE | CHECK_IOVEC_ONLY)); > > direction &= READ | WRITE; > > Ugh... > > > - rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV, > > - iovstack_r, &iov_r); > > + rc = import_iovec(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV, &iov_r, > > + &iter_r); > > if (rc <= 0) > > goto free_iovecs; > > > > - rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write); > > + rc = process_vm_rw_core(pid, &iter_l, iter_r.iov, iter_r.nr_segs, > > + flags, vm_write); > > ... and ugh^2, since now you are not only setting a meaningless iov_iter, > you are creating a new place that pokes directly into struct iov_iter > guts. > > Sure, moving rw_copy_check_uvector() over to lib/iov_iter.c makes sense. > But I would rather split the access_ok()-related checks out of that thing > and bury CHECK_IOVEC_ONLY. > > Step 1: move the damn thing to lib/iov_iter.c (same as you do, but without > making it static) > > Step 2: split it in two: > > ssize_t rw_copy_check_uvector(const struct iovec __user * uvector, > unsigned long nr_segs, unsigned long fast_segs, > struct iovec *fast_pointer, > struct iovec **ret_pointer) > { > unsigned long seg; ... > ret = 0; > for (seg = 0; seg < nr_segs; seg++) { > void __user *buf = iov[seg].iov_base; > ssize_t len = (ssize_t)iov[seg].iov_len; > > /* see if we we're about to use an invalid len or if > * it's about to overflow ssize_t */ > if (len < 0) > return -EINVAL; > if (len > MAX_RW_COUNT - ret) { > len = MAX_RW_COUNT - ret; > iov[seg].iov_len = len; > } > ret += len; > } > return ret; > } > > /* > * This is merely an early sanity check; we do _not_ rely upon > * it when we get to the actual memory accesses. > */ > static bool check_iovecs(const struct iovec *iov, int nr_segs) > { > for (seg = 0; seg < nr_segs; seg++) { > void __user *buf = iov[seg].iov_base; > ssize_t len = (ssize_t)iov[seg].iov_len; > > if (unlikely(!access_ok(buf, len))) > return false; > } > return true; > } You really don't want to be looping through the array twice. In fact you don't really want to be doing all those tests at all. This code makes a significant fraction of the not-insignificant difference between the 'costs' of send() and sendmsg(). I think the 'length' check can be optimised to do something like: for (...) { ssize_t len = (ssize_t)iov[seg].iov_len; ret += len; len_hi += (unsigned long)len >> 20; } if (len_hi) { /* Something potentially odd in the lengths. * Might just be a very long fragment. * Check the individial values. */ Add the exiting loop here. } David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel