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In-Reply-To: From: Arnd Bergmann Date: Fri, 13 Dec 2019 22:32:48 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) To: Linus Torvalds Content-Type: text/plain; charset="UTF-8" X-Provags-ID: V03:K1:TGt8SMK++1Eqjof00YdGGjmEJz9TkBzo4vg6b97z5KFfwPrkXSW jnDLdvHpJDL/e+l6cIuiDRhtw2/xAySjvEvvlWVXUgDkvrlVDJlPIMfPzNZ4MsHZKU2C1iQ dCPIj9r9z9266sF4EtiTjSpOzH9dumvxVAhv9rHGssNqVOQoIYiooQ4Ths6R/HKx0j434gt uBf4v5AlZEFEGXGJY7eFQ== X-UI-Out-Filterresults: notjunk:1;V03:K0:Ds5O4DOc4hI=:Gg9BM7ra0nDyeKfr/VOkOR TM0E2D9QpkQGN+1zR1ONi12Mv69fSDRZ8BzFt2tC9ocUcl3bH3MXGmGObbRTNdzTzpyisJpJU fOPEJN3fmSreqz48fcmOmYa5nx2/iFRHqVxgOPhXw/QVh+CcuGHeEnqp9w1da7RJvm4QW85g9 Ue74XLQGjlH9qowgW4R8LQVDzkImsbb2PfjUM0XMVipHXU697DWmtGAQMuXMzuqR/CWAaatHZ YdRe+lOysOdGHsu+PS4HUCzvGKEzbXIDLh/F4ZO4Fdg+mtrYH0iNdhDT17V97wNFRaIUw5nHx Shth0I9r9l0pDga6bP6FmqEn/yP9PHHECf5dmDHZ4J9Ha2SDFNyBNpZZ6qvtVizUlM0G2D3dt C4KB26XrxBdvMgImsSn13CgvF/Y0roEMhgJfi5w5fTLkMqK8pSB7aeWw9G2rZu8N3FDe5W/Zc C/LO3yFeyarFThiM6/Sz7gAgBSc3vBlVlaBbB0rEnATRYhOWEICbqmZW5eK9l1QzF/v1DY9P7 vMYQKhlgiv/AxhwAobLI6JgKgHeLZPT7GGMiScADoYybb7AK7YoX5f4P0EO/1grgBVaCS0Oba IwNvitcxFDd9QaVDI+4ZhCB/5MksEVqrXZ06KYJDnUfbVoPD6hqfh0bHySrLIBzcF/BroGaB3 haxFH0R02wcvwNzzPLdsaiODaHuiuAPDlzPn4gnWVTgksW7l+a9SZu75cuzEnVca2f5+0KXnD B8DJu0v4puapm5slifaHm17paYwmCWmBcyt2Whm4LakFBiJt46tzJhOWtBV1WMgPmQprGOJEP T9a6tic7S8dPlSKXLxvUOcc03gnMKxO4hANt8JTNOSe7bkfi4QqAws2GkAJlDKEbeFqmKEqN7 8Qoe1D1vYWUO7ZI/IBHw== X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch , Will Deacon , Peter Zijlstra , Linux Kernel Mailing List , Christian Borntraeger , Mark Rutland , linuxppc-dev , Daniel Axtens Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, Dec 13, 2019 at 2:17 PM Arnd Bergmann wrote: > > On Thu, Dec 12, 2019 at 9:50 PM Linus Torvalds > wrote: > I'll have my randconfig builder look for instances, so far I found one, > see below. My feeling is that it would be better to enforce at least > the size being a 1/2/4/8, to avoid cases where someone thinks > the access is atomic, but it falls back on a memcpy. > > Arnd > > diff --git a/drivers/xen/time.c b/drivers/xen/time.c > index 0968859c29d0..adb492c0aa34 100644 > --- a/drivers/xen/time.c > +++ b/drivers/xen/time.c > @@ -64,7 +64,7 @@ static void xen_get_runstate_snapshot_cpu_delta( > do { > state_time = get64(&state->state_entry_time); > rmb(); /* Hypervisor might update data. */ > - *res = READ_ONCE(*state); > + memcpy(res, state, sizeof(*res)); > rmb(); /* Hypervisor might update data. */ > } while (get64(&state->state_entry_time) != state_time || > (state_time & XEN_RUNSTATE_UPDATE)); A few hundred randconfig (x86, arm32 and arm64) builds later I still only found one other instance: diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h index eddae4688862..1c1f33447e96 100644 --- a/net/xdp/xsk_queue.h +++ b/net/xdp/xsk_queue.h @@ -304,7 +304,9 @@ static inline struct xdp_desc *xskq_validate_desc(struct xsk_queue *q, struct xdp_rxtx_ring *ring = (struct xdp_rxtx_ring *)q->ring; unsigned int idx = q->cons_tail & q->ring_mask; - *desc = READ_ONCE(ring->desc[idx]); + barrier(); + memcpy(desc, &ring->desc[idx], sizeof(*desc)); + barrier(); if (xskq_is_valid_desc(q, desc, umem)) return desc; Arnd