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Date: Tue, 22 Sep 2020 10:57:11 +0300 From: Pavel Begunkov <asml.silence@...il.com> To: Arnd Bergmann <arnd@...db.de> Cc: Andy Lutomirski <luto@...nel.org>, Christoph Hellwig <hch@....de>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, David Howells <dhowells@...hat.com>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, "open list:MIPS" <linux-mips@...r.kernel.org>, Parisc List <linux-parisc@...r.kernel.org>, linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, linux-s390 <linux-s390@...r.kernel.org>, sparclinux <sparclinux@...r.kernel.org>, linux-block <linux-block@...r.kernel.org>, Linux SCSI List <linux-scsi@...r.kernel.org>, Linux FS Devel <linux-fsdevel@...r.kernel.org>, linux-aio <linux-aio@...ck.org>, io-uring@...r.kernel.org, linux-arch <linux-arch@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, Network Development <netdev@...r.kernel.org>, keyrings@...r.kernel.org, LSM List <linux-security-module@...r.kernel.org> Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag On 22/09/2020 10:23, Arnd Bergmann wrote: > On Tue, Sep 22, 2020 at 8:32 AM Pavel Begunkov <asml.silence@...il.com> wrote: >> On 22/09/2020 03:58, Andy Lutomirski wrote: >>> On Mon, Sep 21, 2020 at 5:24 PM Pavel Begunkov <asml.silence@...il.com> wrote: >>> I may be looking at a different kernel than you, but aren't you >>> preventing creating an io_uring regardless of whether SQPOLL is >>> requested? >> >> I diffed a not-saved file on a sleepy head, thanks for noticing. >> As you said, there should be an SQPOLL check. >> >> ... >> if (ctx->compat && (p->flags & IORING_SETUP_SQPOLL)) >> goto err; > > Wouldn't that mean that now 32-bit containers behave differently > between compat and native execution? > > I think if you want to prevent 32-bit applications from using SQPOLL, > it needs to be done the same way on both to be consistent: The intention was to disable only compat not native 32-bit. > > if ((!IS_ENABLED(CONFIG_64BIT) || ctx->compat) && > (p->flags & IORING_SETUP_SQPOLL)) > goto err; > > I don't really see how taking away SQPOLL from 32-bit tasks is > any better than just preventing access to the known-broken files > as Al suggested, or adding the hack to make it work as in > Christoph's original patch. That's why I'm hoping that Christoph's work and the discussion will reach consensus, but the bug should be patched in the end. IMHO, it's a good and easy enough fallback option (temporal?). > > Can we expect all existing and future user space to have a sane > fallback when IORING_SETUP_SQPOLL fails? SQPOLL has a few differences with non-SQPOLL modes, but it's easy to convert between them. Anyway, SQPOLL is a privileged special case that's here for performance/latency reasons, I don't think there will be any non-accidental users of it. -- Pavel Begunkov
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