On Fri, Jul 17, 2020 at 4:05 PM Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 7/17/20 7:48 AM, Dmitry Vyukov wrote: > > On Sat, Jul 11, 2020 at 6:16 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > >> > >> On Sat, Jul 11, 2020 at 5:52 PM Hristo Venev <hristo@xxxxxxxxxx> wrote: > >>> > >>> On Sat, 2020-07-11 at 17:31 +0200, Dmitry Vyukov wrote: > >>>> Looking at the code more, I am not sure how it may not corrupt > >>>> memory. > >>>> There definitely should be some combinations where accessing > >>>> sq_entries*sizeof(u32) more memory won't be OK. > >>>> May be worth adding a test that allocates all possible sizes for > >>>> sq/cq > >>>> and fills both rings. > >>> > >>> The layout (after the fix) is roughly as follows: > >>> > >>> 1. struct io_rings - ~192 bytes, maybe 256 > >>> 2. cqes - (32 << n) bytes > >>> 3. sq_array - (4 << n) bytes > >>> > >>> The bug was that the sq_array was offset by (4 << n) bytes. I think > >>> issues can only occur when > >>> > >>> PAGE_ALIGN(192 + (32 << n) + (4 << n) + (4 << n)) > >>> != > >>> PAGE_ALIGN(192 + (32 << n) + (4 << n)) > >>> > >>> It looks like this never happens. We got lucky. > >> > >> Interesting. CQ entries are larger and we have at least that many of > >> them as SQ entries. I guess this + power-of-2-pages can make it never > >> overflow. > > > > Hi Jens, > > > > I see this patch is in block/for-5.9/io_uring > > Is this tree merged into linux-next? I don't see it in linux-next yet. > > Or is it possible to get it into 5.8? > > Yes, that tree is in linux-next, and I'm surprised you don't see it there > as it's been queued up for almost a week. Are you sure? > > I'm not going to apply it to both 5.9 and 5.8 trees. The bug has > been there for a while, but doesn't really impact functionality. > Hence I just queued it up for 5.9. If this had been a 5.8 commit > that introduced it, I would have queued it up for 5.8. > > > The reason I am asking is that we have an intern (Necip in CC) working > > on significantly extending io_uring coverage in syzkaller: > > https://github.com/google/syzkaller/pull/1926 > > Unfortunately we had to hardcode offset computation logic b/c the > > intended way of using io_uring for normal programs represents an > > additional obstacle for the fuzzer and the relations between syscalls > > and writes to shared memory are even hard to express for the fuzzer. > > We want to hardcode this new updated way of computing offsets, but > > this means we probably won't get good coverage until the intern term > > ends (+ may be good to discover some io_uring bugs before the > > release). > > Sounds good > > > If it won't get into linux-next/mainline until 5.9, it's not a big > > deal, but I wanted to ask. > > That's the plan, it'll go in as part of the 5.9 merge window. Thanks. linux-next is good enough, we test it. And the commit is actually already there, now that I looked closer.
