On 7/17/20 8:05 AM, Jens Axboe 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 see it in there: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/fs/io_uring.c?id=a4968ff8b6314631a73fdc945a66fd8645dfe8cc -- Jens Axboe
