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From: Hristo Venev <hristo@venev.name>
To: Dmitry Vyukov <dvyukov@google.com>, Jens Axboe <axboe@kernel.dk>
Cc: Necip Fazil Yildiran <necip@google.com>, io-uring@vger.kernel.org
Subject: Re: [PATCH] io_uring: fix sq array offset calculation
Date: Sat, 11 Jul 2020 18:52:19 +0300	[thread overview]
Message-ID: <7f128319f405358aa448a869a3a634a6cbc1469f.camel@venev.name> (raw)
In-Reply-To: <CACT4Y+YGwr+1k=rsJhMsnyQL4C+S2s9t7Cz5Axwc9fO5Ap4HbQ@mail.gmail.com>

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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.

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  parent reply	other threads:[~2020-07-11 15:52 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-11  9:31 [PATCH] io_uring: fix sq array offset calculation Dmitry Vyukov
2020-07-11  9:37 ` Hristo Venev
2020-07-11 15:15 ` Jens Axboe
2020-07-11 15:31   ` Dmitry Vyukov
2020-07-11 15:36     ` Jens Axboe
2020-07-11 15:47       ` Jens Axboe
2020-07-11 15:52     ` Hristo Venev [this message]
2020-07-11 15:55       ` Jens Axboe
2020-07-11 15:56       ` Hristo Venev
2020-07-11 16:16       ` Dmitry Vyukov
2020-07-17 13:48         ` Dmitry Vyukov
2020-07-17 14:05           ` Jens Axboe
2020-07-17 14:08             ` Jens Axboe
2020-07-17 14:08             ` Dmitry Vyukov

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