linux-kernel - Re: [PATCH v2] mm: userfaultfd: avoid passing an invalid range to vma

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Message-ID: <ZGKmjUL5etmvIouh@x1n>
Date:   Mon, 15 May 2023 17:39:25 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Lorenzo Stoakes <lstoakes@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v2] mm: userfaultfd: avoid passing an invalid range to
 vma_merge()

On Mon, May 15, 2023 at 08:32:32PM +0100, Lorenzo Stoakes wrote:
> As well as fixing the repro described in [1] this also continues to pass
> uffd unit tests.

Side note on testing, not directly relevant to the patch itself..

I'm wondering whether do we have tests somewhere to just test vma
operations on split and merge, then verify it using smap or whatever.

The uffd unit test in this case is probably not gonna trigger anything
because we always mostly register with a whole vma over the testing ranges,
so not immediately helpful.

The trick here is we have quite a few ops that will call vma merge/split in
different ways, but logically we can still category them into: (1) add/del
vmas, or (2) modify vma flags, so at least for case (2) we can have a
framework to cover all the cases (mbind, mprotect, uffd reg/unreg, mlock,
etc.), the difference will be the flags we'll be looking at for different
cases, however how vmas merge/split should be somehow in the same pattern.

-- 
Peter Xu