linux-kernel - Re: [PATCH v1 4/4] xen/netback: Fix grant copy across page boundary with KASAN

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Message-ID: <e0663153-35e0-32ef-87a5-39189c440a3d@citrix.com>
Date:   Wed, 15 Jan 2020 11:02:59 +0000
From:   Sergey Dyasli <sergey.dyasli@...rix.com>
To:     Vlastimil Babka <vbabka@...e.cz>, <xen-devel@...ts.xen.org>,
        <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
CC:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        "Stefano Stabellini" <sstabellini@...nel.org>,
        George Dunlap <george.dunlap@...rix.com>,
        Ross Lagerwall <ross.lagerwall@...rix.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wei Liu <wei.liu@...nel.org>, "Paul Durrant" <paul@....org>,
        "sergey.dyasli@...rix.com >> Sergey Dyasli" 
        <sergey.dyasli@...rix.com>
Subject: Re: [PATCH v1 4/4] xen/netback: Fix grant copy across page boundary
 with KASAN

On 09/01/2020 10:33, Vlastimil Babka wrote:
> On 1/8/20 4:21 PM, Sergey Dyasli wrote:
>> From: Ross Lagerwall <ross.lagerwall@...rix.com>
>>
>> When KASAN (or SLUB_DEBUG) is turned on, the normal expectation that
>> allocations are aligned to the next power of 2 of the size does not
>> hold.
>
> Hmm, really? They should after 59bb47985c1d ("mm, sl[aou]b: guarantee
> natural alignment for kmalloc(power-of-two)"), i.e. since 5.4.
>
> But actually the guarantee is only for precise power of two sizes given
> to kmalloc(). Allocations of sizes that end up using the 96 or 192 bytes
> kmalloc cache have no such guarantee. But those might then cross page
> boundary also without SLUB_DEBUG.

That's interesting to know. It's certainly not the case for 4.19 kernel
for which PV KASAN was initially developed. But I guess this means that
only patch description needs updating.

>
>> Therefore, handle grant copies that cross page boundaries.
>>
>> Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
>> Signed-off-by: Sergey Dyasli <sergey.dyasli@...rix.com>

--
Thanks,
Sergey