linux-kernel - Re: [GIT PULL] Enable -Wstringop-overflow globally

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Message-ID: <0c4cc1a7-f409-4597-b110-81f9e45d1ffe@embeddedor.com>
Date: Sat, 27 Jan 2024 13:53:00 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: David Laight <David.Laight@...LAB.COM>,
 'Linus Torvalds' <torvalds@...ux-foundation.org>,
 Kees Cook <keescook@...omium.org>, Lucas De Marchi
 <lucas.demarchi@...el.com>, Oded Gabbay <ogabbay@...nel.org>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 intel-xe@...ts.freedesktop.org,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [GIT PULL] Enable -Wstringop-overflow globally

On 1/27/24 09:11, David Laight wrote:
> From: Linus Torvalds
>> Sent: 26 January 2024 22:36
>>
>> On Fri, 26 Jan 2024 at 14:24, Kees Cook <keescook@...omium.org> wrote:
>>>
>>> I think xe has some other weird problems too. This may be related (under
>>> allocating):
>>>
>>> ../drivers/gpu/drm/xe/xe_vm.c: In function 'xe_vma_create':
>>> ../drivers/gpu/drm/xe/xe_vm.c:806:21: warning: allocation of insufficient size '224' for type
>> 'struct xe_vma' with size '368' [-Walloc-size]
>>>    806 |                 vma = kzalloc(sizeof(*vma) - sizeof(struct xe_userptr),
>>>        |                     ^
>>
>> That code is indeed odd, but there's a comment in the xe_vma definition
>>
>>          /**
>>           * @userptr: user pointer state, only allocated for VMAs that are
>>           * user pointers
>>           */
>>          struct xe_userptr userptr;
>>
>> although I agree that it should probably simply be made a final
>> variably-sized array instead (and then you make that array size be
>> 0/1).
> 
> That entire code is odd.
> It isn't obvious that the flag values that cause the short allocate
> are the same ones that control whether the extra data is accessed.
> 
> Never mind the oddities with the 'flags |= ' assignments int the
> 'remap next' path.
> 
> Anyone know how many of these actually get allocated (and their
> lifetimes)?
> How much difference would it make to allocate 368 (maybe 384?)
> bytes instead of 224 (likely 256).

[CC+ xen list and maintainers]

Probably the xen maintainer can help us out here.

--
Gustavo

> 
> 	David
> 
> -
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