linux-hardening - Re: [PATCH net-next v3 1/7] overflow: add DEFINE

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Date:   Mon, 28 Aug 2023 16:41:15 +0200
From:   Przemek Kitszel <przemyslaw.kitszel@...el.com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Kees Cook' <keescook@...omium.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jacob Keller <jacob.e.keller@...el.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        Alexander Lobakin <aleksander.lobakin@...el.com>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        Steven Zou <steven.zou@...el.com>
Subject: Re: [PATCH net-next v3 1/7] overflow: add DEFINE_FLEX() for on-stack
 allocs

On 8/23/23 22:52, Przemek Kitszel wrote:
> On 8/18/23 12:49, David Laight wrote:
>> From: Przemek Kitszel
>>> Sent: Friday, August 18, 2023 11:28 AM
>> ...
>>>>>> I'm not sure you should be forcing the memset() either.
>>>>>
>>>>> This already got discussed: better to fail safe.
>>>>
>>>> Perhaps call it DEFINE_FLEX_Z() to make this clear and
>>>> give the option for a non-zeroing version later.
>>>> Not everyone wants the expense of zeroing everything.
>>>
>>> per Kees, zeroing should be removed by compiler when not needed:
>>> https://lore.kernel.org/intel-wired-lan/202308101128.C4F0FA235@keescook/
>>
>> Expect in the most trivial cases the compiler is pretty much never
>> going to remove the zeroing of the data[] part.
>>
>> I'm also not at all sure what happens if there is a function
>> call between the initialisation and any assignments.
>>
>> With a bit of effort you should be able to pass the '= {}'
>> through into an inner #define.
>> Possibly with the alternative of a caller-provider
>>   '= { .obj = call_supplied_initialiser }'
>> The 'not _Z' form would pass an empty argument.
>>
>>     David
> 
> Thanks, makes sense, there could be also DEFINE_FLEX_COUNTED
> (or DEFINE_FLEX_BOUNDED) to cover Kees's __counted_by() cases.
> 
> Would you like me to cover/convert any existing code/use cases (as with 
> other patches in the series, to have some examples/actual usage of newly 
> introduced macros)?

I did some manual searches and found no obvious candidate :/
will post next version/RFC without _NOINIT() variant.

> 
>>
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> 
>