Re: [PATCH 0/2] wireguard-linux-compat: grsecurity compat patches

[Aymeric Fromherz <aymeric.fromherz@inria.fr>]

Hi Mathias,

Thanks for the comments. Unfortunately, changing "r" to "rm" for the out parameter in a systematic way is quite trick.
Allowing arguments to be passed independently in a register or in memory is currently out of scope of the Vale model we use for verification.
We must decide early on in the verification pipeline if the argument is passed in a register, or if it stored in memory.
Doing this in a sound way would require a significant change to our (trusted) model.

Cheers,
Aymeric

----- Mail original -----
> De: "Mathias Krause" <minipli@grsecurity.net>
> À: "Aymeric Fromherz" <aymeric.fromherz@inria.fr>, "Jason A. Donenfeld" <Jason@zx2c4.com>
> Cc: "WireGuard mailing list" <wireguard@lists.zx2c4.com>
> Envoyé: Lundi 13 Décembre 2021 08:44:51
> Objet: Re: [PATCH 0/2] wireguard-linux-compat: grsecurity compat patches

> Hi Aymeric,
> 
> the changes look good to me -- quite what we already had in grsec. Just
> one more nit. The constraints for the 'out' parameter in fmul(),
> fmul2(), fsqr() and fsqr2() can be further lifted to "rm" as 'out' is
> only referenced once. This allows gcc to choose either a register or a
> memory operand, as it sees fit. In our experiments the latter lead to
> much better code gen.
> 
> Thanks,
> Mathias
> 
> Am 11.12.21 um 17:35 schrieb Aymeric Fromherz:
>> Thanks for the heads-up. We were being overly conservative during verification
>> of inline assembly code in Vale, and marked several registers as possibly
>> modified while they were only read.
>> 
>> This is now fixed for fmul, fmul2, fsqr and fsqr2, and will be merged into the
>> master branch of EverCrypt shortly.
>> In the meantime, the diff for the resulting inline assembly after Vale codegen
>> is available here:
>> https://github.com/project-everest/hacl-star/pull/501/commits/1a71adb40c3f78da16e16975dbb1d4de5adeab8c#diff-5aabe9f6aa87508c9d81d4c9e89eff0b06b1e2aeaf5b04eba51da71c5bea6940
>> 
>> Cheers,
>> Aymeric
>> 
>> ----- Mail original -----
>>> De: "Jason A. Donenfeld" <Jason@zx2c4.com>
>>> À: "Mathias Krause" <minipli@grsecurity.net>, "aymeric fromherz"
>>> <aymeric.fromherz@inria.fr>
>>> Cc: "WireGuard mailing list" <wireguard@lists.zx2c4.com>
>>> Envoyé: Vendredi 10 Décembre 2021 23:58:01
>>> Objet: Re: [PATCH 0/2] wireguard-linux-compat: grsecurity compat patches
>> 
>>> CC'ing in Aymeric, who's working on Vale's codegen.
>>>
>>> On Thu, Dec 9, 2021 at 8:59 AM Mathias Krause <minipli@grsecurity.net> wrote:
>>>>
>>>> Am 08.12.21 um 15:56 schrieb Jason A. Donenfeld:
>>>>> On Mon, Dec 6, 2021 at 10:00 PM Mathias Krause <minipli@grsecurity.net> wrote:
>>>>>> Yes, probably, but you're mixing up the two.
>>>>>
>>>>> Oh, thanks, right.
>>>>>
>>>>> I'll talk to EverCrypt upstream and see.
>>>>
>>>> FWIW, 'out' is also wrongly flagged as output operand in fmul() and
>>>> fmul2(). But making it an input operand needs more surgery, as the
>>>> operand order changes and this requires some code churn.
>>>>
> >>> Mathias