Re: [PATCH 4/7] x86: Add SSSE3 optimized chacha20

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 14/04/2022 14:17, Noah Goldstein wrote:
> On Wed, Apr 13, 2022 at 3:27 PM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
>>
>> +       clear(X1);
>> +       clear(X2);
>> +       clear(X3);
>> +       clear(X4);
>> +       clear(X5);
>> +       clear(X6);
>> +       clear(X7);
>> +       clear(X8);
>> +       clear(X9);
>> +       clear(X10);
>> +       clear(X11);
>> +       clear(X12);
>> +       clear(X13);
>> +       clear(X14);
>> +       clear(X15);
> 
> No need to change now, but out of curiosity (and possible future optimization),
> do we need the clears for our purposes?

That's a good question which I am not sure.  Distro do usually build glibc
with security options (such as stack protector and stack check) and keep
adding support for newer CPU security hardening (such as ARM PAC/BIT or
Intel CET). 

We also uses some more software oriented hardening, such as explicit_memset
on some places.

I would expect that distro might use -mharden-sls, but I am not sure if
we should enforce it on all assembly implementations.