linux-kernel - Re: [PATCH v2] x86: bring back rep movsq for user access on CPUs without ERMS

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAGudoHENT1yPBD=+xAUTzWxL+iro8CE3+hHLtYiU6j3cCv7PPA@mail.gmail.com>
Date:   Mon, 4 Sep 2023 08:03:34 +0200
From:   Mateusz Guzik <mjguzik@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, bp@...en8.de
Subject: Re: [PATCH v2] x86: bring back rep movsq for user access on CPUs
 without ERMS

On 9/4/23, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Sun, 3 Sept 2023 at 20:07, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> Try it and you'll see it is not even *remotely* as easy as you claim.
>> Not when you have to deal with random sizes and padding of 20+
>> different architectures.
>
> Perhaps more importantly, nobody actually seems to have the energy to care.
>

Perhaps in this context I should have explicitly mentioned that only
64-bit archs would be considered, as in placing the func you wrote in
fs/stat.c and it is explicitly 64-bit. This should whack all archs
which would never bother with their implementation anyway.

Worst case if the 64 bit structs differ one can settle for
user-accessing INIT_STRUCT_STAT_PADDING.

My point though was that code filling the struct escaping to
arch-dependent file is rather regrettable, even if x86-64 would be the
only case. And it definitely can be avoided, even if would require
tolerating that some of the stores are reordered. They are already
reordered for dodging memset.

-- 
Mateusz Guzik <mjguzik gmail.com>