linux-kernel - Re: [PATCH] sh: Implement __get_user_u64() required for 64-bit get

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: <fbfca28d-217d-4857-a010-8c6e277db67c@physik.fu-berlin.de>
Date:   Mon, 1 Jun 2020 11:13:26 +0200
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rich Felker <dalias@...c.org>
Cc:     Linux-sh list <linux-sh@...r.kernel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sh: Implement __get_user_u64() required for 64-bit
 get_user()

Hello!

On 6/1/20 11:02 AM, Geert Uytterhoeven wrote:
>> Can I propose a different solution? For archs where there isn't
>> actually any 64-bit load or store instruction, does it make sense to
>> be writing asm just to do two 32-bit loads/stores, especially when
>> this code is not in a hot path?
>>
>> What about just having the 64-bit versions call the corresponding
>> 32-bit version twice? (Ideally this would even be arch-generic and
>> could replace the m68k asm.) It would return EFAULT if either of the
>> 32-bit calls did.
> 
> Yes, that's an option, too.

That's the solution that Michael Karcher suggested to me as an alternative
when I talked to him off-list.

While I understand that it works, I don't like the inconsistency and I also
don't see why we should opt for a potentially slower solution when we can
used the fastest one.

I'm also not sure how the exception handling would properly work when you
have two invocations of __get_user_asm().

My current approach is consistent with the existing code, so I think it's
the natural choice. I just need someone with more experience in SH assembler
than me that the solution is correct.

I have already pinged Niibe-san in private, he'll hopefully get back to me
within the next days.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@...ian.org
`. `'   Freie Universitaet Berlin - glaubitz@...sik.fu-berlin.de
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913