linux-kernel - Re: Simplify load_unaligned_zeropad() (was Re: [GIT PULL] Ceph updates for 5.20-rc1)

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: <CAHk-=wiOqbuzy7xzsLrN8LXKGGUUMH109wcKOXx_PV9PkHa=Zw@mail.gmail.com>
Date:   Sun, 14 Aug 2022 15:59:42 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>, ceph-devel@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: Simplify load_unaligned_zeropad() (was Re: [GIT PULL] Ceph
 updates for 5.20-rc1)

On Sun, Aug 14, 2022 at 3:51 PM Kirill A. Shutemov <kirill@...temov.name> wrote:
>
> Do we gain enough benefit from the microoptimization to justify existing
> load_unaligned_zeropad()? The helper has rather confusing side-effects.

It's a *big* deal in pathname handling, yes. Doing things a byte at a
time is very noticeably slower.

If TDX has problems with it, then TDX needs to be fixed. And it's
simple enough - just make sure you have a guard page between any
kernel RAM mapping and whatever odd crazy page.

There is nothing subtle about this at all. You probably would want
that guard page *anyway*.

That "uaccepted memory" type needs to be just clearly fixed.

                Linus