netdev - Re: [RFC PATCH 0/3] kernel: add support for 256-bit IO access

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]

Date:   Mon, 19 Mar 2018 09:29:19 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "ganeshgr@...lsio.com" <ganeshgr@...lsio.com>,
        "nirranjan@...lsio.com" <nirranjan@...lsio.com>,
        "indranil@...lsio.com" <indranil@...lsio.com>
Subject: Re: [RFC PATCH 0/3] kernel: add support for 256-bit IO access

On Mon, Mar 19, 2018 at 8:53 AM, David Laight <David.Laight@...lab.com> wrote:
>
> The x87 and SSE registers can't be changed - they can contain callee-saved
> registers.
> But (IIRC) the AVX and AVX2 registers are all caller-saved.

No.

The kernel entry is not the usual function call.

On kernel entry, *all* registers are callee-saved.

Of course, some may be return values, and I have a slight hope that I
can trash %eflags. But basically, a system call is simply not a
function call. We have different calling conventions on the argument
side too. In fact, the arguments are in different registers depending
on just *which* system call you take.

                  Linus