linux-kernel - Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch

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-=wh5sTSF0X7qp80Ls5QZ2AgAm3yk3Ow9qOuNKB6O_zGVKA@mail.gmail.com>
Date:   Fri, 15 Feb 2019 16:21:46 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Brian Gerst <brgerst@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-alpha@...r.kernel.org" <linux-arm-kernel@...ts.infradead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        "H. Peter Anvin" <hpa@...or.com>, valentin.schneider@....com,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch

On Fri, Feb 15, 2019 at 3:34 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Now, EFLAGS bit 1 is supposedly always 1, but it really doesn't seem to
> matter for POPF.

Correct, it's "read as 1", you can try to write it and it doesn't matter.

> I went through the other flags, and aside from VIP/VIF (I've no clue),
> they looks like 0 should be just fine.

So 0 is a perfectly valid initializer in the sense that it _works_, I
just want it to be something that was thought about, not just a random
"initialize to zero" without thinking.

Even just a comment about it would be fine. But it might also be good
to show that it's an explicit eflags value and just use
X86_EFLAGS_FIXED as the initializer.

            Linus