linux-kernel - Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS

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Message-ID: <20170426063556.vc2zmns3uscubuim@pd.tnic>
Date:   Wed, 26 Apr 2017 08:35:56 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, boris.ostrovsky@...cle.com, hpa@...or.com,
        tglx@...utronix.de, mingo@...hat.com
Subject: Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to
 zero

On Wed, Apr 26, 2017 at 06:45:42AM +0200, Juergen Gross wrote:
> The really clean solution would be to add this test to set_cpu_bug()

No, the really clean solution is to set it once and not play toggle
games.

> This would work. OTOH I'd prefer to test whether the bit should be
> forced to remain zero than use the knowledge _who_ is trying to force
> it.

Because we're in the business of investigating who did?

Nah, we should set it or clear it once and not do funky toggle games.
Especially if in the future something else changes and timing windows
grow and we refactor stuff and yadda yadda...

-- 
Regards/Gruss,
    Boris.

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