linux-kernel - Re: [PATCH] x86/cpu, x86/pti: Do not enable PTI on AMD processors

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Message-ID: <20180212152630.GD13962@amd>
Date:   Mon, 12 Feb 2018 16:26:30 +0100
From:   Pavel Machek <pavel@....cz>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH] x86/cpu, x86/pti: Do not enable PTI on AMD processors

On Tue 2017-12-26 23:43:54, Tom Lendacky wrote:
> AMD processors are not subject to the types of attacks that the kernel
> page table isolation feature protects against.  The AMD microarchitecture
> does not allow memory references, including speculative references, that
> access higher privileged data when running in a lesser privileged mode
> when that access would result in a page fault.
> 
> Disable page table isolation by default on AMD processors by not setting
> the X86_BUG_CPU_INSECURE feature, which controls whether X86_FEATURE_PTI
> is set.

PTI was originally meant to protect KASLR from memory leaks, before
Spectre was public. I guess that's still valid use on AMD cpus?
								Pavel
								
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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