linux-kernel - Re: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state

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Message-ID: <4f79864f-0278-0c06-54a5-84bb4f8a0ac0@intel.com>
Date:   Wed, 16 Jun 2021 09:17:12 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>, bp@...e.de,
        luto@...nel.org, tglx@...utronix.de, mingo@...nel.org,
        x86@...nel.org
Cc:     len.brown@...el.com, jing2.liu@...el.com, ravi.v.shankar@...el.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of
 dynamic user state

On 5/23/21 12:32 PM, Chang S. Bae wrote:
> Intel's Extended Feature Disable (XFD) feature is an extension of the XSAVE
> architecture. XFD allows the kernel to enable a feature state in XCR0 and
> to receive a #NM trap when a task uses instructions accessing that state.
> In this way, Linux can control the access to that state.

Please change the subject of this patch.  It's a crime to not have it
say XFD, "feature" or "disable".

I'd suggest:

	x86/fpu/xstate: use feature disable (XFD) to protect dynamic
			user state