linux-kernel - Re: [RFC PATCH] x86/pkeys: update PKRU to enable pkey 0 before XSAVE

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Message-ID: <4bd2aea0-3cea-4ef8-9607-40447cd531e5@intel.com>
Date: Thu, 14 Mar 2024 10:54:18 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>,
 linux-kernel@...r.kernel.org
Cc: x86@...nel.org, dave.hansen@...ux.intel.com, tglx@...utronix.de
Subject: Re: [RFC PATCH] x86/pkeys: update PKRU to enable pkey 0 before XSAVE

On 3/14/24 10:29, Aruna Ramakrishna wrote:
> This patch is a workaround for a bug where the PKRU value is not
> restored to the init value before the signal handler is invoked.

I don't think we should touch this with a ten foot pole without a test
for it in tools/testing/selftests/mm/protection_keys.c.

I'm not sure this is worth the trouble.  Protection keys is not a
security feature.  This isn't a regression.  It's been the behavior
since day one.  This really is a feature request for a behavioral
improvement, not a bug fix.

The need for this new feature is highly dependent on the threat model
that it supports.  I'm highly dubious that there's a true need to
protect against an attacker with arbitrary write access in the same
address space.  We need to have a lot more information there.

I haven't even more than glanced at the code.  It looks pretty
unspeakably ugly even at a glance.