linux-kernel - Re: [RFC PATCH] /dev/mem: Disable /dev/mem under TDX guest

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Message-ID: <auno67lcikllqdlgdsad72hvsmym4lqxnaqaohmvtvf2boscxu@54ftt6342jxy>
Date: Tue, 18 Mar 2025 15:27:48 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Nikolay Borisov <nik.borisov@...e.com>
Cc: dave.hansen@...ux.intel.com, linux-coco@...ts.linux.dev, 
	x86@...nel.org, linux-kernel@...r.kernel.org, vannapurve@...gle.com, 
	Elena Reshetova <elena.reshetova@...el.com>
Subject: Re: [RFC PATCH] /dev/mem: Disable /dev/mem under TDX guest

On Tue, Mar 18, 2025 at 02:53:34PM +0200, Nikolay Borisov wrote:
> > I think we need to think wider. What about applying a subset of LOCKDOWN_*
> > in all coco guests by default. Many of them are relevant for the guest security.
> 
> How do you envision this to work, by introducing another
> CONFIG_LOCK_DOWN_KERNEL_FORCE_COCO or some such ? Will it be opt-in or
> mandatory?

I think cc_platform_has(CC_ATTR_xxx) should enabled some subset of
LOCKDOWN_*. No need in new config options.

> Should we decide to follow the lockdown route this means the owner of the
> coco guest will have the ability to disable it and a misbehaving userspace
> process will still be able to induce an EPT violation.

Sure. It can shoot itself in the foot.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov