linux-kernel - Re: [PATCH v3 2/2] x86/devmem: Drop /dev/mem access for confidential guests

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Message-ID: <73f393a9-32e4-4f39-9834-249068ca3294@intel.com>
Date: Thu, 17 Apr 2025 12:33:30 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Dan Williams <dan.j.williams@...el.com>, dave.hansen@...ux.intel.com
Cc: x86@...nel.org, Kees Cook <kees@...nel.org>,
 Ingo Molnar <mingo@...nel.org>, Naveen N Rao <naveen@...nel.org>,
 Vishal Annapurve <vannapurve@...gle.com>,
 Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
 Nikolay Borisov <nik.borisov@...e.com>, stable@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev
Subject: Re: [PATCH v3 2/2] x86/devmem: Drop /dev/mem access for confidential
 guests

On 4/17/25 12:12, Dan Williams wrote:
...
> +	/*
> +	 * Enforce encrypted mapping consistency and avoid unaccepted
> +	 * memory conflicts, "lockdown" /dev/mem for confidential
> +	 * guests.
> +	 */
> +	if (IS_ENABLED(CONFIG_STRICT_DEVMEM) &&
> +	    cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
> +		return -EPERM;
> +
A lot of /dev/mem use seems to be poking at random hardware details like
BIOS internals, ACPI tables or hardware devices. Those all have modern
alternatives. So while I worry that this will make some userspace mad, I
have a hard time imagining that it's _relevant_ userspace on a modern
x86 CoCo platform where that userspace isn't buggy already.

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>