linux-kernel - Re: LockDown that allows read of /dev/mem ?

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Message-ID: <d4c9740c-61ef-764a-b56e-7957cd26e12a@metux.net>
Date:   Fri, 2 Jul 2021 09:42:31 +0200
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     "David F." <df7729@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: LockDown that allows read of /dev/mem ?

On 21.06.21 17:29, David F. wrote:

Hi,

> Lockdown required by secure boot and shim signing (prevent acpi
> patching), root because it's main use is a utility boot disk.   If
> lockdown could be forced when secure boot active but not when not
> active, that be best, but I'm not seeing that option.  The other
> option maybe to modify open_port on mem.c to do the secure boot check.
> However searching EFI_SECURE_BOOT doesn't exist in 5.10.x as in
> efi_enabled(EFI_SECURE_BOOT) - It appears that is some other patch
> that is not applied to the base, I do see struct boot_params has a
> secure_boot field set, but can I access that from mem.c?  If not, is
> efi_get_secureboot() function available when /drivers/char/mem.c may
> be used?

I'd rather try not using /dev/mem at all.

What exactly do you really need it for, in that specific case ?


--mtx

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287