linux-kernel - Re: [PATCH v4 1/2] Avoid using EFI tables Xen may have clobbered

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Message-ID: <282a225d-8782-0321-6f0e-19dd4510dc42@suse.com>
Date:   Fri, 30 Sep 2022 08:44:21 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Demi Marie Obenour <demi@...isiblethingslab.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        linux-efi@...r.kernel.org, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
Subject: Re: [PATCH v4 1/2] Avoid using EFI tables Xen may have clobbered

On 30.09.2022 01:02, Demi Marie Obenour wrote:
> Memory of type EFI_CONVENTIONAL_MEMORY, EFI_LOADER_CODE, EFI_LOADER_DATA,
> EFI_BOOT_SERVICES_CODE, and EFI_BOOT_SERVICES_DATA may be clobbered by
> Xen before Linux gets to start using it.  Therefore, Linux under Xen
> must not use EFI tables from such memory.  Most of the remaining EFI
> memory types are not suitable for EFI tables, leaving only
> EFI_ACPI_RECLAIM_MEMORY, EFI_RUNTIME_SERVICES_DATA, and
> EFI_RUNTIME_SERVICES_CODE.  When running under Xen, Linux should only
> use tables that are located in one of these types of memory.
> 
> This patch ensures this, and also adds a function
> (xen_config_table_memory_region_max()) that will be used later to
> replace the usage of the EFI memory map in esrt.c when running under
> Xen.  This function can also be used in mokvar-table.c and efi-bgrt.c,
> but I have not implemented this.
> 
> Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>

In Xen we don't clobber EfiBootServices{Code,Data} when xen.efi was passed
"-mapbs". Should we perhaps extend the interface such that Dom0 can then
also use tables located in such regions, perhaps by faking
EFI_MEMORY_RUNTIME in the attributes returned by XEN_FW_EFI_MEM_INFO?

Jan