linux-kernel - Re: [PATCH v2] x86/sme: Explicitly map new EFI memmap table as encrypted

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Date:   Wed, 27 Oct 2021 17:14:35 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "# 3.4.x" <stable@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH v2] x86/sme: Explicitly map new EFI memmap table as encrypted

On Wed, 27 Oct 2021 at 17:11, Tom Lendacky <thomas.lendacky@....com> wrote:
>
> On 10/22/21 12:02 PM, Tom Lendacky wrote:
> > Reserving memory using efi_mem_reserve() calls into the x86
> > efi_arch_mem_reserve() function. This function will insert a new EFI
> > memory descriptor into the EFI memory map representing the area of
> > memory to be reserved and marking it as EFI runtime memory.
> >
> > As part of adding this new entry, a new EFI memory map is allocated and
> > mapped. The mapping is where a problem can occur. This new EFI memory map
> > is mapped using early_memremap(). If the allocated memory comes from an
> > area that is marked as EFI_BOOT_SERVICES_DATA memory in the current EFI
> > memory map, then it will be mapped unencrypted (see memremap_is_efi_data()
> > and the call to efi_mem_type()).
> >
> > However, during replacement of the old EFI memory map with the new EFI
> > memory map, efi_mem_type() is disabled, resulting in the new EFI memory
> > map always being mapped encrypted in efi.memmap. This will cause a kernel
> > crash later in the boot.
> >
> > Since it is known that the new EFI memory map will always be mapped
> > encrypted when efi_memmap_install() is called, explicitly map the new EFI
> > memory map as encrypted (using early_memremap_prot()) when inserting the
> > new memory map entry.
> >
> > Cc: <stable@...r.kernel.org> # 4.14.x
> > Fixes: 8f716c9b5feb ("x86/mm: Add support to access boot related data in the clear")
> > Acked-by: Ard Biesheuvel <ardb@...nel.org>
> > Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>
> Ard, are you going to take this through the EFI tree or does it need to go
> through another tree?
>

I could take it, but since it will ultimately go through -tip anyway,
perhaps better if they just take it directly? (This will change after
the next -rc1 though)

Boris?