linux-hardening - Re: [PATCH 04/16] x86/boot: Increase boot page table size

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Date:   Thu, 20 Oct 2022 14:29:24 +0300
From:   Evgeniy Baskov <baskov@...ras.ru>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        lvc-project@...uxtesting.org, x86@...nel.org,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 04/16] x86/boot: Increase boot page table size

On 2022-10-19 10:08, Ard Biesheuvel wrote:
> On Tue, 6 Sept 2022 at 12:41, Evgeniy Baskov <baskov@...ras.ru> wrote:
>> 
>> Previous calculations ignored pages implicitly mapped by ACPI code,
> 
> I'm not sure I understand what this means. Which ACPI code and which
> pages does it map?

Code from boot/compressed/{acpi.c,efi.c} that touches ACPI/EFI tables
is currently mapping pages that contain the tables implicitly by
causing page faults. And those mappings may require additional
memory for page tables. It became more apparent when I were removing
memory mapping from page fault handler.

> 
>> so theoretical upper limit is higher than was set.
...