linux-kernel - Re: [PATCH 0/6] efi/x86: Avoid legacy decompressor during EFI boot

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Message-ID: <CAMj1kXG8ZrdEUNTiSCet+aT+1ZyrbguFsGtNhVV+XgCssZgj9w@mail.gmail.com>
Date:   Tue, 2 May 2023 15:39:42 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Evgeniy Baskov <baskov@...ras.ru>,
        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>,
        Peter Jones <pjones@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        Mario Limonciello <mario.limonciello@....com>,
        Kees Cook <keescook@...omium.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/6] efi/x86: Avoid legacy decompressor during EFI boot

On Tue, 2 May 2023 at 15:37, Tom Lendacky <thomas.lendacky@....com> wrote:
>
> On 4/24/23 11:57, Ard Biesheuvel wrote:
> > This series is conceptually a combination of Evgeny's series [0] and
> > mine [1], both of which attempt to make the early decompressor code more
> > amenable to executing in the EFI environment with stricter handling of
> > memory permissions.
> >
> > My series [1] implemented zboot for x86, by getting rid of the entire
> > x86 decompressor, and replacing it with existing EFI code that does the
> > same but in a generic way. The downside of this is that only EFI boot is
> > supported, making it unviable for distros, which need to support BIOS
> > boot and hybrid EFI boot modes that omit the EFI stub.
> >
> > Evgeny's series [0] adapted the entire decompressor code flow to allow
> > it to execute in the EFI context as well as the bare metal context, and
> > this involves changes to the 1:1 mapping code and the page fault
> > handlers etc, none of which are really needed when doing EFI boot in the
> > first place.
> >
> > So this series attempts to occupy the middle ground here: it makes
> > minimal changes to the existing decompressor so some of it can be called
> > from the EFI stub. Then, it reimplements the EFI boot flow to decompress
> > the kernel and boot it directly, without relying on the trampoline code,
> > page table code or page fault handling code. This allows us to get rid
> > of quite a bit of unsavory EFI stub code, and replace it with two clear
> > invocations of the EFI firmware APIs to clear NX restrictions from
> > allocations that have been populated with executable code.
> >
> > The only code that is being reused is the decompression library itself,
> > along with the minimal ELF parsing that is required to copy the ELF
> > segments in place, and the relocation processing that fixes up absolute
> > symbol references to refer to the correct virtual addresses.
> >
> > Note that some of Evgeny's changes to clean up the PE/COFF header
> > generation will still be needed, but I've omitted those here for
> > brevity.
>
> I tried booting an SEV and an SEV-ES guest using this and both failed to boot:
>
> EFI stub: WARNING: Decompression failed: Out of memory while allocating
> z_stream
>
> I'll have to take a closer look as to why, but it might be a couple of
> days before I can get to it.
>

Thanks Tom.

The internal malloc() seems to be failing, which is often caused by
BSS clearing problems. Could you elaborate a little bit on the boot
environment you are using here?