linux-hardening - Re: [PATCH v3 00/24] x86_64: Improvements at compressed kernel stage

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Message-ID: <20221213181336.fjyxagxkjtq3jchl@redhat.com>
Date:   Tue, 13 Dec 2022 13:13:37 -0500
From:   Peter Jones <pjones@...hat.com>
To:     Evgeniy Baskov <baskov@...ras.ru>
Cc:     Ard Biesheuvel <ardb@...nel.org>, 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>,
        "Limonciello, Mario" <mario.limonciello@....com>,
        joeyli <jlee@...e.com>, 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 v3 00/24] x86_64: Improvements at compressed kernel stage

On Tue, Dec 13, 2022 at 01:03:17PM -0500, Peter Jones wrote:
> On Tue, Nov 22, 2022 at 02:12:09PM +0300, Evgeniy Baskov wrote:
> > This patchset is aimed
> > * to improve UEFI compatibility of compressed kernel code for x86_64
> > * to setup proper memory access attributes for code and rodata sections
> > * to implement W^X protection policy throughout the whole execution 
> >   of compressed kernel for EFISTUB code path. 
> 
> Hi Evgeniy,
> 
> I've tested this patch set on hardware and QEMU+MU firmware, and it
> works for me with a couple of minor issues:
> 
> - on one machine that has the DXE protocol but not the EFI one, we get
>   an error because the firmware doesn't support EFI_MEMORY_RP
> - on QEMU I'm seeing the size of "(unsigned long)_head - image_base"
>   wind up as 0, which leads to an EFI_INVALID_PARAMETER on the
>   clear_memory_attributes() call.
> 
> In both cases the system winds up working, but with unnecessary console
> output.

I just realized I've overstated here - I haven't actually hit the first
problem on x86, only on ARM, where we don't currently use this code.  I
discovered it in grub, and checked your patch set to see if you had the
same issue I did.  That said, "in both cases the system winds up
working" is probably still true - in that the edk2 code supports
EFI_MEMORY_RP on x86 but not ARM, so x86 won't hit the issue when using
DXE unless someone cooks up another implementation.  Nevertheless I
believe the patch to fix it is correct and should be applied.

Thanks!

-- 
        Peter