Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
Date:   Thu, 03 Mar 2022 17:15:46 +0300
From:   baskov@ispras.ru
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Matthew Garrett <mjg59@srcf.ucam.org>,
        Peter Jones <pjones@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        X86 ML <x86@kernel.org>, linux-efi <linux-efi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC v2 0/2] Handle UEFI NX-restricted page tables
In-Reply-To: <CAMj1kXGg=HAv3P_NKqUHCg6bRFsB0qhfa_z-TOdmi-G8EqPrZA@mail.gmail.com>
References: <20220224154330.26564-1-baskov@ispras.ru>
 <CAMj1kXGg=HAv3P_NKqUHCg6bRFsB0qhfa_z-TOdmi-G8EqPrZA@mail.gmail.com>
User-Agent: Roundcube Webmail/1.4.4
Message-ID: <773b799354b50adf854837d8a6d54b8f@ispras.ru>
Content-Type: text/plain; charset=US-ASCII;
 format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2022-02-28 19:45, Ard Biesheuvel wrote:
> (cc Matt and Peter)
> 
> 
> Thanks for exploring my suggestion to use the DXE services for this.
> 
> Given that this is a workaround for a very specific issue arising on
> PI based implementations of UEFI, I consider this a quirk, and so I
> think this approach is reasonable. I'd still like to gate it on some
> kind of identification, though - perhaps something related to DMI like
> the x86 core kernel does as well.
> 
> I've cc'ed Peter and Matt, who have much more experience dealing with
> these kinds of things on x86 - my experience is mostly based on ARM,
> which tends to be less quirky when it comes to UEFI support, given
> that vendors that implement EFI actually care about being compliant
> (instead of only about getting a windows sticker)
> 
> Matt, Peter, any thoughts?
> 
> 
>> Baskov Evgeniy (2):
>>        efi: declare DXE services table
>>        libstub: ensure allocated memory to be executable
>> 
>>  arch/x86/include/asm/efi.h              |  5 ++
>>  drivers/firmware/efi/libstub/efistub.h  | 53 ++++++++++++++++++++
>>  drivers/firmware/efi/libstub/x86-stub.c | 73 
>> ++++++++++++++++++++++++++--
>>  include/linux/efi.h                     |  2 +
>>  4 files changed, 128 insertions(+), 5 deletions(-)

We now have tested the patch on major platforms, and it works without 
any
issues. But in case of firmware bugs I have changed the code to only
modify attributes if either EFI_MEMORY_RO or EFI_MEMORY_WP is set and
the memory has type EfiGcdMemoryTypeSystemMemory.

I also added option CONFIG_EFI_DXE_MEM_ATTRIBUTES (enabled by default),
to allow this code to be disabled at compile time.

These changes will be sent in version 3 of the patch.

Thanks,
Baskov Evgeniy