linux-kernel - Re: [PATCH v5 17/32] x86/mm: Add support to access boot related data in the clear

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Date:   Fri, 26 May 2017 11:22:36 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Matt Fleming <matt@...eblueprint.co.uk>,
        Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kasan-dev@...glegroups.com>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH v5 17/32] x86/mm: Add support to access boot related data
 in the clear

On 5/18/2017 2:50 PM, Matt Fleming wrote:
> On Mon, 15 May, at 08:35:17PM, Borislav Petkov wrote:
>> On Tue, Apr 18, 2017 at 04:19:21PM -0500, Tom Lendacky wrote:
>>
>>> +		paddr = boot_params.efi_info.efi_memmap_hi;
>>> +		paddr <<= 32;
>>> +		paddr |= boot_params.efi_info.efi_memmap;
>>> +		if (phys_addr == paddr)
>>> +			return true;
>>> +
>>> +		paddr = boot_params.efi_info.efi_systab_hi;
>>> +		paddr <<= 32;
>>> +		paddr |= boot_params.efi_info.efi_systab;
>>
>> So those two above look like could be two global vars which are
>> initialized somewhere in the EFI init path:
>>
>> efi_memmap_phys and efi_systab_phys or so.
>>
>> Matt ?
>>
>> And then you won't need to create that paddr each time on the fly. I
>> mean, it's not a lot of instructions but still...
>
> We should already have the physical memmap address available in
> 'efi.memmap.phys_map'.

Unfortunately memremap_is_efi_data() is called before the efi structure
gets initialized, so I can't use that value.

>
> And the physical address of the system table should be in
> 'efi_phys.systab'. See efi_init().

In addition to the same issue as efi.memmap.phys_map, efi_phys has
the __initdata attribute so it will be released/freed which will cause
problems in checks performed afterwards.

Thanks,
Tom

>