linux-kernel - Re: [RFC PATCH v1 10/18] x86/efi: Access EFI related tables in the clear

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Message-ID: <5762B9E7.80903@amd.com>
Date:	Thu, 16 Jun 2016 09:38:31 -0500
From:	Tom Lendacky <thomas.lendacky@....com>
To:	Matt Fleming <matt@...eblueprint.co.uk>
CC:	<linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
	<kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
	<iommu@...ts.linux-foundation.org>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Jonathan Corbet <corbet@....net>,
	Joerg Roedel <joro@...tes.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Alexander Potapenko <glider@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v1 10/18] x86/efi: Access EFI related tables in the
 clear

On 06/15/2016 08:17 AM, Tom Lendacky wrote:
> On 06/13/2016 08:51 AM, Matt Fleming wrote:
>> On Thu, 09 Jun, at 01:33:30PM, Tom Lendacky wrote:
>>>

[...]

>>
>>> I'll look further into this, but I saw that this area of virtual memory
>>> was mapped un-encrypted and after freeing the boot services the
>>> mappings were somehow reused as un-encrypted for DMA which assumes
>>> (unless using swiotlb) encrypted. This resulted in DMA data being
>>> transferred in as encrypted and then accessed un-encrypted.
>>
>> That the mappings were re-used isn't a surprise.
>>
>> efi_free_boot_services() lifts the reservation that was put in place
>> during efi_reserve_boot_services() and releases the pages to the
>> kernel's memory allocators.
>>
>> What is surprising is that they were marked unencrypted at all.
>> There's nothing special about these pages as far as the __va() region
>> is concerned.
> 
> Right, let me keep looking into this to see if I can pin down what
> was (or is) happening.

Ok, I think this was happening before the commit to build our own
EFI page table structures:

commit 67a9108ed ("x86/efi: Build our own page table structures")

Before this commit the boot services ended up mapped into the kernel
page table entries as un-encrypted during efi_map_regions() and I needed
to change those entries back to encrypted. With your change above,
this appears to no longer be needed.

Thanks,
Tom

> 
> Thanks,
> Tom
> 
>>