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:

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On Thu, 09 Jun, at 01:33:30PM, Tom Lendacky wrote:

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[...]

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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

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