Messages in this thread | | | Date | Mon, 19 Oct 2020 22:39:35 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH 3/5] x86/boot/compressed/64: Check SEV encryption in 64-bit boot-path |
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On Mon, Oct 19, 2020 at 01:54:47PM -0400, Arvind Sankar wrote: > Also, isn't it possible that the initial page tables we're running on > have already been messed with and have the C-bit in the wrong location, > so that this write happens decrypted?
The code assumes that the page-table it is running on has the correct C bit position set and that the code which set it up verified that it is correct. For the kernel itself this is true, at least, but when booting via UEFI the check also needs to happen in the firmware.
Note that the possibilies are limited when the hypervisor reports the wrong C bit position because code fetches always assume encryption, even when the C bit is cleared in the page-table. So a wrong C bit position in the decompression stub would write the kernel image to memory unencrypted and executing it would not be possible.
Regards,
Joerg
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