[edk2-devel] EFI table being corrupted during Kexec

[Breno Leitao <leitao@debian.org>]

We've seen a problem in upstream kernel kexec, where a EFI TPM log event table
is being overwritten.  This problem happen on real machine, as well as in a
recent EDK2 qemu VM.

Digging deep, the table is being overwritten during kexec, more precisely when
relocating kernel (relocate_kernel() function).

I've also found that the table is being properly reserved using
memblock_reserve() early in the boot, and that range gets overwritten later in
by relocate_kernel(). In other words, kexec is overwriting a memory that was
previously reserved (as memblock_reserve()).

Usama found that kexec only honours memory reservations from /sys/firmware/memmap
which comes from e820_table_firmware table.

Looking at the TPM spec, I found the following part:

	If the ACPI TPM2 table contains the address and size of the Platform Firmware TCG log,
	firmware “pins” the memory associated with the Platform Firmware TCG log, and reports
	this memory as “Reserved” memory via the INT 15h/E820 interface.


From: https://trustedcomputinggroup.org/wp-content/uploads/PC-ClientPlatform_Profile_for_TPM_2p0_Systems_v49_161114_public-review.pdf

I am wondering if that memory region/range should be part of e820 table that is
passed by EFI firmware to kernel, and if it is not passed (as it is not being
passed today), then the kernel doesn't need to respect it, and it is free to
overwrite (as it does today). In other words, this is a firmware bug and not a
kernel bug.

Am I missing something?

Thanks
--breno


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