[edk2-devel] EFI table being corrupted during Kexec

[Andrew (EFI) Fish]

> On Sep 10, 2024, at 6:58 AM, Breno Leitao <leitao at debian.org> wrote:
> 
> 
> 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.
> 

The E820 table is not part of the UEFI standard and it is produced by a library in the OvmfPkg for “special cases” so I guess that lib could have a bug?

> 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.
> 

INT 15h is Legacy BIOS not UEFI. For UEFI there is just the UEFI memory map and ACPI. 

Thanks,

Andrew Fish


> 
> 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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