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08 September 2024, 02:26:05 UTC
Revision 37926f96302d8b6c2bc97990d33e316a3ed6d67f authored by Ard Biesheuvel on 20 October 2022, 13:16:09 UTC, committed by Ard Biesheuvel on 21 October 2022, 09:09:41 UTC 
efi: runtime: Don't assume virtual mappings are missing if VA == PA == 0
 
The generic EFI stub can be instructed to avoid SetVirtualAddressMap(),
and simply run with the firmware's 1:1 mapping. In this case, it
populates the virtual address fields of the runtime regions in the
memory map with the physical address of each region, so that the mapping
code has to be none the wiser. Only if SetVirtualAddressMap() fails, the
virtual addresses are wiped and the kernel code knows that the regions
cannot be mapped.

However, wiping amounts to setting it to zero, and if a runtime region
happens to live at physical address 0, its valid 1:1 mapped virtual
address could be mistaken for a wiped field, resulting on loss of access
to the EFI services at runtime.

So let's only assume that VA == 0 means 'no runtime services' if the
region in question does not live at PA 0x0.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
1 parent 53a7ea2
History
Tip revision: 37926f96302d8b6c2bc97990d33e316a3ed6d67f authored by Ard Biesheuvel on 20 October 2022, 13:16:09 UTC
efi: runtime: Don't assume virtual mappings are missing if VA == PA == 0
Tip revision: 37926f9
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