Re: [PATCH] x86/sev: Apply RMP table fixups for kexec.

Tom Lendacky <thomas.lendacky@xxxxxxx> · Tue, 2 Apr 2024 10:54:50 -0500

On 4/2/24 09:45, bp@xxxxxxxxxx wrote:

From: Borislav Petkov <bp@xxxxxxxxx>

On Tue, Mar 12, 2024 at 06:47:57PM +0000, Ashish Kalra wrote:

From: Ashish Kalra <ashish.kalra@xxxxxxx>

RMP table start and end physical range may not be aligned to 2MB in
the e820 tables

This already sounds fishy. Why may the range not be aligned? This is
BIOS, right? And BIOS can be fixed to align them properly.

There's no requirement from a hardware/RMP usage perspective that 

requires a 2MB alignment, so BIOS is not doing anything wrong. The 

problem occurs because kexec is initially using 2MB mappings that 

overlap the start and/or end of the RMP which then results in an RMP 

fault when memory within one of those 2MB mappings, that is not part of 

the RMP, is referenced.

Additionally, we have BIOSes out there since Milan that don't do this 

2MB alignment. And do you really trust that BIOS will do this properly 

all the time?

I think it needs to be checked and mitigated in the kernel.

Thanks,
Tom