Re: [RFC Part1 PATCH 11/13] x86/kernel: validate rom memory before accessing when SEV-SNP is active

Brijesh Singh
2021-04-09T17:40:55Z

On 4/9/21 11:53 AM, Borislav Petkov wrote:
> On Wed, Mar 24, 2021 at 11:44:22AM -0500, Brijesh Singh wrote:
>> + /*
>> + * The ROM memory is not part of the E820 system RAM and is not prevalidated by the BIOS.
>> + * The kernel page table maps the ROM region as encrypted memory, the SEV-SNP requires
>> + * the all the encrypted memory must be validated before the access.
>> + */
>> + if (sev_snp_active()) {
>> + unsigned long n, paddr;
>> +
>> + n = ((system_rom_resource.end + 1) - video_rom_resource.start) >> PAGE_SHIFT;
>> + paddr = video_rom_resource.start;
>> + early_snp_set_memory_private((unsigned long)__va(paddr), paddr, n);
>> + }
> I don't like this sprinkling of SNP-special stuff that needs to be done,
> around the tree. Instead, pls define a function called
>
> snp_prep_memory(unsigned long pa, unsigned int num_pages, enum operation);
>
> or so which does all the manipulation needed and the callsites only
> simply unconditionally call that function so that all detail is
> extracted and optimized away when not config-enabled.

Sure, I will do this in the next rev.

>
> Thx.
>