Re: [PATCH v9 18/43] x86/kernel: Validate ROM memory before accessing when SEV-SNP is active

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On Fri, Jan 28, 2022 at 11:17:39AM -0600, Brijesh Singh wrote:
> @@ -197,11 +198,21 @@ static int __init romchecksum(const unsigned char *rom, unsigned long length)
>  
>  void __init probe_roms(void)
>  {
> -	const unsigned char *rom;
>  	unsigned long start, length, upper;
> +	const unsigned char *rom;
>  	unsigned char c;
>  	int i;
>  
> +	/*
> +	 * The ROM memory is not part of the E820 system RAM and is not pre-validated
> +	 * by the BIOS. The kernel page table maps the ROM region as encrypted memory,
> +	 * the SEV-SNP requires the encrypted memory must be validated before the
> +	 * access. Validate the ROM before accessing it.
> +	 */

Lemme massage it:

        /*
         * The ROM memory range is not part of the e820 table and is therefore not
         * pre-validated by BIOS. The kernel page table maps the ROM region as encrypted
         * memory, and SEV-SNP requires encrypted memory to be validated before access.
         * Do that here.
         */

-- 
Regards/Gruss,
    Boris.

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