Re: [PATCH v10 12/50] x86/sev: Invalidate pages from the direct map when adding them to the RMP table

[Borislav Petkov]

On Mon, Oct 16, 2023 at 08:27:41AM -0500, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@xxxxxxx>
> 
> The integrity guarantee of SEV-SNP is enforced through the RMP table.
> The RMP is used with standard x86 and IOMMU page tables to enforce
> memory restrictions and page access rights. The RMP check is enforced as
> soon as SEV-SNP is enabled globally in the system. When hardware
> encounters an RMP-check failure, it raises a page-fault exception.
> 
> The rmp_make_private() and rmp_make_shared() helpers are used to add
> or remove the pages from the RMP table. Improve the rmp_make_private()
> to invalidate state so that pages cannot be used in the direct-map after
> they are added the RMP table, and restored to their default valid
> permission after the pages are removed from the RMP table.

Brijesh's SOB comes

<--- here,

then Ashish's two tags.

Please audit your whole set for such inconsistencies.

> @@ -404,6 +440,21 @@ static int rmpupdate(u64 pfn, struct rmp_state *val)
>  	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
>  		return -ENXIO;
>  
> +	level = RMP_TO_X86_PG_LEVEL(val->pagesize);
> +	npages = page_level_size(level) / PAGE_SIZE;
> +
> +	/*
> +	 * If page is getting assigned in the RMP table then unmap it from the
> +	 * direct map.

Here I'm missing the explanation *why* the pages need to be unmapped
from the direct map.

What happens if not?

> +	 */
> +	if (val->assigned) {
> +		if (invalidate_direct_map(pfn, npages)) {
> +			pr_err("Failed to unmap %d pages at pfn 0x%llx from the direct_map\n",
> +			       npages, pfn);

invalidate_direct_map() already dumps an error message - no need to do
that here too.

> +			return -EFAULT;
> +		}
> +	}
> +
>  	do {
>  		/* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
>  		asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
> @@ -422,6 +473,17 @@ static int rmpupdate(u64 pfn, struct rmp_state *val)
>  		return -EFAULT;
>  	}
>  
> +	/*
> +	 * Restore the direct map after the page is removed from the RMP table.
> +	 */
> +	if (!val->assigned) {
> +		if (restore_direct_map(pfn, npages)) {
> +			pr_err("Failed to map %d pages at pfn 0x%llx into the direct_map\n",
> +			       npages, pfn);

Ditto.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette