Re: [PATCH v7 14/45] x86/compressed: Add helper for validating pages in the decompression stage

Borislav Petkov
2021-12-07T11:48:07Z

On Wed, Nov 10, 2021 at 04:07:00PM -0600, Brijesh Singh wrote:
> diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
> index f7213d0943b8..3cf7a7575f5c 100644
> --- a/arch/x86/boot/compressed/ident_map_64.c
> +++ b/arch/x86/boot/compressed/ident_map_64.c
> @@ -275,15 +275,31 @@ static int set_clr_page_flags(struct x86_mapping_info *info,
> * Changing encryption attributes of a page requires to flush it from
> * the caches.
> */
> - if ((set | clr) & _PAGE_ENC)
> + if ((set | clr) & _PAGE_ENC) {
> clflush_page(address);
>
> + /*
> + * If the encryption attribute is being cleared, then change
> + * the page state to shared in the RMP table.
> + */
> + if (clr)
> + snp_set_page_shared(pte_pfn(*ptep) << PAGE_SHIFT);

So I'm wondering: __page_state_change() wants a physical address and
you're reading it out from the PTE here.

Why not do

__pa(address & PAGE_MASK);

like it is usually done?

And those macros are right there at the top of ident_map_64.c with an
explanation that we're ident-mapped here so pa == va...

> + }
> +
> /* Update PTE */
> pte = *ptep;
> pte = pte_set_flags(pte, set);
> pte = pte_clear_flags(pte, clr);
> set_pte(ptep, pte);
>
> + /*
> + * If the encryption attribute is being set, then change the page state to
> + * private in the RMP entry. The page state must be done after the PTE
^
change

> + * is updated.
> + */
> + if (set & _PAGE_ENC)
> + snp_set_page_private(pte_pfn(*ptep) << PAGE_SHIFT);
> +
> /* Flush TLB after changing encryption attribute */
> write_cr3(top_level_pgt);
>
--
Regards/Gruss,
Boris.