Re: [PATCH 1/5] x86/tboot: drop failed attempt to hash shadow page tables

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.12.2022 14:53, Jan Beulich wrote:
> While plausible to do what was intended based on the name of the flag
> (PGC_page_table), that name was misleading and is going to be changed.
> It marks page tables pages _having_ a shadow, not shadows of page table
> pages. The attempt also didn't cover the HAP case at all, and it
> constituted a potentially very long loop doing nothing when
> !SHADOW_PAGING. Instead leave a comment of what actually wants doing
> there (which then also may need to account for e.g. the risk of A/D bits
> becoming set behind our backs).
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I'm sorry, I should have Cc-ed tboot reviewers here as well.

Jan

> --- a/xen/arch/x86/tboot.c
> +++ b/xen/arch/x86/tboot.c
> @@ -177,29 +177,6 @@ static void update_iommu_mac(vmac_ctx_t
>  #define is_page_in_use(page) \
>      (page_state_is(page, inuse) || page_state_is(page, offlining))
>  
> -static void update_pagetable_mac(vmac_ctx_t *ctx)
> -{
> -    unsigned long mfn;
> -
> -    for ( mfn = 0; mfn < max_page; mfn++ )
> -    {
> -        struct page_info *page = mfn_to_page(_mfn(mfn));
> -
> -        if ( !mfn_valid(_mfn(mfn)) )
> -            continue;
> -        if ( is_page_in_use(page) && !is_special_page(page) )
> -        {
> -            if ( page->count_info & PGC_page_table )
> -            {
> -                void *pg = map_domain_page(_mfn(mfn));
> -
> -                vmac_update(pg, PAGE_SIZE, ctx);
> -                unmap_domain_page(pg);
> -            }
> -        }
> -    }
> -}
> - 
>  static void tboot_gen_domain_integrity(const uint8_t key[TB_KEY_SIZE],
>                                         vmac_t *mac)
>  {
> @@ -233,8 +210,7 @@ static void tboot_gen_domain_integrity(c
>          }
>      }
>  
> -    /* MAC all shadow page tables */
> -    update_pagetable_mac(&ctx);
> +    /* TODO: MAC all shadow / HAP page tables */
>  
>      *mac = vmac(NULL, 0, nonce, NULL, &ctx);
>  
> 
>