Re: Linux 6.11-rc1

[Guenter Roeck]

On 7/31/24 09:31, Peter Zijlstra wrote:
> On Wed, Jul 31, 2024 at 09:17:44AM -0700, Linus Torvalds wrote:
> > On Wed, 31 Jul 2024 at 08:55, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > > Right, so Thomas found that i386-pti fails to map the entire entry text.
> > > Specifically pti_clone_pgtable() hard relies -- and does not verify --
> > > that the start address is aligned to the given granularity.
> > >
> > > Now, i386 does not align __entry_text_start, and so the termination
> > > condition goes sideways and pte_clone_entry() does not always work right
> > > and it becomes a games of code layout roulette.
> >
> > Lovely.
>
> :-)
>
> This fixes the alignment assumptions and makes it all go again.

Confirmed.

Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

Thanks,
Guenter

> diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
> index 2e69abf4f852..bfdf5f45b137 100644
> --- a/arch/x86/mm/pti.c
> +++ b/arch/x86/mm/pti.c
> @@ -374,14 +374,14 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
>   			 */
>   			*target_pmd = *pmd;
>   
> -			addr += PMD_SIZE;
> +			addr = round_up(addr + 1, PMD_SIZE);
>   
>   		} else if (level == PTI_CLONE_PTE) {
>   
>   			/* Walk the page-table down to the pte level */
>   			pte = pte_offset_kernel(pmd, addr);
>   			if (pte_none(*pte)) {
> -				addr += PAGE_SIZE;
> +				addr = round_up(addr + 1, PAGE_SIZE);
>   				continue;
>   			}
>   
> @@ -401,7 +401,7 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
>   			/* Clone the PTE */
>   			*target_pte = *pte;
>   
> -			addr += PAGE_SIZE;
> +			addr = round_up(addr + 1, PAGE_SIZE);
>   
>   		} else {
>   			BUG();