Le 12/09/2022 à 03:47, Rohan McLure a écrit :
> Add the following helpers for detecting whether a page table entry
> is a leaf and is accessible to user space.
>
> * pte_user_accessible_page
> * pmd_user_accessible_page
> * pud_user_accessible_page
>
> The heavy lifting is done by pte_user, which checks user accessibility
> on a per-mmu level, provided prior to this commit.
>
> On 32-bit systems, provide stub implementations for these methods, with
> BUG(), as debug features such as page table checks will emit functions
> that call p{md,ud}_user_accessible_page but must not be used.
Why "must not be used" ?
>
> Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com>
> ---
> arch/powerpc/include/asm/pgtable.h | 35 ++++++++++++++++++++++++++++
> 1 file changed, 35 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/pgtable.h
> b/arch/powerpc/include/asm/pgtable.h
> index 522145b16a07..8c1f5feb9360 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -170,6 +170,41 @@ static inline int pud_pfn(pud_t pud)
> return 0;
> }
>
> +static inline bool pte_user_accessible_page(pte_t pte)
> +{
> + return (pte_val(pte) & _PAGE_PRESENT) && pte_user(pte);
Should use pte_present() instead ?
> +}
> +
> +#ifdef CONFIG_PPC64
I think the functions could be valid for PPC32 as well with below changes:
> +
> +static inline bool pmd_user_accessible_page(pmd_t pmd)
> +{
> + return pmd_is_leaf(pmd) && pmd_present(pmd)
> + && pte_user(pmd_pte(pmd));
Define and use pmd_user()
> +}
> +
> +static inline bool pud_user_accessible_page(pud_t pud)
> +{
> + return pud_is_leaf(pud) && pud_present(pud)
> + && pte_user(pud_pte(pud));
Use pud_user().
For ppc64 you have to define it in
arch/powerpc/include/asm/book3s/64/pgtable.h and
arch/powerpc/include/asm/nohash/64/pgtable.h
For ppc32 it is already defined in include/asm-generic/pgtable-nopmd.h
And use pud_leaf() instead of pud_is_leaf(). For ppc32 it is already
defined in include/asm-generic/pgtable-nopmd.h
> +}
> +
> +#else
> +
> +static inline bool pmd_user_accessible_page(pmd_t pmd)
> +{
> + BUG();
> + return false;
> +}
> +
> +static inline bool pud_user_accessible_page(pud_t pud)
> +{
> + BUG();
> + return false;
> +}
> +
> +#endif /* CONFIG_PPC64 */
> +
> #endif /* __ASSEMBLY__ */
>
> #endif /* _ASM_POWERPC_PGTABLE_H */
