Re: [PATCH v11 09/11] poweprc: mm: Implement *_user_accessible_page() for ptes

Christophe Leroy
2024-03-28T05:41:08Z

Le 28/03/2024 à 05:55, Rohan McLure a écrit :
> Page table checking depends on architectures providing an
> implementation of p{te,md,ud}_user_accessible_page. With
> refactorisations made on powerpc/mm, the pte_access_permitted() and
> similar methods verify whether a userland page is accessible with the
> required permissions.
>
> Since page table checking is the only user of
> p{te,md,ud}_user_accessible_page(), implement these for all platforms,
> using some of the same preliminary checks taken by pte_access_permitted()
> on that platform.
>
> Since Commit 8e9bd41e4ce1 ("powerpc/nohash: Replace pte_user() by pte_read()")
> pte_user() is no longer required to be present on all platforms as it
> may be equivalent to or implied by pte_read(). Hence implementations of
> pte_user_accessible_page() are specialised.
>
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> ---
> v9: New implementation
> v10: Let book3s/64 use pte_user(), but otherwise default other platforms
> to using the address provided with the call to infer whether it is a
> user page or not. pmd/pud variants will warn on all other platforms, as
> they should not be used for user page mappings
> v11: Conditionally define p{m,u}d_user_accessible_page(), as not all
> platforms have p{m,u}d_leaf(), p{m,u}d_pte() stubs.

See my comment to v10 patch 10.

p{m,u}d_leaf() is defined for all platforms (There is a fallback
definition in include/linux/pgtable.h) so p{m,u}d_user_accessible_page()
can be defined for all platforms, no need for a conditionally define.

> ---
> arch/powerpc/include/asm/book3s/32/pgtable.h | 5 +++++
> arch/powerpc/include/asm/book3s/64/pgtable.h | 17 +++++++++++++++++
> arch/powerpc/include/asm/nohash/pgtable.h | 5 +++++
> arch/powerpc/include/asm/pgtable.h | 8 ++++++++
> 4 files changed, 35 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
> index 52971ee30717..83f7b98ef49f 100644
> --- a/arch/powerpc/include/asm/book3s/32/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
> @@ -436,6 +436,11 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
> return true;
> }
>
> +static inline bool pte_user_accessible_page(pte_t pte, unsigned long addr)
> +{
> + return pte_present(pte) && !is_kernel_addr(addr);
> +}
> +
> /* Conversion functions: convert a page and protection to a page entry,
> * and a page entry and page directory to the page they refer to.
> *
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index fac5615e6bc5..d8640ddbcad1 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -538,6 +538,11 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
> return arch_pte_access_permitted(pte_val(pte), write, 0);
> }
>
> +static inline bool pte_user_accessible_page(pte_t pte, unsigned long addr)
> +{
> + return pte_present(pte) && pte_user(pte);
> +}
> +
> /*
> * Conversion functions: convert a page and protection to a page entry,
> * and a page entry and page directory to the page they refer to.
> @@ -1441,5 +1446,17 @@ static inline bool pud_leaf(pud_t pud)
> return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PTE));
> }
>
> +#define pmd_user_accessible_page pmd_user_accessible_page
> +static inline bool pmd_user_accessible_page(pmd_t pmd, unsigned long addr)
> +{
> + return pmd_leaf(pmd) && pte_user_accessible_page(pmd_pte(pmd), addr);
> +}
> +
> +#define pud_user_accessible_page pud_user_accessible_page
> +static inline bool pud_user_accessible_page(pud_t pud, unsigned long addr)
> +{
> + return pud_leaf(pud) && pte_user_accessible_page(pud_pte(pud), addr);
> +}
> +
> #endif /* __ASSEMBLY__ */
> #endif /* _ASM_POWERPC_BOOK3S_64_PGTABLE_H_ */
> diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
> index 427db14292c9..413d01a51e6f 100644
> --- a/arch/powerpc/include/asm/nohash/pgtable.h
> +++ b/arch/powerpc/include/asm/nohash/pgtable.h
> @@ -213,6 +213,11 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
> return true;
> }
>
> +static inline bool pte_user_accessible_page(pte_t pte, unsigned long addr)
> +{
> + return pte_present(pte) && !is_kernel_addr(addr);
> +}
> +
> /* Conversion functions: convert a page and protection to a page entry,
> * and a page entry and page directory to the page they refer to.
> *
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index ee8c82c0528f..f1ceae778cb1 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -219,6 +219,14 @@ static inline int pud_pfn(pud_t pud)
> }
> #endif
>
> +#ifndef pmd_user_accessible_page
> +#define pmd_user_accessible_page(pmd, addr) false
> +#endif
> +
> +#ifndef pud_user_accessible_page
> +#define pud_user_accessible_page(pud, addr) false
> +#endif
> +
> #endif /* __ASSEMBLY__ */
>
> #endif /* _ASM_POWERPC_PGTABLE_H */