Re: [PATCH v10 10/12] poweprc: mm: Implement *_user_accessible_page() for ptes

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 13/03/2024 à 05:21, 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 preliminay 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 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
> ---
>   arch/powerpc/include/asm/book3s/64/pgtable.h | 19 ++++++++++++++
>   arch/powerpc/include/asm/pgtable.h           | 26 ++++++++++++++++++++
>   2 files changed, 45 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 382724c5e872..ca765331e21d 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -538,6 +538,12 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
>   	return arch_pte_access_permitted(pte_val(pte), write, 0);
>   }
>   
> +#define pte_user_accessible_page pte_user_accessible_page
> +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.
> @@ -881,6 +887,7 @@ static inline int pud_present(pud_t pud)
>   
>   extern struct page *pud_page(pud_t pud);
>   extern struct page *pmd_page(pmd_t pmd);
> +

Garbage ?

>   static inline pte_t pud_pte(pud_t pud)
>   {
>   	return __pte_raw(pud_raw(pud));
> @@ -926,6 +933,12 @@ static inline bool pud_access_permitted(pud_t pud, bool write)
>   	return pte_access_permitted(pud_pte(pud), write);
>   }
>   
> +#define pud_user_accessible_page pud_user_accessible_page
> +static inline bool pud_user_accessible_page(pud_t pud, unsigned long addr)
> +{
> +	return pte_user_accessible_page(pud_pte(pud), addr);
> +}
> +

If I understand what is done on arm64, you should first check 
pud_leaf(). Then this function could be common to all powerpc platforms, 
only pte_user_accessible_page() would be platform specific.

>   #define __p4d_raw(x)	((p4d_t) { __pgd_raw(x) })
>   static inline __be64 p4d_raw(p4d_t x)
>   {
> @@ -1091,6 +1104,12 @@ static inline bool pmd_access_permitted(pmd_t pmd, bool write)
>   	return pte_access_permitted(pmd_pte(pmd), write);
>   }
>   
> +#define pmd_user_accessible_page pmd_user_accessible_page
> +static inline bool pmd_user_accessible_page(pmd_t pmd, unsigned long addr)
> +{
> +	return pte_user_accessible_page(pmd_pte(pmd), addr);
> +}

Same, pmd_leaf() should be checked.

> +
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>   extern pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot);
>   extern pud_t pfn_pud(unsigned long pfn, pgprot_t pgprot);
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index 13f661831333..3741a63fb82e 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -227,6 +227,32 @@ static inline int pud_pfn(pud_t pud)
>   }
>   #endif
>   
> +#ifndef pte_user_accessible_page
> +#define pte_user_accessible_page pte_user_accessible_page
> +static inline bool pte_user_accessible_page(pte_t pte, unsigned long addr)
> +{
> +	return pte_present(pte) && !is_kernel_addr(addr);
> +}
> +#endif

I would prefer to see one version in asm/book3s/32/pgtable.h and one in 
asm/nohash/pgtable.h and then avoid this game with ifdefs.

> +
> +#ifndef pmd_user_accessible_page
> +#define pmd_user_accessible_page pmd_user_accessible_page
> +static inline bool pmd_user_accessible_page(pmd_t pmd, unsigned long addr)
> +{
> +	WARN_ONCE(1, "pmd: platform does not use pmd entries directly");
> +	return false;
> +}
> +#endif

Also check pmd_leaf() and this function on all platforms.

> +
> +#ifndef pud_user_accessible_page
> +#define pud_user_accessible_page pud_user_accessible_page
> +static inline bool pud_user_accessible_page(pud_t pud, unsigned long addr)
> +{
> +	WARN_ONCE(1, "pud: platform does not use pud entries directly");
> +	return false;
> +}

Also check pud_leaf() and this function on all platforms.

> +#endif
> +
>   #endif /* __ASSEMBLY__ */
>   
>   #endif /* _ASM_POWERPC_PGTABLE_H */
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