Re: [PATCH v9 5/7] poweprc: mm: Implement *_user_accessible_page() for ptes
From: Christophe Leroy <hidden>
Date: 2023-11-30 07:03:01
Le 30/11/2023 à 03:53, 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.
pte_access_permitted() returns false on an exec-only page.
As far as I can see in arm64, pte_user_accessible_page() returns true on
an exec-only page.
In addition, pte_access_permitted() is called only from GUP so is
garanteed to be called only for user pages. Do we have the same garantee
from callers of pte_user_accessible_page() ? If not it is needed to
check address in addition, see commit a78587473642 ("powerpc: Rely on
address instead of pte_user()")
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.pte_user() is not equivalent nor implies by pte_read(). In most platforms it is implied by the address being below TASK_SIZE. pte_read() will also return true on kernel readable pages.
quoted hunk ↗ jump to hunk
Signed-off-by: Rohan McLure <redacted> --- v9: New implementation --- arch/powerpc/include/asm/book3s/32/pgtable.h | 5 +++++ arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++++ arch/powerpc/include/asm/nohash/pgtable.h | 5 +++++ arch/powerpc/include/asm/pgtable.h | 15 +++++++++++++++ 4 files changed, 30 insertions(+)diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h index 9cc95a61d2a6..bd6f8cdd25aa 100644 --- a/arch/powerpc/include/asm/book3s/32/pgtable.h +++ b/arch/powerpc/include/asm/book3s/32/pgtable.h@@ -441,6 +441,11 @@ static inline bool pte_access_permitted(pte_t pte, bool write) return true; } +static inline bool pte_user_accessible_page(pte_t pte) +{ + return pte_present(pte) && pte_read(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. *diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h index 2454174b26cb..dd3e7b190ab7 100644 --- a/arch/powerpc/include/asm/book3s/64/pgtable.h +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h@@ -544,6 +544,11 @@ 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) +{ + return pte_present(pte) && pte_user(pte) && pte_read(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.diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h index 427db14292c9..33b4a4267f66 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) +{ + return pte_present(pte) && pte_read(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. *diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h index d7d0f47760d3..661bf3afca37 100644 --- a/arch/powerpc/include/asm/pgtable.h +++ b/arch/powerpc/include/asm/pgtable.h@@ -250,6 +250,21 @@ static inline pte_t pud_pte(pud_t pud) return __pte(pud_val(pud)); } #endif + +static inline bool pmd_user_accessible_page(pmd_t pmd) +{ + pte_t pte = pmd_pte(pmd); + + return pte_user_accessible_page(pte);
No need of that pte local var, can fit as a single line.
+}
+
+static inline bool pud_user_accessible_page(pud_t pud)
+{
+ pte_t pte = pud_pte(pud);
+
+ return pte_user_accessible_page(pte);Same.
+} + #endif /* __ASSEMBLY__ */ #endif /* _ASM_POWERPC_PGTABLE_H */