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

On Thu, 2024-03-28 at 05:40 +0000, Christophe Leroy wrote:

Le 28/03/2024 à 05:55, Rohan McLure a écrit :

quoted

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 <redacted>
---
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.

The issue I see is that the definition in include/linux/pgtable.h
occurs after this header is included. Prior to the removal of a local
definition of p{m,u}d_leaf() etc we didn't run into this issue, but we
still do now.

Not insistent on doing it this way with ifndef, so amenable to
suggestions if you have a preference.

quoted

---
  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 */