Le 21/08/2018 à 16:25, Aneesh Kumar K.V a écrit :

Christophe Leroy christophe.leroy@c-s.fr writes:

...

Commit 5769beaf180a8 ("powerpc/mm: Add proper pte access check helper for other platforms") replaced generic pte_access_permitted() by an arch specific one.

The generic one is defined as (pte_present(pte) && (!(write) || pte_write(pte)))

The arch specific one is open coded checking that _PAGE_USER and _PAGE_WRITE (_PAGE_RW) flags are set, but lacking to check that _PAGE_RO and _PAGE_PRIVILEGED are unset, leading to a useless test on targets like the 8xx which defines _PAGE_RW and _PAGE_USER as 0.

Commit 5fa5b16be5b31 ("powerpc/mm/hugetlb: Use pte_access_permitted for hugetlb access check") replaced some tests performed with pte helpers by a call to pte_access_permitted(), leading to the same issue.

This patch rewrites powerpc/nohash pte_access_permitted() using pte helpers.

Thanks for fixing this. I should have used the helper instead of opencoding it on nohash platforms. This is another reason why I was also suggesting we should avoid consolidating pte accessors across platforms and user accessors instead of opencoding.

I fully agree. I have opened a topic for that at https://github.com/linuxppc/linux/issues/177

Christophe

https://lore.kernel.org/lkml/87lgcusc6z.fsf@linux.vnet.ibm.com/T/#u

Reviewed-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com

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Fixes: 5769beaf180a8 ("powerpc/mm: Add proper pte access check helper for other platforms") Fixes: 5fa5b16be5b31 ("powerpc/mm/hugetlb: Use pte_access_permitted for hugetlb access check") Cc: stable@vger.kernel.org # v4.15+ Signed-off-by: Christophe Leroy christophe.leroy@c-s.fr

---

arch/powerpc/include/asm/nohash/pgtable.h | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h index 2160be2e4339..b321c82b3624 100644 --- a/arch/powerpc/include/asm/nohash/pgtable.h +++ b/arch/powerpc/include/asm/nohash/pgtable.h @@ -51,17 +51,14 @@ static inline int pte_present(pte_t pte) #define pte_access_permitted pte_access_permitted static inline bool pte_access_permitted(pte_t pte, bool write) {

• unsigned long pteval = pte_val(pte); /*
  • A read-only access is controlled by _PAGE_USER bit.
  • We have _PAGE_READ set for WRITE and EXECUTE
  */
• unsigned long need_pte_bits = _PAGE_PRESENT | _PAGE_USER;
• if (write)

• need_pte_bits |= _PAGE_WRITE;
  

• if (!pte_present(pte) || !pte_user(pte) || !pte_read(pte))

• return false;
  

• if ((pteval & need_pte_bits) != need_pte_bits)

• if (write && !pte_write(pte)) return false;

return true; -- 2.13.3