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Subject[PATCH 4.9 013/138] arm64: Implement arch-specific pte_access_permitted()
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Catalin Marinas <catalin.marinas@arm.com>

commit 6218f96c58dbf44a06aeaf767aab1f54fc397838 upstream.

The generic pte_access_permitted() implementation only checks for
pte_present() (together with the write permission where applicable).
However, for both kernel ptes and PROT_NONE mappings pte_present() also
returns true on arm64 even though such mappings are not user accessible.
Additionally, arm64 now supports execute-only user permission
(PROT_EXEC) which is implemented by clearing the PTE_USER bit.

With this patch the arm64 implementation of pte_access_permitted()
checks for the PTE_VALID and PTE_USER bits together with writable access
if applicable.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/include/asm/pgtable.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)

--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -91,6 +91,8 @@ extern unsigned long empty_zero_page[PAG
((pte_val(pte) & (PTE_VALID | PTE_USER | PTE_UXN)) == (PTE_VALID | PTE_UXN))
#define pte_valid_young(pte) \
((pte_val(pte) & (PTE_VALID | PTE_AF)) == (PTE_VALID | PTE_AF))
+#define pte_valid_user(pte) \
+ ((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER))

/*
* Could the pte be present in the TLB? We must check mm_tlb_flush_pending
@@ -100,6 +102,18 @@ extern unsigned long empty_zero_page[PAG
#define pte_accessible(mm, pte) \
(mm_tlb_flush_pending(mm) ? pte_present(pte) : pte_valid_young(pte))

+/*
+ * p??_access_permitted() is true for valid user mappings (subject to the
+ * write permission check) other than user execute-only which do not have the
+ * PTE_USER bit set. PROT_NONE mappings do not have the PTE_VALID bit set.
+ */
+#define pte_access_permitted(pte, write) \
+ (pte_valid_user(pte) && (!(write) || pte_write(pte)))
+#define pmd_access_permitted(pmd, write) \
+ (pte_access_permitted(pmd_pte(pmd), (write)))
+#define pud_access_permitted(pud, write) \
+ (pte_access_permitted(pud_pte(pud), (write)))
+
static inline pte_t clear_pte_bit(pte_t pte, pgprot_t prot)
{
pte_val(pte) &= ~pgprot_val(prot);

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