ARM: 8235/1: Support for the PXN CPU feature on ARMv7

Modern ARMv7-A/R cores optionally implement below new
hardware feature:

- PXN:
Privileged execute-never(PXN) is a security feature. PXN bit
determines whether the processor can execute software from
the region. This is effective solution against ret2usr attack.
On an implementation that does not include the LPAE, PXN is
optionally supported.

This patch set PXN bit on user page table for preventing
user code execution with privilege mode.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Jungseung Lee <js07.lee@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 9 insertions, 1 deletions

diff --git a/arch/arm/include/asm/pgalloc.h b/arch/arm/include/asm/pgalloc.h
index 78a779361682..19cfab526d13 100644
--- a/arch/arm/include/asm/pgalloc.h
+++ b/arch/arm/include/asm/pgalloc.h
@@ -157,7 +157,15 @@ pmd_populate_kernel(struct mm_struct *mm, pmd_t *pmdp, pte_t *ptep)
 static inline void
 pmd_populate(struct mm_struct *mm, pmd_t *pmdp, pgtable_t ptep)
 {
-	__pmd_populate(pmdp, page_to_phys(ptep), _PAGE_USER_TABLE);
+	extern pmdval_t user_pmd_table;
+	pmdval_t prot;
+
+	if (__LINUX_ARM_ARCH__ >= 6 && !IS_ENABLED(CONFIG_ARM_LPAE))
+		prot = user_pmd_table;
+	else
+		prot = _PAGE_USER_TABLE;
+
+	__pmd_populate(pmdp, page_to_phys(ptep), prot);
 }
 #define pmd_pgtable(pmd) pmd_page(pmd)