[RFC PATCH 4/5] X86:Prevent write to read-only pages :text, PLT/GOT tables from another process

[Lev Olshvang <levonshe@gmail.com>]

Signed-off-by: Lev Olshvang <levonshe@gmail.com>
---
 arch/x86/include/asm/mmu_context.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 4e55370e48e8..708135112d95 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -216,12 +216,19 @@ static inline void arch_unmap(struct mm_struct *mm, unsigned long start,
 static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 		bool write, bool execute, bool foreign)
 {
-	/* pkeys never affect instruction fetches */
+#ifdef CONFIG_PROTECT_READONLY_USER_MEMORY
+	/* Forbid write to PROT_READ pages of foreign process */
+	if (write && foreign && (!(vma->vm_flags & VM_WRITE)))
+		return false;
+#endif
+	/* Don't check PKRU since pkeys never affect instruction fetches */
 	if (execute)
 		return true;
+
 	/* allow access if the VMA is not one from this process */
 	if (foreign || vma_is_foreign(vma))
 		return true;
+
 	return __pkru_allows_pkey(vma_pkey(vma), write);
 }

--
2.17.1