[PATCH 12/35] arm64/mm: Map pages for guarded control stack

[Mark Brown]

Map pages flagged as being part of a GCS as such rather than using the
full set of generic VM flags.

This is done using a conditional rather than extending the size of
protection_map since that would make for a very sparse array.

Signed-off-by: Mark Brown <broonie at kernel.org>
---
 arch/arm64/mm/mmap.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 8f5b7ce857ed..e2ca770920ed 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -79,8 +79,23 @@ arch_initcall(adjust_protection_map);
 
 pgprot_t vm_get_page_prot(unsigned long vm_flags)
 {
-	pteval_t prot = pgprot_val(protection_map[vm_flags &
+	pteval_t prot;
+
+	/*
+	 * If this is a GCS then only interpret VM_WRITE.
+	 *
+	 * TODO: Just make protection_map[] bigger?  Nothing seems
+	 * ideal here.
+	 */
+	if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
+		if (vm_flags & VM_WRITE)
+			prot = _PAGE_GCS;
+		else
+			prot = _PAGE_GCS_RO;
+	} else {
+		prot = pgprot_val(protection_map[vm_flags &
 				   (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);
+	}
 
 	if (vm_flags & VM_ARM64_BTI)
 		prot |= PTE_GP;

-- 
2.30.2