[PATCH v4 11/36] arm64/mm: Map pages for guarded control stack

Mark Brown
2023-08-07T22:02:51Z

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@kernel.org>
---
arch/arm64/mm/mmap.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 8f5b7ce857ed..8f40198cd44e 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -79,8 +79,18 @@ 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. */
+ 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