[PATCH v11 14/39] arm64/mm: Map pages for guarded control stack

Mark Brown
2024-08-22T01:18:57Z

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.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/include/asm/mman.h | 9 +++++++++
arch/arm64/mm/mmap.c | 10 +++++++++-
2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index c21849ffdd88..37dfd2882f04 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/arch/arm64/include/asm/mman.h
@@ -61,6 +61,15 @@ static inline bool arch_validate_flags(unsigned long vm_flags)
return false;
}

+ if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
+ /* An executable GCS isn't a good idea. */
+ if (vm_flags & VM_EXEC)
+ return false;
+
+ /* The memory management core should prevent this */
+ VM_WARN_ON(vm_flags & VM_SHARED);
+ }
+
return true;

}
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 642bdf908b22..3ed63fc8cd0a 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -83,9 +83,17 @@ 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;
+
+ /* Short circuit GCS to avoid bloating the table. */
+ if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {
+ prot = _PAGE_GCS_RO;
+ } else {
+ prot = pgprot_val(protection_map[vm_flags &
(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);
+ }

+ /* VM_ARM64_BTI on a GCS is rejected in arch_validate_flags() */
if (vm_flags & VM_ARM64_BTI)
prot |= PTE_GP;

--
2.39.2