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@xxxxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
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..6d3fe6433a62 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, and the mm
+ * core can't cope with a shared GCS.
+ */
+ if (vm_flags & (VM_EXEC | VM_ARM64_BTI | VM_SHARED))
+ return false;
+ }
+
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
