arm64/mm: Map pages for guarded control stack

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>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241001-arm64-gcs-v13-15-222b78d87eee@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index 03b790fd0ad803e12f647f90a03c461916596398..f6d784f8e6e04ffb738f8611b2f5ad6c5dfde4e5 100644 (file)
--- a/arch/arm64/include/asm/mman.h
+++ b/arch/arm64/include/asm/mman.h
@@ -71,6 +71,15 @@ 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 7e3ad97e27d80ded18f4688376358433942e81e0..07aeab8a760652efa3dcaeb154ea73c6a2185069 100644 (file)
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -83,8 +83,15 @@ 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)]);
+       }
 
        if (vm_flags & VM_ARM64_BTI)
                prot |= PTE_GP;