From 47a8aad135ac1aed04b7b0c0a8157fd208075827 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Mon, 23 Feb 2026 17:45:31 +0000 Subject: [PATCH] arm64: gcs: Honour mprotect(PROT_NONE) on shadow stack mappings vm_get_page_prot() short-circuits the protection_map[] lookup for a VM_SHADOW_STACK mapping since it uses a different PIE index from the typical read/write/exec permissions. However, the side effect is that it also ignores mprotect(PROT_NONE) by creating an accessible PTE. Special-case the !(vm_flags & VM_ACCESS_FLAGS) flags to use the protection_map[VM_NONE] permissions instead. No GCS attributes are required for an inaccessible PTE. Signed-off-by: Catalin Marinas Fixes: 6497b66ba694 ("arm64/mm: Map pages for guarded control stack") Cc: stable@vger.kernel.org Cc: Mark Brown Cc: Will Deacon Cc: David Hildenbrand Reviewed-by: David Hildenbrand (Arm) Signed-off-by: Will Deacon --- arch/arm64/mm/mmap.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c index 75f343009b4b..92b2f5097a96 100644 --- a/arch/arm64/mm/mmap.c +++ b/arch/arm64/mm/mmap.c @@ -91,7 +91,11 @@ pgprot_t vm_get_page_prot(vm_flags_t vm_flags) /* Short circuit GCS to avoid bloating the table. */ if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) { - prot = gcs_page_prot; + /* Honour mprotect(PROT_NONE) on shadow stack mappings */ + if (vm_flags & VM_ACCESS_FLAGS) + prot = gcs_page_prot; + else + prot = pgprot_val(protection_map[VM_NONE]); } else { prot = pgprot_val(protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);