[PATCH v2] arm64: efi: Fix KASAN false positive for EFI runtime stack

[Breno Leitao]

KASAN reports invalid accesses during arch_stack_walk() for EFI runtime
services due to vmalloc tagging[1]. The EFI runtime stack must be allocated
with KASAN tags reset to avoid false positives.

This patch uses arch_alloc_vmap_stack() instead of __vmalloc_node() for
EFI stack allocation, which internally calls kasan_reset_tag()

The changes ensure EFI runtime stacks are properly sanitized for KASAN
while maintaining functional consistency.

Link: https://lore.kernel.org/all/aFVVEgD0236LdrL6@gmail.com/ [1]
Suggested-by: Andrey Konovalov <andreyknvl at gmail.com>
Suggested-by: Catalin Marinas <catalin.marinas at arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Breno Leitao <leitao at debian.org>
---
Changes in v2:
- Clear the EFI_RUNTIME_SERVICES in efi.flags before returning (Mark/Catalin)
- Link to v1: https://lore.kernel.org/r/20250624-arm_kasan-v1-1-21e80eab3d70@debian.org
---
 arch/arm64/kernel/efi.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index 3857fd7ee8d46..62230d6dd919c 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -15,6 +15,7 @@
 
 #include <asm/efi.h>
 #include <asm/stacktrace.h>
+#include <asm/vmap_stack.h>
 
 static bool region_is_misaligned(const efi_memory_desc_t *md)
 {
@@ -214,9 +215,13 @@ static int __init arm64_efi_rt_init(void)
 	if (!efi_enabled(EFI_RUNTIME_SERVICES))
 		return 0;
 
-	p = __vmalloc_node(THREAD_SIZE, THREAD_ALIGN, GFP_KERNEL,
-			   NUMA_NO_NODE, &&l);
-l:	if (!p) {
+	if (!IS_ENABLED(CONFIG_VMAP_STACK)) {
+		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
+		return -ENOMEM;
+	}
+
+	p = arch_alloc_vmap_stack(THREAD_SIZE, NUMA_NO_NODE);
+	if (!p) {
 		pr_warn("Failed to allocate EFI runtime stack\n");
 		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
 		return -ENOMEM;

---
base-commit: 6b9fd8857b9fc4dd62e7cd300327f0e48dd76642
change-id: 20250623-arm_kasan-3b1d120ec20f

Best regards,
--  
Breno Leitao <leitao at debian.org>