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

[Catalin Marinas]

On Tue, Jun 24, 2025 at 05:55:53AM -0700, Breno Leitao wrote:
> 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>
> Signed-off-by: Breno Leitao <leitao at debian.org>
> ---
>  arch/arm64/kernel/efi.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> index 3857fd7ee8d46..d2af881a48290 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 +215,11 @@ 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))
> +		return -ENOMEM;

Mark Rutland pointed out in a private chat that this should probably
clear the EFI_RUNTIME_SERVICES flag as well.

> +
> +	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;
> 

With that:

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>

(but let's see if Ard has a different opinion on the approach)