On Fri, 4 Jul 2025 at 15:33, Will Deacon [off-list ref] wrote:

On Fri, Jul 04, 2025 at 01:36:40PM +0100, Breno Leitao wrote:

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On Fri, Jul 04, 2025 at 10:26:37AM +0200, Ard Biesheuvel wrote:

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On Thu, 3 Jul 2025 at 18:35, Catalin Marinas [off-list ref] wrote:

quoted

On Tue, Jun 24, 2025 at 05:55:53AM -0700, Breno Leitao wrote:

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 arch/arm64/kernel/efi.c | 9 ++++++---

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 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.

If VMAP_STACK is a hard requirement, should we make CONFIG_EFI depend
on it for arm64?

What about if we make CONFIG_EFI select VMAP_STACK? I think it is more
straight forward from a configuration perspective.

I thought about the following. What do you think?

      arm64: EFI selects VMAP_STACK

      Modify the ARM64 Kconfig to make the CONFIG_EFI configuration option
      automatically select CONFIG_VMAP_STACK.

      The motivation is that arm64_efi_rt_init() will fail at runtime if
      CONFIG_VMAP_STACK is not set, so the patch ensures that enabling EFI
      will always enable VMAP_STACK as well, and avoid having EFI disabled in
      case the user didn't set VMAP_STACK.

      Suggested-by: Ard Biesheuvel [off-list ref]
      Signed-off-by: Breno Leitao [off-list ref]

      diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
      index 55fc331af3371..cc2585143f511 100644
      --- a/arch/arm64/Kconfig
      +++ b/arch/arm64/Kconfig
      @@ -2437,6 +2437,7 @@ config EFI
              select EFI_RUNTIME_WRAPPERS
              select EFI_STUB
              select EFI_GENERIC_STUB
      +       select VMAP_STACK
              imply IMA_SECURE_AND_OR_TRUSTED_BOOT
              default y
              help

I would actually like to select VMAP_STACK unconditionally for arm64.
Historically, we were held back waiting for all the various KASAN modes
to support vmalloc properly, but I _think_ that's fixed now...

The VMAP_STACK dependency is:

        depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC

and in arm64 we have:

        select KASAN_VMALLOC if KASAN

so it should be fine to select it afaict.

I agree - we have plenty of vmalloc space, and the memory footprint is
the same so we should just turn this on unconditionally.