linux-kernel - Re: [PATCH] x86/efi: Apply EFI Memory Attributes after kexec

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Message-ID: <CAMj1kXH2FRxwryJ9kz4CThWG_D30nW6g-UJzxW9uRQzBAZEetA@mail.gmail.com>
Date: Tue, 12 Nov 2024 08:55:51 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Nicolas Saenz Julienne <nsaenz@...zon.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H . Peter Anvin" <hpa@...or.com>, Sai Praneeth <sai.praneeth.prakhya@...el.com>, 
	Matt Fleming <matt@...eblueprint.co.uk>, linux-efi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stanspas@...zon.de, nh-open-source@...zon.com, 
	stable@...r.kernel.org
Subject: Re: [PATCH] x86/efi: Apply EFI Memory Attributes after kexec

On Mon, 11 Nov 2024 at 22:45, Nicolas Saenz Julienne <nsaenz@...zon.com> wrote:
>
> Kexec bypasses EFI's switch to virtual mode. In exchange, it has its own
> routine, kexec_enter_virtual_mode(), that replays the mappings made by
> the original kernel. Unfortunately, the function fails to reinstate
> EFI's memory attributes and runtime memory protections, which would've
> otherwise been set after entering virtual mode. Remediate this by
> calling efi_runtime_update_mappings() from it.
>
> Cc: stable@...r.kernel.org
> Fixes: 18141e89a76c ("x86/efi: Add support for EFI_MEMORY_ATTRIBUTES_TABLE")
> Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
>
> ---
>
> Notes:
> - I tested the Memory Attributes path using QEMU/OVMF.
>
> - Although care is taken to make sure the memory backing the EFI Memory
>   Attributes table is preserved during runtime and reachable after kexec
>   (see efi_memattr_init()). I don't see the same happening for the EFI
>   properties table. Maybe it's just unnecessary as there's an assumption
>   that the table will fall in memory preserved during runtime? Or for
>   another reason? Otherwise, we'd need to make sure it isn't possible to
>   set EFI_NX_PE_DATA on kexec.
>
>  arch/x86/platform/efi/efi.c | 1 +
>  1 file changed, 1 insertion(+)
>

Thanks.

I think we should just drop support for the EFI_PROPERTIES_TABLE - it
was a failed, short-lived experiment that broke the boot on both Linux
and Windows, and was replaced with the memory attributes table shortly
after.


> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> index 88a96816de9a..b9b17892c495 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -784,6 +784,7 @@ static void __init kexec_enter_virtual_mode(void)
>
>         efi_sync_low_kernel_mappings();
>         efi_native_runtime_setup();
> +       efi_runtime_update_mappings();
>  #endif
>  }
>
> --
> 2.40.1
>