linux-kernel - Re: [PATCH] x86/efi: Free EFI memory map only when installing a new one.

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Date: Wed, 12 Jun 2024 18:36:56 +0800
From: Dave Young <dyoung@...hat.com>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>, Ashish Kalra <Ashish.Kalra@....com>, Mike Rapoport <rppt@...nel.org>, 
	Borislav Petkov <bp@...en8.de>, Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH] x86/efi: Free EFI memory map only when installing a new one.

On Mon, 10 Jun 2024 at 22:09, Ard Biesheuvel <ardb+git@...gle.com> wrote:
>
> From: Ard Biesheuvel <ardb@...nel.org>
>
> The logic in __efi_memmap_init() is shared between two different
> execution flows:
> - mapping the EFI memory map early or late into the kernel VA space, so
>   that its entries can be accessed;
> - cloning the EFI memory map in order to insert new entries that are
>   created as a result of creating a memory reservation
>   (efi_arch_mem_reserve())
>
> In the former case, the underlying memory containing the kernel's view
> of the EFI memory map (which may be heavily modified by the kernel
> itself on x86) is not modified at all, and the only thing that changes
> is the virtual mapping of this memory, which is different between early
> and late boot.
>
> In the latter case, an entirely new allocation is created that carries a
> new, updated version of the kernel's view of the EFI memory map. When
> installing this new version, the old version will no longer be
> referenced, and if the memory was allocated by the kernel, it will leak
> unless it gets freed.
>
> The logic that implements this freeing currently lives on the code path
> that is shared between these two use cases, but it should only apply to
> the latter. So move it to the correct spot.
>
> Cc: Ashish Kalra <Ashish.Kalra@....com>
> Cc: Dave Young <dyoung@...hat.com>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Link: https://lore.kernel.org/all/36ad5079-4326-45ed-85f6-928ff76483d3@amd.com
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  arch/x86/platform/efi/memmap.c | 5 +++++
>  drivers/firmware/efi/memmap.c  | 5 -----
>  2 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/platform/efi/memmap.c b/arch/x86/platform/efi/memmap.c
> index 4ef20b49eb5e..4990244e5168 100644
> --- a/arch/x86/platform/efi/memmap.c
> +++ b/arch/x86/platform/efi/memmap.c
> @@ -97,6 +97,11 @@ int __init efi_memmap_install(struct efi_memory_map_data *data)
>         if (efi_enabled(EFI_PARAVIRT))
>                 return 0;
>
> +       if (efi.memmap.flags & (EFI_MEMMAP_MEMBLOCK | EFI_MEMMAP_SLAB))
> +               __efi_memmap_free(efi.memmap.phys_map,
> +                                 efi.memmap.desc_size * efi.memmap.nr_map,
> +                                 efi.memmap.flags);
> +
>         return __efi_memmap_init(data);

Nice fix!  but would it be better to save the old addr/size/flag and
free them only when __efi_memmap_init succeed?


>  }
>
> diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
> index 3365944f7965..3759e95a7407 100644
> --- a/drivers/firmware/efi/memmap.c
> +++ b/drivers/firmware/efi/memmap.c
> @@ -51,11 +51,6 @@ int __init __efi_memmap_init(struct efi_memory_map_data *data)
>                 return -ENOMEM;
>         }
>
> -       if (efi.memmap.flags & (EFI_MEMMAP_MEMBLOCK | EFI_MEMMAP_SLAB))
> -               __efi_memmap_free(efi.memmap.phys_map,
> -                                 efi.memmap.desc_size * efi.memmap.nr_map,
> -                                 efi.memmap.flags);
> -
>         map.phys_map = data->phys_map;
>         map.nr_map = data->size / data->desc_size;
>         map.map_end = map.map + data->size;
> --
> 2.45.2.505.gda0bf45e8d-goog
>