linux-kernel - Re: [PATCH] efi/libstub/x86: Free EFI map buffer in allocate

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Date:   Wed, 6 May 2020 09:23:55 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Lenny Szubowicz <lszubowi@...hat.com>
Cc:     eric.snowberg@...cle.com, Ingo Molnar <mingo@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] efi/libstub/x86: Free EFI map buffer in allocate_e820()

On Tue, 5 May 2020 at 21:00, Lenny Szubowicz <lszubowi@...hat.com> wrote:
>
> In allocate_e820(), free the EFI map buffer that has been returned
> by efi_get_memory_map(). The returned size of the EFI map buffer
> is used to allocate an adequately sized e820ext buffer, if it's
> needed. But the contents of that EFI map buffer is not used at all
> and the local pointer to it is gone on return from allocate_e820().
>
> Signed-off-by: Lenny Szubowicz <lszubowi@...hat.com>
> ---
>  drivers/firmware/efi/libstub/x86-stub.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> index 05ccb229fb45..4efe3e7a218d 100644
> --- a/drivers/firmware/efi/libstub/x86-stub.c
> +++ b/drivers/firmware/efi/libstub/x86-stub.c
> @@ -623,6 +623,9 @@ static efi_status_t allocate_e820(struct boot_params *params,
>         if (status != EFI_SUCCESS)
>                 return status;
>
> +       /* Allocated EFI map buf is not used here. Just need its size. */
> +       efi_bs_call(free_pool, map);
> +

Wouldn't it be better to call BS->GetMemoryMap() directly here, with a
zero size for the input buffer?

>         nr_desc = buff_size / desc_size;
>
>         if (nr_desc > ARRAY_SIZE(params->e820_table)) {
> --
> 2.18.4
>