linux-kernel - Re: [PATCH v2] efi_64: Fix a missing-check bug in arch/x86/platform/efi/efi

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Date:   Fri, 24 May 2019 18:07:10 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Gen Zhang <blackgod016574@...il.com>
Cc:     Darren Hart <dvhart@...radead.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] efi_64: Fix a missing-check bug in arch/x86/platform/efi/efi_64.c

On Thu, 23 May 2019 at 02:51, Gen Zhang <blackgod016574@...il.com> wrote:
>
> In efi_call_phys_prolog(), save_pgd is allocated by kmalloc_array().
> And it is dereferenced in the following codes. However, memory
> allocation functions such as kmalloc_array() may fail. Dereferencing
> this save_pgd null pointer may cause the kernel go wrong. Thus we
> should check this allocation.
> Further, if efi_call_phys_prolog() returns NULL, we should abort the
> process in phys_efi_set_virtual_address_map(), and return EFI_ABORTED.
>
> Signed-off-by: Gen Zhang <blackgod016574@...il.com>
>
> ---
> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> index e1cb01a..a7189a3 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -85,6 +85,8 @@ static efi_status_t __init phys_efi_set_virtual_address_map(
>         pgd_t *save_pgd;
>
>         save_pgd = efi_call_phys_prolog();
> +       if (!save_pgd)
> +               return EFI_ABORTED;
>
>         /* Disable interrupts around EFI calls: */
>         local_irq_save(flags);
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index cf0347f..828460a 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -91,6 +91,8 @@ pgd_t * __init efi_call_phys_prolog(void)
>
>         n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE);
>         save_pgd = kmalloc_array(n_pgds, sizeof(*save_pgd), GFP_KERNEL);
> +       if (!save_pgd)
> +               return NULL;
>
>         /*
>          * Build 1:1 identity mapping for efi=old_map usage. Note that
> ---

Apologies for only spotting this now, but I seem to have given some bad advice.

efi_call_phys_prolog() in efi_64.c will also return NULL if
(!efi_enabled(EFI_OLD_MEMMAP)), but this is not an error condition. So
that occurrence has to be updated: please return efi_mm.pgd instead.