linux-kernel - Re: [PATCH v2] efi: Ignore unrealistically large option roms

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Date:   Sat, 28 Apr 2018 08:40:59 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        linux-efi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] efi: Ignore unrealistically large option roms

Hi Hans,

On 27 April 2018 at 23:35, Hans de Goede <hdegoede@...hat.com> wrote:
> setup_efi_pci() tries to save a copy of each PCI option ROM as this may
> be necessary for the device driver for the PCI device to have access too.
>
> On some systems the efi_pci_io_protocol_64's romimage and romsize fields
> contain invalid data, which looks a bit like pointers pointing back into
> other EFI code or data. Interpreting these pointers as romsize leads to
> a very large value and if we then try to alloc this amount of memory to
> save a copy the alloc call fails.
>
> This leads to a "Failed to alloc mem for rom" error being printed on the
> EFI console for each PCI device.
>
> This commit avoids the printing of these errors, by checking romsize
> before doing the alloc and if it is larger then 256M silently ignore the
> ROM fields instead of trying to alloc mem and fail.
>

The UEFI spec limits the size of option ROMs to 16 MiB, so I'd prefer
we use that as the upper bound instead.

With that changed,

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

or I can take it via the EFI tree if desired.

-- 
Ard.


> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> ---
> Changes in v2:
> -Add the check to both __setup_efi_pci32 and __setup_efi_pci64 instead of
>  only to __setup_efi_pci64, some CHT devices which need this still use a
>  32 bit UEFI
> ---
>  arch/x86/boot/compressed/eboot.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
> index 47d3efff6805..6d3257a459c8 100644
> --- a/arch/x86/boot/compressed/eboot.c
> +++ b/arch/x86/boot/compressed/eboot.c
> @@ -122,7 +122,13 @@ __setup_efi_pci32(efi_pci_io_protocol_32 *pci, struct pci_setup_rom **__rom)
>         if (status != EFI_SUCCESS)
>                 return status;
>
> -       if (!pci->romimage || !pci->romsize)
> +       /*
> +        * Some firmwares contain EFI function pointers at the place where the
> +        * romimage and romsize fields are supposed to be. Typically the EFI
> +        * code is mapped at high addresses, translating to an unrealistically
> +        * large romsize. We reject any roms over 256M in size to catch this.
> +        */
> +       if (!pci->romimage || !pci->romsize || pci->romsize > 0x10000000)
>                 return EFI_INVALID_PARAMETER;
>
>         size = pci->romsize + sizeof(*rom);
> @@ -230,7 +236,13 @@ __setup_efi_pci64(efi_pci_io_protocol_64 *pci, struct pci_setup_rom **__rom)
>         if (status != EFI_SUCCESS)
>                 return status;
>
> -       if (!pci->romimage || !pci->romsize)
> +       /*
> +        * Some firmwares contain EFI function pointers at the place where the
> +        * romimage and romsize fields are supposed to be. Typically the EFI
> +        * code is mapped at high addresses, translating to an unrealistically
> +        * large romsize. We reject any roms over 256M in size to catch this.
> +        */
> +       if (!pci->romimage || !pci->romsize || pci->romsize > 0x10000000)
>                 return EFI_INVALID_PARAMETER;
>
>         size = pci->romsize + sizeof(*rom);
> --
> 2.16.2
>