Re: [PATCH edk2-platforms v3 1/5] Hisilicon/D0x: Fix secure boot bug in FlashFvbDxe

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Tue, 20 Nov 2018 at 15:30, Ming Huang <ming.huang@linaro.org> wrote:
>
>
>
> On 11/20/2018 8:58 PM, Leif Lindholm wrote:
> > On Tue, Nov 20, 2018 at 08:40:28PM +0800, Ming Huang wrote:
> >>
> >>
> >> On 11/20/2018 8:13 PM, Leif Lindholm wrote:
> >>> On Tue, Nov 20, 2018 at 05:01:46PM +0800, Ming Huang wrote:
> >>>> Now that the generic Variable Runtime DXE code no longer
> >>>> distinguishes between gEfiVariableGuid and
> >>>> gEfiAuthenticatedVariableGuid in the varstore FV header.
> >>>> We can relax the check in the flashFvb driver to accept
> >>>> either GUID regardless of whether we are running a secure
> >>>> boot capable build or not.
> >>>
> >>> We are still in a situation where D06 is not buildable with Secure
> >>> Boot enabled though.
> >>>
> >>> If you build with -D SECURE_BOOT_ENABLE=TRUE, you still end up with
> >>> /work/git/edk2-platforms/Platform/Hisilicon/D06/D06.dsc(...): error
> >>> 4000: Instance of library class [PlatformSecureLib] is not found
> >>>       in [/work/git/edk2/SecurityPkg/VariableAuthenticated/SecureBootConfigDxe/SecureBootConfigDxe.inf] [AARCH64]
> >>>       consumed by module [/work/git/edk2/SecurityPkg/VariableAuthenticated/SecureBootConfigDxe/SecureBootConfigDxe.inf]
> >>>
> >>> And all Hisilicon platforms still use
> >>> AuthVariableLib|MdeModulePkg/Library/AuthVariableLibNull/AuthVariableLibNull.inf
> >>> regardless of Secure Boot setting.
> >>>
> >>> So what problem does this patch solve? A runtime one?
> >>
> >> This patch solve bug in FlashFvbDxe.
> >
> > Yes, but what bug? What is the symptom? What _specific_ problem goes
> > away by adding this patch? That information should have been in the
> > original commit message. I have no information available to me as I
> > now build -rc1 to suggest that this patch should be included.
>
> The bug is that gEfiAuthenticatedVariableGuid should be used in FlashFvbDxe,
> not gEfiVariableGuid when enable secure boot.
>
> >
> >> Should I add a patch before this patch
> >> to solve build error with -D SECURE_BOOT_ENABLE=TRUE in v4?
> >
> > That would require a sane implementation of PlatformSecureLib,
> > implementing a real UserPhysicalPresent().
> > Can you turn that around within the next few hours?
>
> My original idea is using OvmfPkg/Library/PlatformSecureLib/PlatformSecureLib.
> There is not enough time to implement a real UserPhysicalPresent.
> This patch will add when we implement real secure boot in future.
>

I think it is a terrible idea to enable secure boot now in an insecure
manner, and enable 'real' secure boot later.

Note that it is impossible to implement secure boot in a secure manner
using the generic VariableRuntimeDxe. The crypto routines that perform
the authentication are located in EfiRuntimeServicesCode memory
regions, which are writable by the OS, and so any exploit on the OS
side can modify that code to defeat the checks. Also, the SPI flash
that backs the variable store is accessible by the OS directly.

That means a proper secure boot implementation will not be based on
any of the components in use currently, and so enabling it does
nothing except confuse people or give them a false sense of security.
If this is based on OS or firmware test results, please disregard
those - this is a tick the box mentality that is wholly incompatible
with building secure systems.