Re: [Xen-devel] [PATCH 0/4] x86/xen/efi: Initialize UEFI secure boot state during dom0 boot

[Ard Biesheuvel]

On 12 January 2018 at 11:24, Daniel Kiper  wrote:
> Hi Ard,
>
> On Thu, Jan 11, 2018 at 12:51:07PM +, Ard Biesheuvel wrote:
>> On 9 January 2018 at 14:22, Daniel Kiper  wrote:
>> > Hi,
>> >
>> > Initialize UEFI secure boot state during dom0 boot. Otherwise the kernel
>> > may not even know that it runs on secure boot enabled platform.
>>
>> Hi Daniel,
>>
>> I must say, I am not too thrilled with the approach you have chosen
>> here. #including .c files in other .c files, and using #defines to
>> override C functions or other stub functionality is rather fragile. In
>
> TBH I do not like it too. Sadly I have not find a better solution for
> that. I wish to avoid code duplication as much as possible because
> otherwise it will fall out of sync sooner or later (usually sooner).
> Similar thing happened in different part of Xen EFI code a few months ago.
>
>> particular, it means we have to start caring about not breaking
>> Xen/x86 code when making modifications to the EFI stub, and that code
>> is already difficult enough to maintain, given that it is shared
>> between ARM, arm64 and x86, and runs either from the decompressor or
>> the kernel proper (arm64) but in the context of the UEFI firmware.
>
> I understand that.
>
>> None of the stub code currently runs in ordinary kernel context.
>
> Yep.
>
>> So please, could you try to find another way to do this?
>
> I am happy to improve the situation, however, I am afraid that it is
> difficult here. Stub and kernel proper are separate entities and simple
> linking does not work. So, It seems to me that only play with includes
> will allow us to not duplicate the code. However, if you have a better
> idea I am happy to implement it.
>

Actually, there is another reason why it does not make sense to reuse that code.

This code

/*
* See if a user has put the shim into insecure mode. If so, and if the
* variable doesn't have the runtime attribute set, we might as well
* honor that.
*/
size = sizeof(moksbstate);
status = get_efi_var(L"MokSBState", _guid,
 , , );

/* If it fails, we don't care why. Default to secure */
if (status != EFI_SUCCESS)
goto secure_boot_enabled;
if (!(attr & EFI_VARIABLE_RUNTIME_ACCESS) && moksbstate == 1)
return efi_secureboot_mode_disabled;

will always fail after exiting boot services, so it makes no sense to
call it from xen_efi_init().

So I suggest you just clone the function and only keep the pieces that
make sense for Xen.

-- 
Ard.

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Re: [Xen-devel] [PATCH 0/4] x86/xen/efi: Initialize UEFI secure boot state during dom0 boot

[Daniel Kiper]

Hi Ard,

On Thu, Jan 11, 2018 at 12:51:07PM +, Ard Biesheuvel wrote:
> On 9 January 2018 at 14:22, Daniel Kiper  wrote:
> > Hi,
> >
> > Initialize UEFI secure boot state during dom0 boot. Otherwise the kernel
> > may not even know that it runs on secure boot enabled platform.
>
> Hi Daniel,
>
> I must say, I am not too thrilled with the approach you have chosen
> here. #including .c files in other .c files, and using #defines to
> override C functions or other stub functionality is rather fragile. In

TBH I do not like it too. Sadly I have not find a better solution for
that. I wish to avoid code duplication as much as possible because
otherwise it will fall out of sync sooner or later (usually sooner).
Similar thing happened in different part of Xen EFI code a few months ago.

> particular, it means we have to start caring about not breaking
> Xen/x86 code when making modifications to the EFI stub, and that code
> is already difficult enough to maintain, given that it is shared
> between ARM, arm64 and x86, and runs either from the decompressor or
> the kernel proper (arm64) but in the context of the UEFI firmware.

I understand that.

> None of the stub code currently runs in ordinary kernel context.

Yep.

> So please, could you try to find another way to do this?

I am happy to improve the situation, however, I am afraid that it is
difficult here. Stub and kernel proper are separate entities and simple
linking does not work. So, It seems to me that only play with includes
will allow us to not duplicate the code. However, if you have a better
idea I am happy to implement it.

Daniel

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Re: [Xen-devel] [PATCH 0/4] x86/xen/efi: Initialize UEFI secure boot state during dom0 boot

[Ard Biesheuvel]

On 9 January 2018 at 14:22, Daniel Kiper  wrote:
> Hi,
>
> Initialize UEFI secure boot state during dom0 boot. Otherwise the kernel
> may not even know that it runs on secure boot enabled platform.
>

Hi Daniel,

I must say, I am not too thrilled with the approach you have chosen
here. #including .c files in other .c files, and using #defines to
override C functions or other stub functionality is rather fragile. In
particular, it means we have to start caring about not breaking
Xen/x86 code when making modifications to the EFI stub, and that code
is already difficult enough to maintain, given that it is shared
between ARM, arm64 and x86, and runs either from the decompressor or
the kernel proper (arm64) but in the context of the UEFI firmware.
None of the stub code currently runs in ordinary kernel context.

So please, could you try to find another way to do this?

Thanks,
Ard.


>
>  arch/x86/xen/Makefile  |4 +++-
>  arch/x86/xen/efi.c |   14 +
>  drivers/firmware/efi/libstub/secureboot-core.c |   77 
> +
>  drivers/firmware/efi/libstub/secureboot.c  |   66 
> +--
>  4 files changed, 99 insertions(+), 62 deletions(-)
>
> Daniel Kiper (4):
>   efi/stub: Extract efi_get_secureboot() to separate file
>   x86/xen/efi: Initialize boot_params.secure_boot in xen_efi_init()
>   efi: Tweak efi_get_secureboot() and its data section assignment
>   efi: Rename efi_get_secureboot() to __efi_get_secureboot() and make it 
> static
>

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[Xen-devel] [PATCH 0/4] x86/xen/efi: Initialize UEFI secure boot state during dom0 boot

[Daniel Kiper]

Hi,

Initialize UEFI secure boot state during dom0 boot. Otherwise the kernel
may not even know that it runs on secure boot enabled platform.

Daniel

 arch/x86/xen/Makefile  |4 +++-
 arch/x86/xen/efi.c |   14 +
 drivers/firmware/efi/libstub/secureboot-core.c |   77 
+
 drivers/firmware/efi/libstub/secureboot.c  |   66 
+--
 4 files changed, 99 insertions(+), 62 deletions(-)

Daniel Kiper (4):
  efi/stub: Extract efi_get_secureboot() to separate file
  x86/xen/efi: Initialize boot_params.secure_boot in xen_efi_init()
  efi: Tweak efi_get_secureboot() and its data section assignment
  efi: Rename efi_get_secureboot() to __efi_get_secureboot() and make it 
static


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