On 06/01/21 15:20, Ard Biesheuvel wrote:
> On Tue, 1 Jun 2021 at 14:12, Laszlo Ersek <ler...@redhat.com> wrote:
>>
> ...
>> - A major complication for hashing all three of: kernel, initrd,
>> cmdline, is that the *fetching* of this triplet is split between two
>> places. (Well, it is split between *three* places in fact, but I'm
>> going to ignore LinuxInitrdDynamicShellCommand for now, because the
>> AmdSevX64 platform sets BUILD_SHELL to FALSE for production.)
>>
>> The kernel and the initrd are fetched in QemuKernelLoaderFsDxe, but
>> the command line is fetched in (both) QemuLoadImageLib instances.
>> This requires that all these modules be littered with hashing as
>> well, which I find *really bad*. Even if we factor out the actual
>> logic, I strongly dislike having *just hooks* for hashing in multiple
>> modules.
>>
>> Now, please refer to efc52d67e157 ("OvmfPkg/QemuKernelLoaderFsDxe:
>> don't expose kernel command line", 2020-03-05). If we first
>>
>> (a) reverted that commit, and
>>
>> (b) modified *both* QemuLoadImageLib instances, to load the kernel
>> command line from the *synthetic filesystem* (rather than directly
>> from fw_cfg),
>>
>> then we could centralize the hashing to just QemuKernelLoaderFsDxe.
>>
>> Ard -- what's your thought on this?
>>
>
> I don't have any problems with that - I take it this means we can drop
> the QemuFwCfgLib dependency from GenericQemuLoadImageLib altogether,
> right?
A bit more work is needed for that (but I agree it should be done),
because we have this additionally:
QemuFwCfgSelectItem (QemuFwCfgItemInitrdSize);
InitrdSize = (UINTN)QemuFwCfgRead32 ();
if (InitrdSize > 0) {
//
// Append ' initrd=initrd' in UTF-16.
//
KernelLoadedImage->LoadOptionsSize += sizeof (L" initrd=initrd") - 2;
}
This should also be rebased on top of the synthetic filesystem [*], and
then no more QemuFwCfgLib calls should remain.
[*] From StubFileOpen() in "QemuKernelLoaderFsDxe.c", it seems that we
successfully open zero-sized fw_cfg files. (We also list them, when
reading the root directory, in StubFileRead()). That's not a problem
at all, but it means that, after opening the initrd file temporarily
in QemuLoadImageLib, EFI_FILE_PROTOCOL.GetInfo() should be used for
fetching an EFI_FILE_INFO, and then EFI_FILE_INFO.FileSize needs to
be compared to 0.
>
>>
>> And then, we could eliminate the dynamic callback registration, plus
>> the separate SevFwCfgVerifier, SevHashFinderLib, and
>> SevQemuLoadImageLib stuff.
>>
>> We'd only need one new lib class, with *statically linked* hooks for
>> QemuKernelLoaderFsDxe, and two instances of this new class, a Null
>> one, and an actual (SEV hash verifier) one. The latter instance would
>> locate the hash values, calculate the fresh hashes, and perform the
>> comparisons. Only the AmdSevX64 platform would use the non-Null
>> instance of this library class.
>>
>> (NB QemuKernelLoaderFsDxe is used by some ArmVirtPkg platforms, so
>> resolutions to the Null instance would be required there too.)
>>
>
> This sounds like a good approach to me.
Thank you!
Laszlo
>
>
>>
>>>
>>> Cc: Laszlo Ersek <ler...@redhat.com>
>>> Cc: Ard Biesheuvel <ardb+tianoc...@kernel.org>
>>> Cc: Jordan Justen <jordan.l.jus...@intel.com>
>>> Cc: Ashish Kalra <ashish.ka...@amd.com>
>>> Cc: Brijesh Singh <brijesh.si...@amd.com>
>>> Cc: Erdem Aktas <erdemak...@google.com>
>>> Cc: James Bottomley <j...@linux.ibm.com>
>>> Cc: Jiewen Yao <jiewen....@intel.com>
>>> Cc: Min Xu <min.m...@intel.com>
>>> Cc: Tom Lendacky <thomas.lenda...@amd.com>
>>>
>>> James Bottomley (8):
>>> OvmfPkg/AmdSev/SecretDxe: fix header comment to generic naming
>>> OvmfPkg: PlatformBootManagerLibGrub: Allow executing kernel via fw_cfg
>>> OvmfPkg/AmdSev: add a page to the MEMFD for firmware config hashes
>>> OvmfPkg/QemuKernelLoaderFsDxe: Add ability to verify loaded items
>>> OvmfPkg/AmdSev: Add library to find encrypted hashes for the FwCfg
>>> device
>>> OvmfPkg/AmdSev: Add firmware file plugin to verifier
>>> OvmfPkg: GenericQemuLoadImageLib: Allow verifying fw_cfg command line
>>> OvmfPkg/AmdSev: add SevQemuLoadImageLib
>>>
>>> OvmfPkg/OvmfPkg.dec
>>> | 10 ++
>>> OvmfPkg/AmdSev/AmdSevX64.dsc
>>> | 9 +-
>>> OvmfPkg/AmdSev/AmdSevX64.fdf
>>> | 3 +
>>> OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.inf
>>> | 30 +++++
>>> OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.inf
>>> | 34 ++++++
>>> OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.inf
>>> | 30 +++++
>>> OvmfPkg/Library/PlatformBootManagerLibGrub/PlatformBootManagerLibGrub.inf
>>> | 2 +
>>> OvmfPkg/ResetVector/ResetVector.inf
>>> | 2 +
>>> OvmfPkg/AmdSev/Include/Library/SevHashFinderLib.h
>>> | 47 ++++++++
>>> OvmfPkg/Include/Library/QemuFwCfgLib.h
>>> | 35 ++++++
>>> OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.h
>>> | 11 ++
>>> OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.c
>>> | 60 ++++++++++
>>> OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.c
>>> | 126 ++++++++++++++++++++
>>> OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.c
>>> | 52 ++++++++
>>> OvmfPkg/AmdSev/SecretDxe/SecretDxe.c
>>> | 2 +-
>>> OvmfPkg/Library/GenericQemuLoadImageLib/GenericQemuLoadImageLib.c
>>> | 29 +++++
>>> OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.c
>>> | 5 +
>>> OvmfPkg/Library/PlatformBootManagerLibGrub/QemuKernel.c
>>> | 50 ++++++++
>>> OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c
>>> | 31 +++++
>>> OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm
>>> | 20 ++++
>>> OvmfPkg/ResetVector/ResetVector.nasmb
>>> | 2 +
>>> 21 files changed, 587 insertions(+), 3 deletions(-)
>>> create mode 100644
>>> OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.inf
>>> create mode 100644
>>> OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.inf
>>> create mode 100644
>>> OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.inf
>>> create mode 100644 OvmfPkg/AmdSev/Include/Library/SevHashFinderLib.h
>>> create mode 100644
>>> OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.c
>>> create mode 100644
>>> OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.c
>>> create mode 100644
>>> OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.c
>>> create mode 100644 OvmfPkg/Library/PlatformBootManagerLibGrub/QemuKernel.c
>>>
>>
>
>
>
>
>
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#75919): https://edk2.groups.io/g/devel/message/75919
Mute This Topic: https://groups.io/mt/83074450/21656
Group Owner: devel+ow...@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com]
-=-=-=-=-=-=-=-=-=-=-=-
