Re: [edk2-devel] [PATCH v2 0/3] OvmfPkg: Use QemuKernelLoaderFs to read cmdline/initrd

["Ard Biesheuvel" <ardb@kernel.org>]

On Thu, 17 Jun 2021 at 11:12, Dov Murik <dovmurik@linux.ibm.com> wrote:
>
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
>
> In order to support measured SEV boot with kernel/initrd/cmdline, we'd
> like to have one place that reads those blobs; in the future we'll add
> the measurement and verification in that place.
>
> We already have a synthetic filesystem (QemuKernelLoaderFs) which holds
> three files: "kernel", "initrd", and "cmdline".  The kernel is indeed
> read from this filesystem in LoadImage; but the cmdline (and the length
> of initrd) are read from QemuFwCfgLib items.
>
> This patch series modifies GenericQemuLoadImageLib to read cmdline (and
> the initrd size) from the QemuKernelLoaderFs synthetic filesystem, thus
> removing the dependency on QemuFwCfgLib.
>
> Note that X86QemuLoadImageLib is not modified, because it contains a
> QemuLoadLegacyImage() which reads other items of the QemuFwCfg which are
> not available in QemuKernelLoaderFs.  Since we don't want to support the
> legacy boot path in the future measured SEV boot, we leave
> X86QemuLoadImageLib as-is (except for a comment addition in patch 3) and
> will force use for GenericQemuLoadImageLib in the measured SEV boot
> implementation.
>
> Relevant discussion threads start in:
> https://edk2.groups.io/g/devel/message/76069
>
> To test this on x86_64, I forced the use of GenericQemuLoadImageLib
> using the following local patch:
>
>
> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
> index 0a237a905866..46442b543bcf 100644
> --- a/OvmfPkg/OvmfPkgX64.dsc
> +++ b/OvmfPkg/OvmfPkgX64.dsc
> @@ -404,7 +404,7 @@ [LibraryClasses.common.DXE_DRIVER]
>    PciLib|OvmfPkg/Library/DxePciLibI440FxQ35/DxePciLibI440FxQ35.inf
>    MpInitLib|UefiCpuPkg/Library/MpInitLib/DxeMpInitLib.inf
>    QemuFwCfgS3Lib|OvmfPkg/Library/QemuFwCfgS3Lib/DxeQemuFwCfgS3LibFwCfg.inf
> -  QemuLoadImageLib|OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.inf
> +  QemuLoadImageLib|OvmfPkg/Library/GenericQemuLoadImageLib/GenericQemuLoadImageLib.inf # XXX don't commit this or someone will be mad
>  !if $(TPM_ENABLE) == TRUE
>    Tpm12DeviceLib|SecurityPkg/Library/Tpm12DeviceLibTcg/Tpm12DeviceLibTcg.inf
>    Tpm2DeviceLib|SecurityPkg/Library/Tpm2DeviceLibTcg2/Tpm2DeviceLibTcg2.inf
>
>
> I tested boot with QEMU and OVMF with the following QEMU arguments:
>
>   -kernel a
>   -kernel a -initrd b
>   -kernel a -cmdline c
>   -kernel a -initrd b -cmdline c
>
> (and also without -kernel)
>
>
> Code is at
> https://github.com/confidential-containers-demo/edk2/tree/use-synthetic-fs-for-cmdline-v2
>
> v2 changes:
>
>  - Add comment to header of X86QemuLoadImageLib.inf
>  - Clearer function names in GenericQemuLoadImageLib.c
>  - Fix coding style issues
>
> v1: https://edk2.groups.io/g/devel/message/76265
>
>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Tobin Feldman-Fitzthum <tobin@linux.ibm.com>
>
> Dov Murik (3):
>   Revert "OvmfPkg/QemuKernelLoaderFsDxe: don't expose kernel command
>     line"
>   OvmfPkg/GenericQemuLoadImageLib: Read cmdline from QemuKernelLoaderFs
>   OvmfPkg/X86QemuLoadImageLib: State fw_cfg dependency in file header
>


Please cc me on the entire series.


>  OvmfPkg/Library/GenericQemuLoadImageLib/GenericQemuLoadImageLib.inf |   2 +-
>  OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.inf         |   3 +
>  OvmfPkg/Library/GenericQemuLoadImageLib/GenericQemuLoadImageLib.c   | 145 ++++++++++++++++++--
>  OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c           |   3 +
>  OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c               |  11 +-
>  5 files changed, 147 insertions(+), 17 deletions(-)
>
> --
> 2.25.1
>
>
>
> 
>
>