Re: [PATCH] efi: bump efistub version from 1.1 to 3.0 for VZLinuxBootLoader compatibility

[Akihiro Suda]

> > I'll queue this as a fix, but I'm going to tweak the comment (and the
> > commit log) a bit, if you don't mind

Thank you for rewriting my comments, but the new comments seem
slightly incorrect:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=36e4fc57fc1619f462e669e939209c45763bc8f5

> efi: Bump stub image version for macOS HVF compatibility

The commit is about Virtualization.framework, not about
Hypervisor.framework (HVF).

Virtualization.framework = high-level VMM, similar to QEMU
(/usr/bin/qemu-system-*)
Hypervisor.framework     = low-level  VMM, similar to kvm.ko

> The macOS hypervisor framework includes a host-side VMM called VZLinuxBootLoader

VZLinuxBootLoader is a part of Virtualization.framework, not
Hypervisor.framework.
Also, VZLinuxBootLoader is not a VMM; it is just an API for loading
vmlinuz into Virtualization.framework.
(similar to the `-kernel` and the `-initrd` flags of QEMU)

> On x86, it incorporates a BIOS style loader that does not implement or expose EFI to the loaded kernel.

AFAICS, it does not seem to use real mode BIOS.



2023年5月29日(月) 9:51 Akihiro Suda <suda.kyoto@xxxxxxxxx>:
>
> > > The next version will be 7 (0b111).
> >
> > How so? If this is going to be a monotonically increasing sequence
> > after all, it is still not a bit mask, and this change defeats the
> > purpose.
>
> Sorry, I forgot to append ", if it will retain compatibility with 0b11".
>
> > I'll queue this as a fix, but I'm going to tweak the comment (and the
> > commit log) a bit, if you don't mind
>
> Thanks, please feel free to tweak that.
>
> > I'd appreciate it if you still report this as a bug with Apple, though.
>
> Reported via https://www.apple.com/feedback/macos.html
>
>
> 2023年5月29日(月) 3:48 Ard Biesheuvel <ardb@xxxxxxxxxx>:
> >
> > On Sun, 28 May 2023 at 09:59, Akihiro Suda <suda.kyoto@xxxxxxxxx> wrote:
> > >
> > > - LINUX_EFISTUB_MAJOR_VERSION is bumped from 1 (0b1) to 3 (0b11).
> > >   The value is now a bitfield.
> > >
> >
> > OK
> >
> > > The next version will be 7 (0b111).
> >
> > How so? If this is going to be a monotonically increasing sequence
> > after all, it is still not a bit mask, and this change defeats the
> > purpose.
> >
> > > - LINUX_EFISTUB_MINOR_VERSION is pinned to 0x0, because Apple's
> > >   VZLinuxBootLoader [1] cannot boot a kernel with other minor version value [2],
> > >   even though it does not use UEFI. Tested with macOS 13.4 (x86_64).
> > >
> > > [1] https://developer.apple.com/documentation/virtualization/vzlinuxbootloader
> > > [2] https://lore.kernel.org/linux-efi/CAG8fp8Teu4G9JuenQrqGndFt2Gy+V4YgJ=hN1xX7AD940YKf3A@xxxxxxxxxxxxxx/
> > >
> > > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217485
> > > Signed-off-by: Akihiro Suda <akihiro.suda.cz@xxxxxxxxxxxxx>
> >
> > I'll queue this as a fix, but I'm going to tweak the comment (and the
> > commit log) a bit, if you don't mind
> >
> > I'd appreciate it if you still report this as a bug with Apple, though.
> >
> > Thanks,
> > Ard.
> >
> > > ---
> > >  include/linux/pe.h | 20 ++++++++++++++++++--
> > >  1 file changed, 18 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/linux/pe.h b/include/linux/pe.h
> > > index 5e1e11540870..ee5ade19b7eb 100644
> > > --- a/include/linux/pe.h
> > > +++ b/include/linux/pe.h
> > > @@ -27,9 +27,25 @@
> > >   * On x86, LoadImage() and StartImage() can be omitted if the EFI handover
> > >   * protocol is implemented, which can be inferred from the version,
> > >   * handover_offset and xloadflags fields in the bootparams structure.
> > > + *
> > > + * Linux EFI stub v1.1 unconditionally enabled initrd command line loader,
> > > + * which was previously gated by CONFIG_EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER.
> > > + *
> > > + * Linux EFI stub v3.0 changed the major version to be a bitfield (0b11).
> > > + * The rightmost bit means that it is compatible with v1.0 at least.
> > > + * The second rightmost bit means that initrd command line loader is enabled.
> > > + * So, there is no v2.0 (0b10), and the next version will be v7.0 (0b111).
> > > + */
> > > +#define LINUX_EFISTUB_MAJOR_VERSION            0x3
> > > +
> > > +/*
> > > + * LINUX_EFISTUB_MINOR_VERSION is pinned to 0x0, because Apple's
> > > + * VZLinuxBootLoader cannot boot a kernel with other minor version value, even
> > > + * though it does not use UEFI. Tested with macOS 13.4 (x86_64).
> > > + *
> > > + * https://lore.kernel.org/linux-efi/CAG8fp8Teu4G9JuenQrqGndFt2Gy+V4YgJ=hN1xX7AD940YKf3A@xxxxxxxxxxxxxx/
> > >   */
> > > -#define LINUX_EFISTUB_MAJOR_VERSION            0x1
> > > -#define LINUX_EFISTUB_MINOR_VERSION            0x1
> > > +#define LINUX_EFISTUB_MINOR_VERSION            0x0
> > >
> > >  /*
> > >   * LINUX_PE_MAGIC appears at offset 0x38 into the MS-DOS header of EFI bootable
> > > --
> > > 2.39.2