[PATCH v3 0/2] [RESEND] x86/sev: Measured Linux SEV guest with kernel/initrd/cmdline

[Dov Murik]

(Resending for QEMU 6.2; no code changes since the last round.)

Currently booting with -kernel/-initrd/-append is not supported in SEV
confidential guests, because the content of these blobs is not measured
and therefore not trusted by the SEV guest.

However, in some cases the kernel, initrd, and cmdline are not secret
but should not be modified by the host.  In such a case, we want to
verify inside the trusted VM that the kernel, initrd, and cmdline are
indeed the ones expected by the Guest Owner, and only if that is the
case go on and boot them up (removing the need for grub inside OVMF in
that mode).

To support that, OVMF adds a special area for hashes of
kernel/initrd/cmdline; that area is expected to be filled by QEMU and
encrypted as part of the initial SEV guest launch.  This in turn makes
the hashes part of the PSP measured content, and OVMF can trust these
inputs if they match the hashes.

This series adds an SEV function to generate the table of hashes for
OVMF and encrypt it (patch 1/2), and calls this function if SEV is
enabled when the kernel/initrd/cmdline are prepared (patch 2/2).

Corresponding OVMF support [1] is already available in edk2 (patch series
"Measured SEV boot with kernel/initrd/cmdline").

[1] https://edk2.groups.io/g/devel/message/78250

---

v3: 
https://lore.kernel.org/qemu-devel/20210624102040.2015280-1-dovmurik@linux.ibm.com/
v3 changes:
 - initrd hash is now mandatory; if no -initrd is passed, calculate the
   hash of the empty buffer.  This is now aligned with the OVMF
   behaviour which verifies the empty initrd (correctly).
 - make SevHashTable entries fixed: 3 entries for cmdline, initrd, and kernel.
 - in sev_add_kernel_loader_hashes: first calculate all the hashes, only then
   fill-in the hashes table in the guest's memory.
 - Use g_assert_not_reached in sev-stub.c.
 - Use QEMU_PACKED attribute for structs.
 - Use QemuUUID type for guids.
 - in sev_add_kernel_loader_hashes: use ARRAY_SIZE(iov) instead of literal 2.

v2: 
https://lore.kernel.org/qemu-devel/20210621190553.1763020-1-dovmurik@linux.ibm.com/
v2 changes:
 - Extract main functionality to sev.c (with empty stub in sev-stub.c)
 - Use sev_enabled() instead of machine->cgs->ready to detect SEV guest
 - Coding style changes

v1: 
https://lore.kernel.org/qemu-devel/20210525065931.1628554-1-dovmurik@linux.ibm.com/

Dov Murik (2):
  sev/i386: Introduce sev_add_kernel_loader_hashes for measured linux
    boot
  x86/sev: generate SEV kernel loader hashes in x86_load_linux

 target/i386/sev_i386.h |  12 ++++
 hw/i386/x86.c          |  25 +++++++-
 target/i386/sev-stub.c |   5 ++
 target/i386/sev.c      | 137 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 178 insertions(+), 1 deletion(-)


base-commit: f9baca549e44791be0dd98de15add3d8452a8af0
-- 
2.25.1