From: Tommaso Califano <[email protected]>
QEMU's AMD SEV support currently requires KVM on expensive AMD EPYC
hardware, limiting development and testing of SEV-aware guest software to
users with server-grade machines.
This series introduces a TCG-emulated SEV guest mode that enables SEV
validation without hardware dependencies, focusing on functional testing
rather than reproducing the hardware’s cryptographic context.
The emulation exposes SEV from the guest's perspective:
- Exposed CPUID leaf 0x8000001F to indicate active support.
- Active bit 0 in MSR 0xc0010131 to enable SEV on the guest.
- C-bit manipulation in PTEs/CR3 for paging consistency with the host.
- Complete SEV attestation workflow for injecting secrets into guest
memory (including direct kernel boot support).
The emulation uses a new QOM object "sev-emulated", derived from
"sev-guest", to maximize reuse of the existing SEV infrastructure while
maintaining a compiling dependency with KVM.
Below are the pros and cons of this choice.
In addition to inherited guest properties, two new ones are added (binary
files; default all-zero):
- tik: 16-byte Transport Integrity Key (TIK) for measurement HMAC.
- tek: 16-byte Transport Encryption Key (TEK) for secret payload
decryption.
Code reuse benefits:
- SEV detection via sev_enabled() and TYPE_SEV_COMMON object cast enables
the required checks for emulation without adding new conditions to the
codebase.
- QAPI fields for query-sev/launch-measure inherited from SevCommonState
and SevGuestState.
- Identical QMP interface (query-sev, query-sev-launch-measure,
sev-inject-launch-secret) as real SEV.
- Shared state machine (sev_set_guest_state()); override backend vtable
only (kvm_init → sev_emulated_init, launch_update_data, launch_finish,
sev_launch_get_measure).
Trade-offs:
- KVM linkage: sev-guest is KVM-centric; even if KVM is not used at
runtime, its code is required for compilation, so it is not possible to
use emulation with --disable-kvm.
Example usage:
-cpu "EPYC-Milan" \
-accel tcg \
-object sev-emulated,id=sev0,cbitpos=47,reduced-phys-bits=1,\
tik=/path/to/tik.bin,tek=/path/to/tek.bin \
-machine memory-encryption=sev0
Build requirements:
../qemu/configure --enable-gcrypt --enable-crypto-afalg
These provide libgcrypt support for crypto/hmac.h, crypto/cipher.h, and
crypto/random.h, used for:
- HMAC-SHA256 launch measurement (TIK key).
- Secret payload decryption (TEK key).
Note: --disable-kvm unsupported due to sev-guest inheritance (KVM code
linked, no runtime dependency).
Tommaso Califano (5):
i386/sev: Add sev-emulated QOM object with TCG support
target/i386: Add MSR SEV support and C-bit reset on TCG
i386/sev: Implement SEV launch state sequence and query-sev
i386/sev: Add launch measurement emulation and TIK property
i386/sev: Implement emulated launch secret injection and TEK property
accel/tcg/tcg-all.c | 18 +-
qapi/qom.json | 19 ++
target/i386/cpu.h | 2 +
target/i386/sev.c | 404 +++++++++++++++++++++++++++
target/i386/sev.h | 4 +
target/i386/tcg/system/excp_helper.c | 31 ++
target/i386/tcg/system/misc_helper.c | 13 +
7 files changed, 490 insertions(+), 1 deletion(-)
--
2.53.0
