[PATCH v9 00/24] Add Secure TSC support for SNP guests

Nikunj A Dadhania
2024-05-31T04:31:23Z

This patchset is also available at:

https://github.com/AMDESE/linux-kvm/tree/sectsc-guest-latest

and is based on commit: 1613e604df0c ("Linux 6.10-rc1")

Overview
--------

Secure TSC allows guests to securely use RDTSC/RDTSCP instructions as the
parameters being used cannot be changed by hypervisor once the guest is
launched. More details in the AMD64 APM Vol 2, Section "Secure TSC".

During the boot-up of the secondary cpus, SecureTSC enabled guests need to
query TSC info from AMD Security Processor. This communication channel is
encrypted between the AMD Security Processor and the guest, the hypervisor
is just the conduit to deliver the guest messages to the AMD Security
Processor. Each message is protected with an AEAD (AES-256 GCM). See "SEV
Secure Nested Paging Firmware ABI Specification" document (currently at
https://www.amd.com/system/files/TechDocs/56860.pdf) section "TSC Info"

Use a minimal GCM library to encrypt/decrypt SNP Guest messages to
communicate with the AMD Security Processor which is available at early
boot.

SEV-guest driver has the implementation for guest and AMD Security
Processor communication. As the TSC_INFO needs to be initialized during
early boot before smp cpus are started, move most of the sev-guest driver
code to kernel/sev.c and provide well defined APIs to the sev-guest driver
to use the interface to avoid code-duplication.

Patches:
01-09: Preparatory patches for code movement and general cleanup/fixups
10-13: Patches moving SNP guest messaging code from SEV guest driver to
SEV common code
14-16: Error handling and caching secrets page
17-24: SecureTSC enablement patches.

Testing SecureTSC
-----------------

SecureTSC hypervisor patches based on top of SEV-SNP Guest MEMFD series:
https://github.com/AMDESE/linux-kvm/tree/sectsc-host-latest

QEMU changes:
https://github.com/nikunjad/qemu/tree/snp-securetsc-latest

QEMU commandline SEV-SNP with SecureTSC:

qemu-system-x86_64 -cpu EPYC-Milan-v2,+invtsc -smp 4 \
-object memory-backend-memfd,id=ram1,size=1G,share=true,prealloc=false,reserve=false \
-object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1,secure-tsc=on \
-machine q35,confidential-guest-support=sev0,memory-backend=ram1 \
...

Changelog:
----------
v9:
* Added Acked-by/Reviewed-by
* Removed Reviewed-by/Tested-by from patches that had significant changes
* Added patch to make payload a variable length array in snp_guest_msg
* Fix all your user-visible strings (vmpck => VMPCK) and readabilty.
* Separated patch for message sequence handling
* Handle failures from snp_init() in sme_enable()
* Preparatory patches:
* Carved out simplify VMPCK and OS message sequence changes
* Carved out SNP guest messaging init/exit for proper initialization and
cleanup.
* Move SNP command mutex down and make it private to sev.c
* Pure code movement patch and subsequent code changes patches
* Drop patches adding guest initiation hook enc_init() and call
snp_secure_tsc_prepare() from mem_encrypt.c
* Use CC_ATTR_GUEST_SECURE_TSC and drop synthetic SecureTSC feature bit

v8: https://lore.kernel.org/lkml/20240215113128.275608-1-nikunj@amd.com/
* Rebased on top of tip/x86/sev
* Use minimum size of IV or msg_seqno in memcpy
* Use arch/x86/include/asm/sev.h instead of sev-guest.h
* Use DEFINE_MUTEX for snp_guest_cmd_mutex
* Added Reviewed-by from Tom.
* Dropped Tested-by from patch 3/16

v7: https://lore.kernel.org/kvm/20231220151358.2147066-1-nikunj@amd.com/
v6: https://lore.kernel.org/lkml/20231128125959.1810039-1-nikunj@amd.com/
v5: https://lore.kernel.org/lkml/20231030063652.68675-1-nikunj@amd.com/
v4: https://lore.kernel.org/lkml/20230814055222.1056404-1-nikunj@amd.com/
v3: https://lore.kernel.org/lkml/20230722111909.15166-1-nikunj@amd.com/
v2: https://lore.kernel.org/r/20230307192449.24732-1-bp@alien8.de/
v1: https://lore.kernel.org/r/20230130120327.977460-1-nikunj@amd.com

Nikunj A Dadhania (24):
virt: sev-guest: Use AES GCM crypto library
virt: sev-guest: Replace dev_dbg with pr_debug
virt: sev-guest: Make payload a variable length array
virt: sev-guest: Add SNP guest request structure
virt: sev-guest: Fix user-visible strings
virt: sev-guest: Simplify VMPCK and sequence number assignments
virt: sev-guest: Store VMPCK index to SNP guest device structure
virt: sev-guest: Take mutex in snp_send_guest_request()
virt: sev-guest: Carve out SNP guest messaging init/exit
x86/sev: Move core SEV guest driver routines to common code
x86/sev: Replace dev_[err,alert] with pr_[err,alert]
x86/sev: Make snp_issue_guest_request() static
x86/sev: Make sev-guest driver functional again
x86/sev: Handle failures from snp_init()
x86/sev: Cache the secrets page address
x86/sev: Drop sev_guest_platform_data structure
x86/cc: Add CC_ATTR_GUEST_SECURE_TSC
x86/sev: Add Secure TSC support for SNP guests
x86/sev: Change TSC MSR behavior for Secure TSC enabled guests
x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled
guests
x86/kvmclock: Skip kvmclock when Secure TSC is available
x86/sev: Mark Secure TSC as reliable
x86/cpu/amd: Do not print FW_BUG for Secure TSC
x86/sev: Enable Secure TSC for SNP guests

arch/x86/include/asm/sev-common.h | 1 +
arch/x86/include/asm/sev.h | 197 ++++++-
arch/x86/include/asm/svm.h | 6 +-
drivers/virt/coco/sev-guest/sev-guest.h | 63 ---
include/linux/cc_platform.h | 8 +
arch/x86/boot/compressed/sev.c | 3 +-
arch/x86/coco/core.c | 3 +
arch/x86/kernel/cpu/amd.c | 3 +-
arch/x86/kernel/kvmclock.c | 2 +-
arch/x86/kernel/sev-shared.c | 10 +
arch/x86/kernel/sev.c | 581 +++++++++++++++++--
arch/x86/mm/mem_encrypt.c | 4 +
arch/x86/mm/mem_encrypt_amd.c | 4 +
arch/x86/mm/mem_encrypt_identity.c | 7 +
drivers/virt/coco/sev-guest/sev-guest.c | 711 +++---------------------
arch/x86/Kconfig | 1 +
drivers/virt/coco/sev-guest/Kconfig | 3 -
17 files changed, 843 insertions(+), 764 deletions(-)
delete mode 100644 drivers/virt/coco/sev-guest/sev-guest.h

base-commit: 1613e604df0cd359cf2a7fbd9be7a0bcfacfabd0
--
2.34.1