This patchset is also available at: https://github.com/amdese/linux/commits/snp-certs-v3 and is based on top of kvm/kvm-coco-queue (14cfaed7621d) v2 of these patches were previously submitted under: [PATCH v2 0/2] SEV-SNP: Add KVM support for SNP certificate fetching via KVM_EXIT_COCO https://lore.kernel.org/kvm/20241119133513.3612633-1-michael.roth@xxxxxxx/ Overview -------- The GHCB 2.0 specification defines 2 GHCB request types to allow SNP guests to send encrypted messages/requests to firmware: SNP Guest Requests and SNP Extended Guest Requests. These encrypted messages are used for things like servicing attestation requests issued by the guest. Implementing support for these is required to be fully GHCB-compliant. For the most part, KVM only needs to handle forwarding these requests to firmware (to be issued via the SNP_GUEST_REQUEST firmware command defined in the SEV-SNP Firmware ABI), and then forwarding the encrypted response to the guest. However, in the case of SNP Extended Guest Requests, the host is also able to provide the certificate data corresponding to the endorsement key used by firmware to sign attestation report requests. This certificate data is provided by userspace because: 1) It allows for different keys/key types to be used for each particular guest with requiring any sort of KVM API to configure the certificate table in advance on a per-guest basis. 2) It provides additional flexibility with how attestation requests might be handled during live migration where the certificate data for source/dest might be different. 3) It allows all synchronization between certificates and firmware/signing key updates to be handled purely by userspace rather than requiring some in-kernel mechanism to facilitate it. [1] To support fetching certificate data from userspace, a new KVM KVM_EXIT_SNP_REQ_CERTS exit type is used to fetch the data similarly to KVM_EXIT_MMIO/etc, with an associate KVM capability to detect/enable the exits depending on whether userspace has been configured to provide certificate data. [1] https://lore.kernel.org/kvm/ZS614OSoritrE1d2@xxxxxxxxxx/ Testing ------- For testing this via QEMU, use the following tree: https://github.com/amdese/qemu/commits/snp-certs-rfc1-wip4 A basic command-line invocation for SNP with certificate data supplied would be: qemu-system-x86_64 -smp 32,maxcpus=255 -cpu EPYC-Milan-v2 -machine q35,confidential-guest-support=sev0,memory-backend=ram1 -object memory-backend-memfd,id=ram1,size=4G,share=true,reserve=false -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1,id-auth=,certs-path=/home/mroth/cert.blob -bios OVMF.fd Something like the following simple example can be used to simulate an exclusive lock being held on the certificate by management tools performing an update: #include <stdlib.h> #include <stdio.h> #define __USE_GNU #include <fcntl.h> #include <unistd.h> #include <errno.h> #include <stdbool.h> #include <sys/types.h> #include <sys/stat.h> int main(int argc, void **argv) { int ret, fd, i = 0; char *path = argv[1]; struct flock fl = { .l_whence = SEEK_SET, .l_start = 0, .l_len = 0, .l_type = F_WRLCK }; fd = open(path, O_RDWR); ret = fcntl(fd, F_OFD_SETLK, &fl); if (ret) { printf("error locking file, ret %d errno %d\n", ret, errno); return ret; } while (true) { i++; printf("now holding lock (%d seconds elapsed)...\n", i); usleep(1000 * 1000); } return 0; } The format of the certificate blob is defined in the GHCB 2.0 specification, but if it's not being parsed on the guest-side then random data will suffice for testing the KVM bits. Any feedback/review is appreciated. Thanks! -Mike Changes since v2: * As per discussion during PUCK, drop all the KVM_EXIT_COCO infrastructure since there are enough differences with TDX's quote generation to make unifying the 2 exits over-complicated for userspace, and the code-sharing we stand to gain from placing everything under the KVM_EXIT_COCO_* umbrella are of questionable benefit. * Update/simplify documentation as per the above. * Rebase/re-test on top of latest kvm-coco-queue Changes since v1: * Drop subtype-specific error codes. Instead use standard error codes like ENOSPC/etc. and let KVM determine whether a particular error requires special handling for a particular KVM_EXIT_COCO subtype. (Sean) * Introduce special handling for EAGAIN for KVM_EXIT_COCO_REQ_CERTS such that the guest can be instructed to retry if userspace is temporarily unable to immediately lock/provide the certificate data. (Sean) * Move the 'ret' field of struct kvm_exit_coco to the top-level so all sub-types can propagate error codes the same way. * Add more clarifying details in KVM documentation about the suggested file-locking scheme to avoid races between certificate requests and updates to SNP firmware that might modify the endorsement key corresponding to the certificate data. Changes since splitting this off from v15 SNP KVM patchset: * Address clang-reported warnings regarding uninitialized variables * Address a memory leak of the request/response buffer pages, and refactor the code based on Sean's suggestions: https://lore.kernel.org/kvm/ZktbBRLXeOp9X6aH@xxxxxxxxxx/ * Fix SNP Extended Guest Request handling to only attempt to fetch certificates if handling MSG_REQ_REPORT (attestation) message types * Drop KVM_EXIT_VMGEXIT and introduce KVM_EXIT_COCO events instead * Refactor patch layout for easier handling/review ---------------------------------------------------------------- Michael Roth (1): KVM: Introduce KVM_EXIT_SNP_REQ_CERTS for SNP certificate-fetching Documentation/virt/kvm/api.rst | 93 +++++++++++++++++++++++++++++++++++++++++ arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/svm/sev.c | 43 ++++++++++++++++--- arch/x86/kvm/x86.c | 11 +++++ include/uapi/linux/kvm.h | 10 +++++ include/uapi/linux/sev-guest.h | 8 ++++ 6 files changed, 160 insertions(+), 6 deletions(-)
