* Tom Lendacky (thomas.lendacky@xxxxxxx) wrote: > On 9/18/20 5:00 AM, Dr. David Alan Gilbert wrote: > > * Tom Lendacky (thomas.lendacky@xxxxxxx) wrote: > > > On 9/17/20 12:28 PM, Dr. David Alan Gilbert wrote: > > > > * Tom Lendacky (thomas.lendacky@xxxxxxx) wrote: > > > > > From: Tom Lendacky <thomas.lendacky@xxxxxxx> > > > > > > > > > > This patch series provides support for launching an SEV-ES guest. > > > > > > > > > > Secure Encrypted Virtualization - Encrypted State (SEV-ES) expands on the > > > > > SEV support to protect the guest register state from the hypervisor. See > > > > > "AMD64 Architecture Programmer's Manual Volume 2: System Programming", > > > > > section "15.35 Encrypted State (SEV-ES)" [1]. > > > > > > > > > > In order to allow a hypervisor to perform functions on behalf of a guest, > > > > > there is architectural support for notifying a guest's operating system > > > > > when certain types of VMEXITs are about to occur. This allows the guest to > > > > > selectively share information with the hypervisor to satisfy the requested > > > > > function. The notification is performed using a new exception, the VMM > > > > > Communication exception (#VC). The information is shared through the > > > > > Guest-Hypervisor Communication Block (GHCB) using the VMGEXIT instruction. > > > > > The GHCB format and the protocol for using it is documented in "SEV-ES > > > > > Guest-Hypervisor Communication Block Standardization" [2]. > > > > > > > > > > The main areas of the Qemu code that are updated to support SEV-ES are > > > > > around the SEV guest launch process and AP booting in order to support > > > > > booting multiple vCPUs. > > > > > > > > > > There are no new command line switches required. Instead, the desire for > > > > > SEV-ES is presented using the SEV policy object. Bit 2 of the SEV policy > > > > > object indicates that SEV-ES is required. > > > > > > > > > > The SEV launch process is updated in two ways. The first is that a the > > > > > KVM_SEV_ES_INIT ioctl is used to initialize the guest instead of the > > > > > standard KVM_SEV_INIT ioctl. The second is that before the SEV launch > > > > > measurement is calculated, the LAUNCH_UPDATE_VMSA SEV API is invoked for > > > > > each vCPU that Qemu has created. Once the LAUNCH_UPDATE_VMSA API has been > > > > > invoked, no direct changes to the guest register state can be made. > > > > > > > > > > AP booting poses some interesting challenges. The INIT-SIPI-SIPI sequence > > > > > is typically used to boot the APs. However, the hypervisor is not allowed > > > > > to update the guest registers. For the APs, the reset vector must be known > > > > > in advance. An OVMF method to provide a known reset vector address exists > > > > > by providing an SEV information block, identified by UUID, near the end of > > > > > the firmware [3]. OVMF will program the jump to the actual reset vector in > > > > > this area of memory. Since the memory location is known in advance, an AP > > > > > can be created with the known reset vector address as its starting CS:IP. > > > > > The GHCB document [2] talks about how SMP booting under SEV-ES is > > > > > performed. SEV-ES also requires the use of the in-kernel irqchip support > > > > > in order to minimize the changes required to Qemu to support AP booting. > > > > > > > > Some random thoughts: > > > > a) Is there something that explicitly disallows SMM? > > > > > > There isn't currently. Is there a way to know early on that SMM is enabled? > > > Could I just call x86_machine_is_smm_enabled() to check that? > > > > > > > b) I think all the interfaces you're using are already defined in > > > > Linux header files - even if the code to implement them isn't actually > > > > upstream in the kernel yet (the launch_update in particular) - we > > > > normally wait for the kernel interface to be accepted before taking the > > > > QEMU patches, but if the constants are in the headers already I'm not > > > > sure what the rule is. > > > > > > Correct, everything was already present from a Linux header perspective. > > > > > > > c) What happens if QEMU reads the register values from the state if > > > > the guest is paused - does it just see junk? I'm just wondering if you > > > > need to add checks in places it might try to. > > > > > > I thought about what to do about calls to read the registers once the guest > > > state has become encrypted. I think it would take a lot of changes to make > > > Qemu "protected state aware" for what I see as little gain. Qemu is likely > > > to see a lot of zeroes or actual register values from the GHCB protocol for > > > previous VMGEXITs that took place. > > > > Yep, that's fair enough - I was curious if we'll hit anything > > accidentally still reading it. > > > > How does SEV-ES interact with the 'NODBG' flag of the guest policy - if > > that's 0, and 'debugging of the guest' is allowed, what can you actually > > do? > > The SEV-ES KVM patches will disallow debugging of the guest, or at least > setting breakpoints using the debug registers. Gdb can still break in, but > you wont get anything reasonable with register dumps and memory dumps. > > The NODBG policy bit enables or disables the DBG_DECRYPT and DBG_ENCRYPT > APIs. So if the guest has allowed debugging, memory dumps could be done > using those APIs (for encrypted pages). Registers are a different story > because you simply can't update from the hypervisor side under SEV-ES. > > Under SEV you could do actual debugging if the support was developed and in > place. Thanks for the explanation - it might be interesting to wire the DBG_DECRYPT support up to dump/dump.c for doing full guest memory dumps - if the policy has it enabled. Dave > Thanks, > Tom > > > > > Dave > > > > > Thanks, > > > Tom > > > > > > > > > > > Dave > > > > > > > > > [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.amd.com%2Fsystem%2Ffiles%2FTechDocs%2F24593.pdf&data=02%7C01%7Cthomas.lendacky%40amd.com%7Cecf88d6f7bd0494d1b0e08d85bb9c19b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637360201727448609&sdata=e6CbpjDDvCUG2q9pk6OSsty0QB5HuhueVAM4t8iygT8%3D&reserved=0 > > > > > [2] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdeveloper.amd.com%2Fwp-content%2Fresources%2F56421.pdf&data=02%7C01%7Cthomas.lendacky%40amd.com%7Cecf88d6f7bd0494d1b0e08d85bb9c19b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637360201727448609&sdata=%2FUzJB5K%2F8rOMF%2B%2BVPXjg%2BJBLgD4uLW6U82Wvf8pXq%2BA%3D&reserved=0 > > > > > [3] 30937f2f98c4 ("OvmfPkg: Use the SEV-ES work area for the SEV-ES AP reset vector") > > > > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftianocore%2Fedk2%2Fcommit%2F30937f2f98c42496f2f143fe8374ae7f7e684847&data=02%7C01%7Cthomas.lendacky%40amd.com%7Cecf88d6f7bd0494d1b0e08d85bb9c19b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637360201727458605&sdata=0FmiYEdIEtDjw1VIGaeeRrto%2FZpvH1esIgE93gXyagM%3D&reserved=0 > > > > > > > > > > --- > > > > > > > > > > These patches are based on commit: > > > > > d0ed6a69d3 ("Update version for v5.1.0 release") > > > > > > > > > > (I tried basing on the latest Qemu commit, but I was having build issues > > > > > that level) > > > > > > > > > > A version of the tree can be found at: > > > > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FAMDESE%2Fqemu%2Ftree%2Fsev-es-v11&data=02%7C01%7Cthomas.lendacky%40amd.com%7Cecf88d6f7bd0494d1b0e08d85bb9c19b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637360201727458605&sdata=w1tfrMDgruZBDxNHgKLhpKtQ50Ua%2FMy9IfkSXfne2xg%3D&reserved=0 > > > > > > > > > > Changes since v2: > > > > > - Add in-kernel irqchip requirement for SEV-ES guests > > > > > > > > > > Changes since v1: > > > > > - Fixed checkpatch.pl errors/warnings > > > > > > > > > > Tom Lendacky (5): > > > > > sev/i386: Add initial support for SEV-ES > > > > > sev/i386: Require in-kernel irqchip support for SEV-ES guests > > > > > sev/i386: Allow AP booting under SEV-ES > > > > > sev/i386: Don't allow a system reset under an SEV-ES guest > > > > > sev/i386: Enable an SEV-ES guest based on SEV policy > > > > > > > > > > accel/kvm/kvm-all.c | 73 ++++++++++++++++++++++++++ > > > > > accel/stubs/kvm-stub.c | 5 ++ > > > > > hw/i386/pc_sysfw.c | 10 +++- > > > > > include/sysemu/cpus.h | 2 + > > > > > include/sysemu/hw_accel.h | 5 ++ > > > > > include/sysemu/kvm.h | 18 +++++++ > > > > > include/sysemu/sev.h | 3 ++ > > > > > softmmu/cpus.c | 5 ++ > > > > > softmmu/vl.c | 5 +- > > > > > target/i386/cpu.c | 1 + > > > > > target/i386/kvm.c | 2 + > > > > > target/i386/sev-stub.c | 5 ++ > > > > > target/i386/sev.c | 105 +++++++++++++++++++++++++++++++++++++- > > > > > target/i386/sev_i386.h | 1 + > > > > > 14 files changed, 236 insertions(+), 4 deletions(-) > > > > > > > > > > -- > > > > > 2.28.0 > > > > > > > > > -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK
