On Thu, May 30, 2024 at 1:17 PM Pankaj Gupta <pankaj.gupta@xxxxxxx> wrote: > > From: Dov Murik <dovmurik@xxxxxxxxxxxxx> > > In SNP, the hashes page designated with a specific metadata entry > published in AmdSev OVMF. > > Therefore, if the user enabled kernel hashes (for measured direct boot), > QEMU should prepare the content of hashes table, and during the > processing of the metadata entry it copy the content into the designated > page and encrypt it. > > Note that in SNP (unlike SEV and SEV-ES) the measurements is done in > whole 4KB pages. Therefore QEMU zeros the whole page that includes the > hashes table, and fills in the kernel hashes area in that page, and then > encrypts the whole page. The rest of the page is reserved for SEV > launch secrets which are not usable anyway on SNP. > > If the user disabled kernel hashes, QEMU pre-validates the kernel hashes > page as a zero page. > > Signed-off-by: Dov Murik <dovmurik@xxxxxxxxxxxxx> > Signed-off-by: Michael Roth <michael.roth@xxxxxxx> > Signed-off-by: Pankaj Gupta <pankaj.gupta@xxxxxxx> > --- > include/hw/i386/pc.h | 2 ++ > target/i386/sev.c | 35 +++++++++++++++++++++++++++++++++++ > 2 files changed, 37 insertions(+) > > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h > index c653b8eeb2..ca7904ac2c 100644 > --- a/include/hw/i386/pc.h > +++ b/include/hw/i386/pc.h > @@ -172,6 +172,8 @@ typedef enum { > SEV_DESC_TYPE_SNP_SECRETS, > /* The section contains address that can be used as a CPUID page */ > SEV_DESC_TYPE_CPUID, > + /* The section contains the region for kernel hashes for measured direct boot */ > + SEV_DESC_TYPE_SNP_KERNEL_HASHES = 0x10, > > } ovmf_sev_metadata_desc_type; > > diff --git a/target/i386/sev.c b/target/i386/sev.c > index 1b29fdbc9a..1a78e98751 100644 > --- a/target/i386/sev.c > +++ b/target/i386/sev.c > @@ -145,6 +145,9 @@ struct SevSnpGuestState { > > struct kvm_sev_snp_launch_start kvm_start_conf; > struct kvm_sev_snp_launch_finish kvm_finish_conf; > + > + uint32_t kernel_hashes_offset; > + PaddedSevHashTable *kernel_hashes_data; > }; > > struct SevSnpGuestStateClass { > @@ -1187,6 +1190,23 @@ snp_launch_update_cpuid(uint32_t cpuid_addr, void *hva, uint32_t cpuid_len) > KVM_SEV_SNP_PAGE_TYPE_CPUID); > } > > +static int > +snp_launch_update_kernel_hashes(SevSnpGuestState *sev_snp, uint32_t addr, > + void *hva, uint32_t len) > +{ > + int type = KVM_SEV_SNP_PAGE_TYPE_ZERO; > + if (sev_snp->parent_obj.kernel_hashes) { > + assert(sev_snp->kernel_hashes_data); > + assert((sev_snp->kernel_hashes_offset + > + sizeof(*sev_snp->kernel_hashes_data)) <= len); > + memset(hva, 0, len); > + memcpy(hva + sev_snp->kernel_hashes_offset, sev_snp->kernel_hashes_data, > + sizeof(*sev_snp->kernel_hashes_data)); > + type = KVM_SEV_SNP_PAGE_TYPE_NORMAL; > + } > + return snp_launch_update_data(addr, hva, len, type); > +} > + > static int > snp_metadata_desc_to_page_type(int desc_type) > { > @@ -1223,6 +1243,9 @@ snp_populate_metadata_pages(SevSnpGuestState *sev_snp, > > if (type == KVM_SEV_SNP_PAGE_TYPE_CPUID) { > ret = snp_launch_update_cpuid(desc->base, hva, desc->len); > + } else if (desc->type == SEV_DESC_TYPE_SNP_KERNEL_HASHES) { > + ret = snp_launch_update_kernel_hashes(sev_snp, desc->base, hva, > + desc->len); > } else { > ret = snp_launch_update_data(desc->base, hva, desc->len, type); > } > @@ -1855,6 +1878,18 @@ bool sev_add_kernel_loader_hashes(SevKernelLoaderContext *ctx, Error **errp) > return false; > } > > + if (sev_snp_enabled()) { > + /* > + * SNP: Populate the hashes table in an area that later in > + * snp_launch_update_kernel_hashes() will be copied to the guest memory > + * and encrypted. > + */ > + SevSnpGuestState *sev_snp_guest = SEV_SNP_GUEST(sev_common); > + sev_snp_guest->kernel_hashes_offset = area->base & ~TARGET_PAGE_MASK; > + sev_snp_guest->kernel_hashes_data = g_new0(PaddedSevHashTable, 1); > + return build_kernel_loader_hashes(sev_snp_guest->kernel_hashes_data, ctx, errp); > + } This is effectively a new method: bool (*build_kernel_loader_hashes)(SevCommonState *sev_common, SevHashTableDescriptor *area, SevKernelLoaderContext *ctx, Error **errp); where the four lines above are the implementation for SNP and the code below is the implementation for sev-guest. Paolo > /* > * Populate the hashes table in the guest's memory at the OVMF-designated > * area for the SEV hashes table > -- > 2.34.1 >