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Ensure that we only copy bmap->num_pages bytes in the > userspace buffer, if bmap->num_pages is not byte aligned we read > the trailing bits from the userspace and copy those bits as is. > > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: "H. Peter Anvin" > Cc: Paolo Bonzini > Cc: "Radim Krčmář" > Cc: Joerg Roedel > Cc: Borislav Petkov > Cc: Tom Lendacky > Cc: x86@kernel.org > Cc: kvm@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Brijesh Singh > Signed-off-by: Ashish Kalra > --- > Documentation/virt/kvm/api.rst | 27 +++++++++++++ > arch/x86/include/asm/kvm_host.h | 2 + > arch/x86/kvm/svm.c | 71 +++++++++++++++++++++++++++++++++ > arch/x86/kvm/x86.c | 12 ++++++ > include/uapi/linux/kvm.h | 12 ++++++ > 5 files changed, 124 insertions(+) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index ebd383fba939..8ad800ebb54f 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -4648,6 +4648,33 @@ This ioctl resets VCPU registers and control structures according to > the clear cpu reset definition in the POP. However, the cpu is not put > into ESA mode. This reset is a superset of the initial reset. > > +4.125 KVM_GET_PAGE_ENC_BITMAP (vm ioctl) > +--------------------------------------- > + > +:Capability: basic > +:Architectures: x86 > +:Type: vm ioctl > +:Parameters: struct kvm_page_enc_bitmap (in/out) > +:Returns: 0 on success, -1 on error > + > +/* for KVM_GET_PAGE_ENC_BITMAP */ > +struct kvm_page_enc_bitmap { > + __u64 start_gfn; > + __u64 num_pages; > + union { > + void __user *enc_bitmap; /* one bit per page */ > + __u64 padding2; > + }; > +}; > + > +The encrypted VMs have concept of private and shared pages. The private > +page is encrypted with the guest-specific key, while shared page may > +be encrypted with the hypervisor key. The KVM_GET_PAGE_ENC_BITMAP can > +be used to get the bitmap indicating whether the guest page is private > +or shared. The bitmap can be used during the guest migration, if the page > +is private then userspace need to use SEV migration commands to transmit > +the page. > + > > 5. The kvm_run structure > ======================== > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 90718fa3db47..27e43e3ec9d8 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1269,6 +1269,8 @@ struct kvm_x86_ops { > int (*enable_direct_tlbflush)(struct kvm_vcpu *vcpu); > int (*page_enc_status_hc)(struct kvm *kvm, unsigned long gpa, > unsigned long sz, unsigned long mode); > + int (*get_page_enc_bitmap)(struct kvm *kvm, > + struct kvm_page_enc_bitmap *bmap); Looking back at the previous patch, it seems that these two are basically the setter/getter action for page encryption, though one is implemented as a hypercall while the other as an ioctl. If we consider the setter/getter aspect, isn't it better to have some sort of symmetry in the naming of the ops ? For example,         set_page_enc_hc         get_page_enc_ioctl > }; > > struct kvm_arch_async_pf { > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > index 1d8beaf1bceb..bae783cd396a 100644 > --- a/arch/x86/kvm/svm.c > +++ b/arch/x86/kvm/svm.c > @@ -7686,6 +7686,76 @@ static int svm_page_enc_status_hc(struct kvm *kvm, unsigned long gpa, > return ret; > } > > +static int svm_get_page_enc_bitmap(struct kvm *kvm, > + struct kvm_page_enc_bitmap *bmap) > +{ > + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info; > + unsigned long gfn_start, gfn_end; > + unsigned long sz, i, sz_bytes; > + unsigned long *bitmap; > + int ret, n; > + > + if (!sev_guest(kvm)) > + return -ENOTTY; > + > + gfn_start = bmap->start_gfn; What if bmap->start_gfn is junk ? > + gfn_end = gfn_start + bmap->num_pages; > + > + sz = ALIGN(bmap->num_pages, BITS_PER_LONG) / BITS_PER_BYTE; > + bitmap = kmalloc(sz, GFP_KERNEL); > + if (!bitmap) > + return -ENOMEM; > + > + /* by default all pages are marked encrypted */ > + memset(bitmap, 0xff, sz); > + > + mutex_lock(&kvm->lock); > + if (sev->page_enc_bmap) { > + i = gfn_start; > + for_each_clear_bit_from(i, sev->page_enc_bmap, > + min(sev->page_enc_bmap_size, gfn_end)) > + clear_bit(i - gfn_start, bitmap); > + } > + mutex_unlock(&kvm->lock); > + > + ret = -EFAULT; > + > + n = bmap->num_pages % BITS_PER_BYTE; > + sz_bytes = ALIGN(bmap->num_pages, BITS_PER_BYTE) / BITS_PER_BYTE; > + > + /* > + * Return the correct bitmap as per the number of pages being > + * requested by the user. Ensure that we only copy bmap->num_pages > + * bytes in the userspace buffer, if bmap->num_pages is not byte > + * aligned we read the trailing bits from the userspace and copy > + * those bits as is. > + */ > + > + if (n) { Is it better to check for 'num_pages' at the beginning of the function rather than coming this far if bmap->num_pages is zero ? > + unsigned char *bitmap_kernel = (unsigned char *)bitmap; Just trying to understand why you need this extra variable instead of using 'bitmap' directly. > + unsigned char bitmap_user; > + unsigned long offset, mask; > + > + offset = bmap->num_pages / BITS_PER_BYTE; > + if (copy_from_user(&bitmap_user, bmap->enc_bitmap + offset, > + sizeof(unsigned char))) > + goto out; > + > + mask = GENMASK(n - 1, 0); > + bitmap_user &= ~mask; > + bitmap_kernel[offset] &= mask; > + bitmap_kernel[offset] |= bitmap_user; > + } > + > + if (copy_to_user(bmap->enc_bitmap, bitmap, sz_bytes)) If 'n' is zero, we are still copying stuff back to the user. Is that what is expected from userland ? Another point. Since copy_from_user() was done in the caller, isn't it better to move this to the caller to keep a symmetry ? > + goto out; > + > + ret = 0; > +out: > + kfree(bitmap); > + return ret; > +} > + > static int svm_mem_enc_op(struct kvm *kvm, void __user *argp) > { > struct kvm_sev_cmd sev_cmd; > @@ -8090,6 +8160,7 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = { > .apic_init_signal_blocked = svm_apic_init_signal_blocked, > > .page_enc_status_hc = svm_page_enc_status_hc, > + .get_page_enc_bitmap = svm_get_page_enc_bitmap, > }; > > static int __init svm_init(void) > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 68428eef2dde..3c3fea4e20b5 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -5226,6 +5226,18 @@ long kvm_arch_vm_ioctl(struct file *filp, > case KVM_SET_PMU_EVENT_FILTER: > r = kvm_vm_ioctl_set_pmu_event_filter(kvm, argp); > break; > + case KVM_GET_PAGE_ENC_BITMAP: { > + struct kvm_page_enc_bitmap bitmap; > + > + r = -EFAULT; > + if (copy_from_user(&bitmap, argp, sizeof(bitmap))) > + goto out; > + > + r = -ENOTTY; > + if (kvm_x86_ops->get_page_enc_bitmap) > + r = kvm_x86_ops->get_page_enc_bitmap(kvm, &bitmap); > + break; > + } > default: > r = -ENOTTY; > } > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 4e80c57a3182..db1ebf85e177 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -500,6 +500,16 @@ struct kvm_dirty_log { > }; > }; > > +/* for KVM_GET_PAGE_ENC_BITMAP */ > +struct kvm_page_enc_bitmap { > + __u64 start_gfn; > + __u64 num_pages; > + union { > + void __user *enc_bitmap; /* one bit per page */ > + __u64 padding2; > + }; > +}; > + > /* for KVM_CLEAR_DIRTY_LOG */ > struct kvm_clear_dirty_log { > __u32 slot; > @@ -1478,6 +1488,8 @@ struct kvm_enc_region { > #define KVM_S390_NORMAL_RESET _IO(KVMIO, 0xc3) > #define KVM_S390_CLEAR_RESET _IO(KVMIO, 0xc4) > > +#define KVM_GET_PAGE_ENC_BITMAP _IOW(KVMIO, 0xc5, struct kvm_page_enc_bitmap) > + > /* Secure Encrypted Virtualization command */ > enum sev_cmd_id { > /* Guest initialization commands */