Re: [PATCH v2 3/9] KVM: x86: Introduce KVM_GET_PAGE_ENC_BITMAP ioctl

Dov Murik
2020-12-06T11:05:19Z

On 01/12/2020 2:47, Ashish Kalra wrote:
> From: Brijesh Singh <brijesh.singh@amd.com>
>
> The ioctl can be used to retrieve page encryption bitmap for a given
> gfn range.
>
> 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.

I think you meant to say "Ensure that we only copy bmap->num_pages
*bits* in the userspace buffer". But maybe I'm missed something.

>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: x86@kernel.org
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
> Documentation/virt/kvm/api.rst | 27 +++++++++++++
> arch/x86/include/asm/kvm_host.h | 2 +
> arch/x86/kvm/svm/sev.c | 70 +++++++++++++++++++++++++++++++++
> arch/x86/kvm/svm/svm.c | 1 +
> arch/x86/kvm/svm/svm.h | 1 +
> arch/x86/kvm/x86.c | 12 ++++++
> include/uapi/linux/kvm.h | 12 ++++++
> 7 files changed, 125 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 70254eaa5229..ae410f4332ab 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -4671,6 +4671,33 @@ 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 the concept of private and shared pages. The private
> +pages are encrypted with the guest-specific key, while the shared pages 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 the userspace need to use SEV migration commands to transmit
> +the page.
> +
>
> 4.125 KVM_S390_PV_COMMAND
> -------------------------
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d035dc983a7a..8c2e40199ecb 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1284,6 +1284,8 @@ struct kvm_x86_ops {
> void (*msr_filter_changed)(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);
> };
>
> struct kvm_x86_nested_ops {
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 6b8bc1297f9c..a6586dd29767 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1014,6 +1014,76 @@ int svm_page_enc_status_hc(struct kvm *kvm, unsigned long gpa,
> return 0;
> }
>
> +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;
> + gfn_end = gfn_start + bmap->num_pages;
> +
> + sz = ALIGN(bmap->num_pages, BITS_PER_LONG) / BITS_PER_BYTE;
> + bitmap = kmalloc(sz, GFP_KERNEL);

Maybe use bitmap_alloc which accepts size in bits (and corresponding
bitmap_free)?

> + if (!bitmap)
> + return -ENOMEM;
> +
> + /* by default all pages are marked encrypted */
> + memset(bitmap, 0xff, sz);

Maybe use bitmap_fill to clarify the intent?

> +
> + 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;

Maybe clearer:

sz_bytes = BITS_TO_BYTES(bmap->num_pages);

> +
> + /*
> + * 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.
> + */

(see my comment on the commit message above.)

> +
> + if (n) {
> + unsigned char *bitmap_kernel = (unsigned char *)bitmap;
> + 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))
> + goto out;
> +
> + ret = 0;
> +out:
> + kfree(bitmap);
> + return ret;
> +}
> +
> int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
> {
> struct kvm_sev_cmd sev_cmd;
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 7122ea5f7c47..bff89cab3ed0 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4314,6 +4314,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> .msr_filter_changed = svm_msr_filter_changed,
>
> .page_enc_status_hc = svm_page_enc_status_hc,
> + .get_page_enc_bitmap = svm_get_page_enc_bitmap,
> };
>
> static struct kvm_x86_init_ops svm_init_ops __initdata = {
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 0103a23ca174..4ce73f1034b9 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -413,6 +413,7 @@ int nested_svm_exit_special(struct vcpu_svm *svm);
> void sync_nested_vmcb_control(struct vcpu_svm *svm);
> int svm_page_enc_status_hc(struct kvm *kvm, unsigned long gpa,
> unsigned long npages, unsigned long enc);
> +int svm_get_page_enc_bitmap(struct kvm *kvm, struct kvm_page_enc_bitmap *bmap);
>
> extern struct kvm_x86_nested_ops svm_nested_ops;
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 3afc78f18f69..d3cb95a4dd55 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5695,6 +5695,18 @@ long kvm_arch_vm_ioctl(struct file *filp,
> case KVM_X86_SET_MSR_FILTER:
> r = kvm_vm_ioctl_set_msr_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 886802b8ffba..d0b9171bdb03 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -532,6 +532,16 @@ 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;
> @@ -1563,6 +1573,8 @@ struct kvm_pv_cmd {
> /* Available with KVM_CAP_DIRTY_LOG_RING */
> #define KVM_RESET_DIRTY_RINGS _IO(KVMIO, 0xc7)
>
> +#define KVM_GET_PAGE_ENC_BITMAP _IOW(KVMIO, 0xc6, struct kvm_page_enc_bitmap)

I see that kvm/next already defines ioctls numbered 0xc6 and 0xc7.
Wouldn't these new ioctls (KVM_GET_PAGE_ENC_BITMAP,
KVM_SET_PAGE_ENC_BITMAP) collide?

> +
> /* Secure Encrypted Virtualization command */
> enum sev_cmd_id {
> /* Guest initialization commands */
>

-Dov