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Message-ID: <88185cd3-a9f4-68a8-9c34-2e72deaf3d8d@oracle.com>
Date: Fri, 3 Apr 2020 13:18:52 -0700
From: Krish Sadhukhan <krish.sadhukhan@...cle.com>
To: Ashish Kalra <Ashish.Kalra@....com>, pbonzini@...hat.com
Cc: tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
joro@...tes.org, bp@...e.de, thomas.lendacky@....com,
x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
rientjes@...gle.com, srutherford@...gle.com, luto@...nel.org,
brijesh.singh@....com
Subject: Re: [PATCH v6 09/14] KVM: x86: Introduce KVM_GET_PAGE_ENC_BITMAP
ioctl
On 3/29/20 11:22 PM, Ashish Kalra wrote:
> From: Brijesh Singh <Brijesh.Singh@....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.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
> 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 */
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