Re: [PATCH v6 09/14] KVM: x86: Introduce KVM_GET_PAGE_ENC_BITMAP ioctl
From: Krish Sadhukhan
Date: Mon Apr 06 2020 - 18:08:28 EST
On 4/3/20 1:47 PM, Ashish Kalra wrote:
On Fri, Apr 03, 2020 at 01:18:52PM -0700, Krish Sadhukhan wrote:
On 3/29/20 11:22 PM, Ashish Kalra wrote:
From: Brijesh Singh <Brijesh.Singh@xxxxxxx>
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@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
Cc: Joerg Roedel <joro@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
---
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,
ÂÂÂ ÂÂÂ set_page_enc_hc
ÂÂÂ ÂÂÂ get_page_enc_ioctl
};
These are named as per their usage. While the page_enc_status_hc is a
hypercall used by a guest to mark the page encryption bitmap, the other
ones are ioctl interfaces used by Qemu (or Qemu alternative) to get/set
the page encryption bitmaps, so these are named accordingly.
OK.
Please rename 'set_page_enc_hc' to 'set_page_enc_hypercall' to match
'patch_hypercall'.
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
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 ?
This is not checking for "num_pages", this is basically checking if
bmap->num_pages is not byte aligned.
+ unsigned char *bitmap_kernel = (unsigned char *)bitmap;
Just trying to understand why you need this extra variable instead of using
'bitmap' directly.
Makes the code much more readable/understandable.
+ 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 ?
As per the comments above, please note if n is not zero that means
bmap->num_pages is not byte aligned so we read the trailing bits
from the userspace and copy those bits as is. If n is zero, then
bmap->num_pages is correctly aligned and we copy all the bytes back.
Thanks,
Ashish
+ 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 */