On 20.08.20 00:49, Jim Mattson wrote:
On Mon, Aug 3, 2020 at 2:14 PM Alexander Graf <graf@xxxxxxxxxx> wrote:
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -901,6 +901,13 @@ struct kvm_hv {
struct kvm_hv_syndbg hv_syndbg;
};
+struct msr_bitmap_range {
+ u32 flags;
+ u32 nmsrs;
+ u32 base;
+ unsigned long *bitmap;
+};
+
enum kvm_irqchip_mode {
KVM_IRQCHIP_NONE,
KVM_IRQCHIP_KERNEL, /* created with KVM_CREATE_IRQCHIP */
@@ -1005,6 +1012,9 @@ struct kvm_arch {
/* Deflect RDMSR and WRMSR to user space when they trigger a #GP */
bool user_space_msr_enabled;
+ struct msr_bitmap_range msr_allowlist_ranges[10];
Why 10? I think this is the only use of this constant, but a macro
would still be nice, especially since the number appears to be
arbitrary.
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 0780f97c1850..c33fb1d72d52 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -192,6 +192,21 @@ struct kvm_msr_list {
__u32 indices[0];
};
+#define KVM_MSR_ALLOW_READ (1 << 0)
+#define KVM_MSR_ALLOW_WRITE (1 << 1)
+
+/* Maximum size of the of the bitmap in bytes */
+#define KVM_MSR_ALLOWLIST_MAX_LEN 0x600
Wouldn't 0x400 be a more natural size, since both Intel and AMD MSR
permission bitmaps cover ranges of 8192 MSRs?
You can always make your bitmaps 0x400 :). I had to choose something
that limits our memory footprint, so that user space can't allocate
infinite amounts of memory.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e1139124350f..25e58ceb19de 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1472,6 +1472,38 @@ void kvm_enable_efer_bits(u64 mask)
}
EXPORT_SYMBOL_GPL(kvm_enable_efer_bits);
+static bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type)
In another thread, when I suggested that a function should return
bool, you said, "'I'm not a big fan of bool returning APIs unless they
have an "is" in their name.' This function doesn't have "is" in its
name. :-)
I've left this unanswered for way too long :). IMHO, passive is fine
too, as it implies an "is" in my brain. Or to put it differently:
bad: bool kvm_get_msr()
bad: bool kvm_get_msr_user_space()
good: bool kvm_msr_blocked()
good: bool kvm_msr_allowed()
good: bool is_kvm_msr_allowed()
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct msr_bitmap_range *ranges = kvm->arch.msr_allowlist_ranges;
+ u32 count = kvm->arch.msr_allowlist_ranges_count;
Shouldn't the read of kvm->arch.msr_allowlist_ranges_count be guarded
by the mutex, below?
+ u32 i;
+ bool r = false;
+
+ /* MSR allowlist not set up, allow everything */
+ if (!count)
+ return true;
+
+ /* Prevent collision with clear_msr_allowlist */
+ mutex_lock(&kvm->lock);
+
+ for (i = 0; i < count; i++) {
+ u32 start = ranges[i].base;
+ u32 end = start + ranges[i].nmsrs;
+ u32 flags = ranges[i].flags;
+ unsigned long *bitmap = ranges[i].bitmap;
+
+ if ((index >= start) && (index < end) && (flags & type)) {
+ r = !!test_bit(index - start, bitmap);
The !! seems gratuitous, since r is of type bool.
@@ -1483,6 +1515,9 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
{
struct msr_data msr;
+ if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_ALLOW_WRITE))
+ return -ENOENT;
Perhaps -EPERM is more appropriate here?
switch (index) {
case MSR_FS_BASE:
case MSR_GS_BASE:
@@ -1528,6 +1563,9 @@ int __kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data,
struct msr_data msr;
int ret;
+ if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_ALLOW_READ))
+ return -ENOENT;
...and here?
+static bool msr_range_overlaps(struct kvm *kvm, struct msr_bitmap_range *range)
Another bool function with no "is"? :-)
+{
+ struct msr_bitmap_range *ranges = kvm->arch.msr_allowlist_ranges;
+ u32 i, count = kvm->arch.msr_allowlist_ranges_count;
+ bool r = false;
+
+ for (i = 0; i < count; i++) {
+ u32 start = max(range->base, ranges[i].base);
+ u32 end = min(range->base + range->nmsrs,
+ ranges[i].base + ranges[i].nmsrs);
+
+ if ((start < end) && (range->flags & ranges[i].flags)) {
+ r = true;
+ break;
+ }
+ }
+
+ return r;
+}
This seems like an awkward constraint. Would it be possible to allow
overlapping ranges as long as the access types don't clash? So, for
example, could I specify an allow list for READ of MSRs 0-0x1ffff and
an allow list for WRITE of MSRs 0-0x1ffff? Actually, I don't see why
you have to prohibit overlapping ranges at all.
I tend to agree. Now that the order is obvious through the new API, we
no longer need to check for overlaps.
+static int kvm_vm_ioctl_clear_msr_allowlist(struct kvm *kvm)
+{
+ int i;
Nit: In earlier code, you use u32 for this index. (I'm actually a fan
of int, myself.)
I usually use int as well because it's easier to type, but doing signed
indexes is just so wrong on so many levels :). I'll fix them up too be
all u32.
Alex
Amazon Development Center Germany GmbH
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