[RFC 06/16] KVM: Use GUP instead of copy_from/to_user() to access guest memory

Kirill A. Shutemov
2020-05-22T12:52:32Z

New helpers copy_from_guest()/copy_to_guest() to be used if KVM memory
protection feature is enabled.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
include/linux/kvm_host.h | 4 +++
virt/kvm/kvm_main.c | 78 ++++++++++++++++++++++++++++++++++------
2 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 131cc1527d68..bd0bb600f610 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -503,6 +503,7 @@ struct kvm {
struct srcu_struct srcu;
struct srcu_struct irq_srcu;
pid_t userspace_pid;
+ bool mem_protected;
};

#define kvm_err(fmt, ...) \
@@ -727,6 +728,9 @@ void kvm_set_pfn_dirty(kvm_pfn_t pfn);
void kvm_set_pfn_accessed(kvm_pfn_t pfn);
void kvm_get_pfn(kvm_pfn_t pfn);

+int copy_from_guest(void *data, unsigned long hva, int len);
+int copy_to_guest(unsigned long hva, const void *data, int len);
+
void kvm_release_pfn(kvm_pfn_t pfn, bool dirty, struct gfn_to_pfn_cache *cache);
int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
int len);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 731c1e517716..033471f71dae 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2248,8 +2248,48 @@ static int next_segment(unsigned long len, int offset)
return len;
}

+int copy_from_guest(void *data, unsigned long hva, int len)
+{
+ int offset = offset_in_page(hva);
+ struct page *page;
+ int npages, seg;
+
+ while ((seg = next_segment(len, offset)) != 0) {
+ npages = get_user_pages_unlocked(hva, 1, &page, 0);
+ if (npages != 1)
+ return -EFAULT;
+ memcpy(data, page_address(page) + offset, seg);
+ put_page(page);
+ len -= seg;
+ hva += seg;
+ offset = 0;
+ }
+
+ return 0;
+}
+
+int copy_to_guest(unsigned long hva, const void *data, int len)
+{
+ int offset = offset_in_page(hva);
+ struct page *page;
+ int npages, seg;
+
+ while ((seg = next_segment(len, offset)) != 0) {
+ npages = get_user_pages_unlocked(hva, 1, &page, FOLL_WRITE);
+ if (npages != 1)
+ return -EFAULT;
+ memcpy(page_address(page) + offset, data, seg);
+ put_page(page);
+ len -= seg;
+ hva += seg;
+ offset = 0;
+ }
+ return 0;
+}
+
static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
- void *data, int offset, int len)
+ void *data, int offset, int len,
+ bool protected)
{
int r;
unsigned long addr;
@@ -2257,7 +2297,10 @@ static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
if (kvm_is_error_hva(addr))
return -EFAULT;
- r = __copy_from_user(data, (void __user *)addr + offset, len);
+ if (protected)
+ r = copy_from_guest(data, addr + offset, len);
+ else
+ r = __copy_from_user(data, (void __user *)addr + offset, len);
if (r)
return -EFAULT;
return 0;
@@ -2268,7 +2311,8 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
{
struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);

- return __kvm_read_guest_page(slot, gfn, data, offset, len);
+ return __kvm_read_guest_page(slot, gfn, data, offset, len,
+ kvm->mem_protected);
}
EXPORT_SYMBOL_GPL(kvm_read_guest_page);

@@ -2277,7 +2321,8 @@ int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data,
{
struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);

- return __kvm_read_guest_page(slot, gfn, data, offset, len);
+ return __kvm_read_guest_page(slot, gfn, data, offset, len,
+ vcpu->kvm->mem_protected);
}
EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_page);

@@ -2350,7 +2395,8 @@ int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa,
EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_atomic);

static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
- const void *data, int offset, int len)
+ const void *data, int offset, int len,
+ bool protected)
{
int r;
unsigned long addr;
@@ -2358,7 +2404,11 @@ static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
addr = gfn_to_hva_memslot(memslot, gfn);
if (kvm_is_error_hva(addr))
return -EFAULT;
- r = __copy_to_user((void __user *)addr + offset, data, len);
+
+ if (protected)
+ r = copy_to_guest(addr + offset, data, len);
+ else
+ r = __copy_to_user((void __user *)addr + offset, data, len);
if (r)
return -EFAULT;
mark_page_dirty_in_slot(memslot, gfn);
@@ -2370,7 +2420,8 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn,
{
struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);

- return __kvm_write_guest_page(slot, gfn, data, offset, len);
+ return __kvm_write_guest_page(slot, gfn, data, offset, len,
+ kvm->mem_protected);
}
EXPORT_SYMBOL_GPL(kvm_write_guest_page);

@@ -2379,7 +2430,8 @@ int kvm_vcpu_write_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn,
{
struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);

- return __kvm_write_guest_page(slot, gfn, data, offset, len);
+ return __kvm_write_guest_page(slot, gfn, data, offset, len,
+ vcpu->kvm->mem_protected);
}
EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest_page);

@@ -2495,7 +2547,10 @@ int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
if (unlikely(!ghc->memslot))
return kvm_write_guest(kvm, gpa, data, len);

- r = __copy_to_user((void __user *)ghc->hva + offset, data, len);
+ if (kvm->mem_protected)
+ r = copy_to_guest(ghc->hva + offset, data, len);
+ else
+ r = __copy_to_user((void __user *)ghc->hva + offset, data, len);
if (r)
return -EFAULT;
mark_page_dirty_in_slot(ghc->memslot, gpa >> PAGE_SHIFT);
@@ -2530,7 +2585,10 @@ int kvm_read_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
if (unlikely(!ghc->memslot))
return kvm_read_guest(kvm, ghc->gpa, data, len);

- r = __copy_from_user(data, (void __user *)ghc->hva, len);
+ if (kvm->mem_protected)
+ r = copy_from_guest(data, ghc->hva, len);
+ else
+ r = __copy_from_user(data, (void __user *)ghc->hva, len);
if (r)
return -EFAULT;

--
2.26.2