KVM: SVM: fix svn_pin_memory()'s use of get_user_pages_fast()

There are two problems in svn_pin_memory():

1) The return value of get_user_pages_fast() is stored in an
unsigned long, although the declared return value is of type int.
This will not cause any symptoms, but it is misleading.
Fix this by changing the type of npinned to "int".

2) The number of pages passed into get_user_pages_fast() is stored
in an unsigned long, even though get_user_pages_fast() accepts an
int. This means that it is possible to silently overflow the number
of pages.

Fix this by adding a WARN_ON_ONCE() and an early error return. The
npages variable is left as an unsigned long for convenience in
checking for overflow.

Fixes: 89c505809052 ("KVM: SVM: Add support for KVM_SEV_LAUNCH_UPDATE_DATA command")
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Vitaly Kuznetsov <[email protected]>
Cc: Wanpeng Li <[email protected]>
Cc: Jim Mattson <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: John Hubbard <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 5573a97f1520..ceeee4bb6150 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -313,7 +313,8 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
 				    int write)
 {
 	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
-	unsigned long npages, npinned, size;
+	unsigned long npages, size;
+	int npinned;
 	unsigned long locked, lock_limit;
 	struct page **pages;
 	unsigned long first, last;
@@ -333,6 +334,9 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
 		return NULL;
 	}
 
+	if (WARN_ON_ONCE(npages > INT_MAX))
+		return NULL;
+
 	/* Avoid using vmalloc for smaller buffers. */
 	size = npages * sizeof(struct page *);
 	if (size > PAGE_SIZE)