From: John Hubbard <jhubbard@nvidia.com>
Date: Mon, 25 May 2020 23:22:06 -0700
Subject: KVM: SVM: fix svn_pin_memory()'s use of get_user_pages_fast()
Git-commit: 78824fabc72e5e37d51e6e567fde70a4fc41a6d7
Patch-mainline: v5.9-rc1
References: bsc#1112178

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 <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Message-Id: <20200526062207.1360225-2-jhubbard@nvidia.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kvm/svm.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1780,7 +1780,8 @@ static struct page **sev_pin_memory(stru
 				    int write)
 {
 	struct kvm_sev_info *sev = &kvm->arch.sev_info;
-	unsigned long npages, npinned, size;
+	unsigned long npages, size;
+	int npinned;
 	unsigned long locked, lock_limit;
 	struct page **pages;
 	int first, last;
@@ -1797,6 +1798,9 @@ static struct page **sev_pin_memory(stru
 		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)