[PATCH] KVM: pfncache: Fix uhva validity check in kvm_gpc_is_valid_len()

[phind.uet@gmail.com]

From: Nguyen Dinh Phi <phind.uet@gmail.com>

In kvm_gpc_is_valid_len(), if the GPA is an error GPA, the function uses
uhva to calculate the page offset. However, if uhva is invalid, its value
can still be page-aligned (for example, PAGE_OFFSET) and this function will
still return true.

An invalid uhva could lead to incorrect offset calculations and potentially
trigger a WARN_ON_ONCE in __kvm_gpc_refresh().

Fixing it by adding an additional check for uhva.

Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
Reported-by: syzbot+cde12433b6c56f55d9ed@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=cde12433b6c56f55d9ed

---
 virt/kvm/pfncache.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 728d2c1b488a..707ead0a096c 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -60,8 +60,16 @@ void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
 static bool kvm_gpc_is_valid_len(gpa_t gpa, unsigned long uhva,
 				 unsigned long len)
 {
-	unsigned long offset = kvm_is_error_gpa(gpa) ? offset_in_page(uhva) :
-						       offset_in_page(gpa);
+	unsigned long offset;
+
+	if (kvm_is_error_gpa(gpa)) {
+		if (kvm_is_error_hva(uhva))
+			return false;
+
+		offset = offset_in_page(uhva);
+	} else {
+		offset = offset_in_page(gpa);
+	}
 
 	/*
 	 * The cached access must fit within a single page. The 'len' argument
-- 
2.43.0