[PATCH v4 16/17] KVM: arm64: Reject hyp trace descriptors with fewer than 3 pages

[Vincent Donnefort]

A trace descriptor with 0 nr_page_va allocates a 0-size bpages
backing region, which makes the ring buffer appear unloaded. Reject
descriptors with nr_page_va < 3 in hyp_trace_desc_is_valid() as this is
in any case the lower-limit for simple_ring_buffer.

Tested-by: Fuad Tabba <fuad.tabba at linux.dev>
Signed-off-by: Vincent Donnefort <vdonnefort at google.com>

diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
index 6e716295247a..96afa3d6de2f 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -189,6 +189,10 @@ static bool hyp_trace_desc_is_valid(struct hyp_trace_desc *desc, size_t desc_siz
 		if ((void *)rb_desc + struct_size(rb_desc, page_va, 0) > desc_end)
 			return false;
 
+		/* simple_ring_buffer_init_mm() expects at least 3 pages */
+		if (rb_desc->nr_page_va < 3)
+			return false;
+
 		/* Overflow desc? */
 		if ((void *)rb_desc + struct_size(rb_desc, page_va, rb_desc->nr_page_va) > desc_end)
 			return false;
-- 
2.55.0.508.g3f0d502094-goog