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

[Fuad Tabba]

On Fri, 31 Jul 2026 at 15:36, Vincent Donnefort <vdonnefort at google.com> wrote:
>
> 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>

Reviewed-by: Fuad Tabba <fuad.tabba at linux.dev>

Cheers,
/fuad


>
> 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
>