[PATCH] KVM: arm64: Fix potential leak in hyp_trace_buffer_alloc_bpages_backing

[Fuad Tabba]

Hi Vincent,

On Tue, 7 Jul 2026 at 17:50, Vincent Donnefort <vdonnefort at google.com> wrote:
>
> In the very unlikely event of a failure in __map_hyp, the allocated
> backing pages are leaked in hyp_trace_buffer_alloc_bpages_backing(). Fix
> this by freeing the pages on error.
>
> Fixes: 3aed038aac8d ("KVM: arm64: Add trace remote for the nVHE/pKVM hyp")
> Reported-by: Sashiko <sashiko-bot at kernel.org>
> Signed-off-by: Vincent Donnefort <vdonnefort at google.com>
>
> diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
> index 2411b4c32932..5fbbfd40376f 100644
> --- a/arch/arm64/kvm/hyp_trace.c
> +++ b/arch/arm64/kvm/hyp_trace.c
> @@ -160,6 +160,7 @@ static int hyp_trace_buffer_alloc_bpages_backing(struct hyp_trace_buffer *trace_
>         int nr_bpages = (PAGE_ALIGN(size) / PAGE_SIZE) + 1;
>         size_t backing_size;
>         void *start;
> +       int ret;
>
>         backing_size = PAGE_ALIGN(sizeof(struct simple_buffer_page) * nr_bpages *
>                                   num_possible_cpus());
> @@ -171,7 +172,11 @@ static int hyp_trace_buffer_alloc_bpages_backing(struct hyp_trace_buffer *trace_
>         trace_buffer->desc->bpages_backing_start = (unsigned long)start;
>         trace_buffer->desc->bpages_backing_size = backing_size;
>
> -       return __map_hyp(start, backing_size);
> +       ret = __map_hyp(start, backing_size);
> +       if (ret)
> +               free_pages_exact(start, backing_size);
> +
> +       return ret;
>  }

nit: would be a bit cleaner to do move the desc assignment to after
the check. Also, I think sashiko found another real bug, don't think
it's serious but worth fixing.

That said...

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

Cheers,
/fuad

>
>  static void hyp_trace_buffer_free_bpages_backing(struct hyp_trace_buffer *trace_buffer)
>
> base-commit: 8cdeaa50eae8dad34885515f62559ee83e7e8dda
> --
> 2.55.0.rc2.803.g1fd1e6609c-goog
>