linux-kernel - Re: [PATCH bpf] xdp: use trusted arguments in XDP hints kfuncs

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Message-ID: <a05a4ac2-40c8-da67-6727-b9844930386e@redhat.com>
Date:   Tue, 11 Jul 2023 16:21:41 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Larysa Zaremba <larysa.zaremba@...el.com>, bpf@...r.kernel.org,
        Stanislav Fomichev <sdf@...gle.com>
Cc:     brouer@...hat.com, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] xdp: use trusted arguments in XDP hints kfuncs


On 11/07/2023 12.59, Larysa Zaremba wrote:
> Currently, verifier does not reject XDP programs that pass NULL pointer to
> hints functions. At the same time, this case is not handled in any driver
> implementation (including veth). For example, changing
> 
> bpf_xdp_metadata_rx_timestamp(ctx, &timestamp);
> 
> to
> 
> bpf_xdp_metadata_rx_timestamp(ctx, NULL);
> 
> in xdp_metadata test successfully crashes the system.
> 
> Add KF_TRUSTED_ARGS flag to hints kfunc definitions, so driver code
> does not have to worry about getting invalid pointers.
> 

Looks good to me, assuming this means verifier will reject BPF-prog's 
supplying NULL.

Acked-by: Jesper Dangaard Brouer <hawk@...nel.org>

> Fixes: 3d76a4d3d4e5 ("bpf: XDP metadata RX kfuncs")
> Reported-by: Stanislav Fomichev <sdf@...gle.com>
> Closes: https://lore.kernel.org/bpf/ZKWo0BbpLfkZHbyE@google.com/
> Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> ---
>   net/core/xdp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 41e5ca8643ec..8362130bf085 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -741,7 +741,7 @@ __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash,
>   __diag_pop();
>   
>   BTF_SET8_START(xdp_metadata_kfunc_ids)
> -#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, 0)
> +#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, KF_TRUSTED_ARGS)
>   XDP_METADATA_KFUNC_xxx
>   #undef XDP_METADATA_KFUNC
>   BTF_SET8_END(xdp_metadata_kfunc_ids)