netdev - Re: [PATCH bpf] cpumap: disable page_pool direct xdp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aJ5Ne4U2nLY5DmCL@861G6M3>
Date: Thu, 14 Aug 2025 15:56:27 -0500
From: Chris Arges <carges@...udflare.com>
To: Jesper Dangaard Brouer <hawk@...nel.org>
Cc: bpf@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
	dtatulea@...dia.com, Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <borkmann@...earbox.net>, netdev@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paolo Abeni <pabeni@...hat.com>, tariqt@...dia.com,
	memxor@...il.com, john.fastabend@...il.com,
	kernel-team@...udflare.com, yan@...udflare.com,
	jbrandeburg@...udflare.com, arzeznik@...udflare.com
Subject: Re: [PATCH bpf] cpumap: disable page_pool direct xdp_return need
 larger scope

On 2025-08-14 20:24:37, Jesper Dangaard Brouer wrote:
> When running an XDP bpf_prog on the remote CPU in cpumap code
> then we must disable the direct return optimization that
> xdp_return can perform for mem_type page_pool.  This optimization
> assumes code is still executing under RX-NAPI of the original
> receiving CPU, which isn't true on this remote CPU.
> 
> The cpumap code already disabled this via helpers
> xdp_set_return_frame_no_direct() and xdp_clear_return_frame_no_direct(),
> but the scope didn't include xdp_do_flush().
> 
> When doing XDP_REDIRECT towards e.g devmap this causes the
> function bq_xmit_all() to run with direct return optimization
> enabled. This can lead to hard to find bugs.  The issue
> only happens when bq_xmit_all() cannot ndo_xdp_xmit all
> frames and them frees them via xdp_return_frame_rx_napi().
> 
> Fix by expanding scope to include xdp_do_flush().
> 
> Fixes: 11941f8a8536 ("bpf: cpumap: Implement generic cpumap")
> Found-by: Dragos Tatulea <dtatulea@...dia.com>
> Reported-by: Chris Arges <carges@...udflare.com>
> Signed-off-by: Jesper Dangaard Brouer <hawk@...nel.org>
> ---
>  kernel/bpf/cpumap.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index b2b7b8ec2c2a..c46360b27871 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -186,7 +186,6 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
>  	struct xdp_buff xdp;
>  	int i, nframes = 0;
>  
> -	xdp_set_return_frame_no_direct();
>  	xdp.rxq = &rxq;
>  
>  	for (i = 0; i < n; i++) {
> @@ -231,7 +230,6 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
>  		}
>  	}
>  
> -	xdp_clear_return_frame_no_direct();
>  	stats->pass += nframes;
>  
>  	return nframes;
> @@ -255,6 +253,7 @@ static void cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
>  
>  	rcu_read_lock();
>  	bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
> +	xdp_set_return_frame_no_direct();
>  
>  	ret->xdp_n = cpu_map_bpf_prog_run_xdp(rcpu, frames, ret->xdp_n, stats);
>  	if (unlikely(ret->skb_n))
> @@ -264,6 +263,7 @@ static void cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
>  	if (stats->redirect)
>  		xdp_do_flush();
>  
> +	xdp_clear_return_frame_no_direct();
>  	bpf_net_ctx_clear(bpf_net_ctx);
>  	rcu_read_unlock();
>  
> 
>

FWIW, I tested this patch and could no longer reproduce the original issue.

Tested-By: Chris Arges <carges@...udflare.com>

--chris