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Date: Sun, 29 Oct 2023 16:55:39 -0600
From: Daniel Xu <dxu@...uu.xyz>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Jesper Dangaard Brouer <hawk@...nel.org>,
Steffen Klassert <steffen.klassert@...unet.com>, Alexei Starovoitov <ast@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Daniel Borkmann <daniel@...earbox.net>,
Jakub Kicinski <kuba@...nel.org>, Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>, John Fastabend <john.fastabend@...il.com>,
Eric Dumazet <edumazet@...gle.com>, antony.antony@...unet.com, LKML <linux-kernel@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, devel@...ux-ipsec.org
Subject: Re: [RFC bpf-next 1/6] bpf: xfrm: Add bpf_xdp_get_xfrm_state() kfunc
Hi Alexei,
On Sat, Oct 28, 2023 at 04:49:45PM -0700, Alexei Starovoitov wrote:
> On Fri, Oct 27, 2023 at 11:46 AM Daniel Xu <dxu@...uu.xyz> wrote:
> >
> > This commit adds an unstable kfunc helper to access internal xfrm_state
> > associated with an SA. This is intended to be used for the upcoming
> > IPsec pcpu work to assign special pcpu SAs to a particular CPU. In other
> > words: for custom software RSS.
> >
> > That being said, the function that this kfunc wraps is fairly generic
> > and used for a lot of xfrm tasks. I'm sure people will find uses
> > elsewhere over time.
> >
> > Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> > ---
> > include/net/xfrm.h | 9 ++++
> > net/xfrm/Makefile | 1 +
> > net/xfrm/xfrm_policy.c | 2 +
> > net/xfrm/xfrm_state_bpf.c | 105 ++++++++++++++++++++++++++++++++++++++
> > 4 files changed, 117 insertions(+)
> > create mode 100644 net/xfrm/xfrm_state_bpf.c
> >
> > diff --git a/include/net/xfrm.h b/include/net/xfrm.h
> > index 98d7aa78adda..ab4cf66480f3 100644
> > --- a/include/net/xfrm.h
> > +++ b/include/net/xfrm.h
> > @@ -2188,4 +2188,13 @@ static inline int register_xfrm_interface_bpf(void)
> >
> > #endif
> >
> > +#if IS_ENABLED(CONFIG_DEBUG_INFO_BTF)
> > +int register_xfrm_state_bpf(void);
> > +#else
> > +static inline int register_xfrm_state_bpf(void)
> > +{
> > + return 0;
> > +}
> > +#endif
> > +
> > #endif /* _NET_XFRM_H */
> > diff --git a/net/xfrm/Makefile b/net/xfrm/Makefile
> > index cd47f88921f5..547cec77ba03 100644
> > --- a/net/xfrm/Makefile
> > +++ b/net/xfrm/Makefile
> > @@ -21,3 +21,4 @@ obj-$(CONFIG_XFRM_USER_COMPAT) += xfrm_compat.o
> > obj-$(CONFIG_XFRM_IPCOMP) += xfrm_ipcomp.o
> > obj-$(CONFIG_XFRM_INTERFACE) += xfrm_interface.o
> > obj-$(CONFIG_XFRM_ESPINTCP) += espintcp.o
> > +obj-$(CONFIG_DEBUG_INFO_BTF) += xfrm_state_bpf.o
> > diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> > index 5cdd3bca3637..62e64fa7ae5c 100644
> > --- a/net/xfrm/xfrm_policy.c
> > +++ b/net/xfrm/xfrm_policy.c
> > @@ -4267,6 +4267,8 @@ void __init xfrm_init(void)
> > #ifdef CONFIG_XFRM_ESPINTCP
> > espintcp_init();
> > #endif
> > +
> > + register_xfrm_state_bpf();
> > }
> >
> > #ifdef CONFIG_AUDITSYSCALL
> > diff --git a/net/xfrm/xfrm_state_bpf.c b/net/xfrm/xfrm_state_bpf.c
> > new file mode 100644
> > index 000000000000..a73a17a6497b
> > --- /dev/null
> > +++ b/net/xfrm/xfrm_state_bpf.c
> > @@ -0,0 +1,105 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/* Unstable XFRM state BPF helpers.
> > + *
> > + * Note that it is allowed to break compatibility for these functions since the
> > + * interface they are exposed through to BPF programs is explicitly unstable.
> > + */
> > +
> > +#include <linux/bpf.h>
> > +#include <linux/btf_ids.h>
> > +#include <net/xdp.h>
> > +#include <net/xfrm.h>
> > +
> > +/* bpf_xfrm_state_opts - Options for XFRM state lookup helpers
> > + *
> > + * Members:
> > + * @error - Out parameter, set for any errors encountered
> > + * Values:
> > + * -EINVAL - netns_id is less than -1
> > + * -EINVAL - Passed NULL for opts
> > + * -EINVAL - opts__sz isn't BPF_XFRM_STATE_OPTS_SZ
> > + * -ENONET - No network namespace found for netns_id
> > + * @netns_id - Specify the network namespace for lookup
> > + * Values:
> > + * BPF_F_CURRENT_NETNS (-1)
> > + * Use namespace associated with ctx
> > + * [0, S32_MAX]
> > + * Network Namespace ID
> > + * @mark - XFRM mark to match on
> > + * @daddr - Destination address to match on
> > + * @spi - Security parameter index to match on
> > + * @proto - L3 protocol to match on
> > + * @family - L3 protocol family to match on
> > + */
> > +struct bpf_xfrm_state_opts {
> > + s32 error;
> > + s32 netns_id;
> > + u32 mark;
> > + xfrm_address_t daddr;
> > + __be32 spi;
> > + u8 proto;
> > + u16 family;
> > +};
> > +
> > +enum {
> > + BPF_XFRM_STATE_OPTS_SZ = sizeof(struct bpf_xfrm_state_opts),
> > +};
> > +
> > +__diag_push();
> > +__diag_ignore_all("-Wmissing-prototypes",
> > + "Global functions as their definitions will be in xfrm_state BTF");
> > +
> > +/* bpf_xdp_get_xfrm_state - Get XFRM state
> > + *
> > + * Parameters:
> > + * @ctx - Pointer to ctx (xdp_md) in XDP program
> > + * Cannot be NULL
> > + * @opts - Options for lookup (documented above)
> > + * Cannot be NULL
> > + * @opts__sz - Length of the bpf_xfrm_state_opts structure
> > + * Must be BPF_XFRM_STATE_OPTS_SZ
> > + */
> > +__bpf_kfunc struct xfrm_state *
> > +bpf_xdp_get_xfrm_state(struct xdp_md *ctx, struct bpf_xfrm_state_opts *opts, u32 opts__sz)
> > +{
> > + struct xdp_buff *xdp = (struct xdp_buff *)ctx;
> > + struct net *net = dev_net(xdp->rxq->dev);
> > +
> > + if (!opts || opts__sz != BPF_XFRM_STATE_OPTS_SZ) {
> > + opts->error = -EINVAL;
> > + return NULL;
> > + }
> > +
> > + if (unlikely(opts->netns_id < BPF_F_CURRENT_NETNS)) {
> > + opts->error = -EINVAL;
> > + return NULL;
> > + }
> > +
> > + if (opts->netns_id >= 0) {
> > + net = get_net_ns_by_id(net, opts->netns_id);
> > + if (unlikely(!net)) {
> > + opts->error = -ENONET;
> > + return NULL;
> > + }
> > + }
> > +
> > + return xfrm_state_lookup(net, opts->mark, &opts->daddr, opts->spi,
> > + opts->proto, opts->family);
> > +}
>
> Patch 6 example does little to explain how this kfunc can be used.
> Cover letter sounds promising, but no code to demonstrate the result.
Part of the reason for that is this kfunc is intended to be used with a
not-yet-upstreamed xfrm patchset. The other is that the usage is quite
trivial. This is the code the experiments were run with:
https://github.com/danobi/xdp-tools/blob/e89a1c617aba3b50d990f779357d6ce2863ecb27/xdp-bench/xdp_redirect_cpumap.bpf.c#L385-L406
We intend to upstream that cpumap mode to xdp-tools as soon as the xfrm
patches are in. (Note the linked code is a little buggy but the
main idea is there).
Depending on your appetite for complex diagrams, I can also offer you a
sequence diagram that describes how everything fits together:
https://dxuuu.xyz/r/ipsec-pcpu.png
The TLDR is that all the magic comes from xfrm subsystem. This kfunc
just enables software RSS.
> The main issue is that this kfunc has to be KF_ACQUIRE,
> otherwise bpf prog will keep leaking xfrm_state.
> Plenty of red flags in this RFC.
Ack, will check on KF_ACQUIRE.
Thanks,
Daniel
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