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From: Alexander Lobakin <alexandr.lobakin@intel.com>
To: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>
Cc: "Alexander Lobakin" <alexandr.lobakin@intel.com>,
	"Larysa Zaremba" <larysa.zaremba@intel.com>,
	"Michal Swiatkowski" <michal.swiatkowski@linux.intel.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"Björn Töpel" <bjorn@kernel.org>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"Maciej Fijalkowski" <maciej.fijalkowski@intel.com>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	"Toke Hoiland-Jorgensen" <toke@redhat.com>,
	"Lorenzo Bianconi" <lorenzo@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Jesse Brandeburg" <jesse.brandeburg@intel.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Yajun Deng" <yajun.deng@linux.dev>,
	"Willem de Bruijn" <willemb@google.com>,
	bpf@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, xdp-hints@xdp-project.net
Subject: [xdp-hints] [PATCH RFC bpf-next 50/52] libbpf: introduce a couple memory access helpers
Date: Tue, 28 Jun 2022 21:48:10 +0200	[thread overview]
Message-ID: <20220628194812.1453059-51-alexandr.lobakin@intel.com> (raw)
In-Reply-To: <20220628194812.1453059-1-alexandr.lobakin@intel.com>

From: Larysa Zaremba <larysa.zaremba@intel.com>

In BPF programs, it is a common thing to declare that we're going
to do a memory access via such snippet:

	if (data + ETH_HLEN > data_end)
		// bail out

Offsets can be variable:

	if (VLAN_HLEN * vlan_count > SOME_ARBITRARY_MAX_OFFSET ||
	    ctx->data + VLAN_HLEN * vlan_count > data_end)
		//

Or even calculated from the end:

	if (ctx->data_end - ctx->data - ETH_FCS_LEN > SOME_ARB_MAX_OFF ||
	    ctx->data_end - ETH_FCS_LEN < ctx->data)
		//

As a bonus, LLVM sometimes has a hard time compiling sane C code
the way that it would pass the in-kernel verifier.
Add two new functions to sanitize memory accesses and get pointers
to the requested ranges: one taking an offset from the start and one
from the end (useful for metadata and different integrity check
headers). They are written in Asm, so the offset can be variable and
the code will pass the verifier. There are checks for the maximum
offset (backed by the original verifier value), going out of bounds
etc., so the pointer they return is ready to use (if it's
non-%NULL).
So now all is needed is:

	iphdr = bpf_access_mem(ctx->data, ctx->data_end, ETH_HLEN,
			       sizeof(*iphdr));
	if (!iphdr)
		// bail out

or

	some_meta_struct = bpf_access_mem_end(ctx->data_meta, ctx->data,
					      sizeof(*some_meta_struct),
					      sizeof(*some_meta_struct));
	if (!some_meta_struct)
		//

The Asm code was happily stolen from the Cilium project repo[0] and
then reworked.

[0] https://github.com/cilium/cilium/blob/master/bpf/include/bpf/ctx/xdp.h#L43

Suggested-by: Daniel Borkmann <daniel@iogearbox.net> # original helper
Suggested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
Co-developed-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
---
 tools/lib/bpf/bpf_helpers.h | 64 +++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index fb04eaf367f1..cd16e3c9cd85 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -285,4 +285,68 @@ enum libbpf_tristate {
 /* Helper macro to print out debug messages */
 #define bpf_printk(fmt, args...) ___bpf_pick_printk(args)(fmt, ##args)
 
+/* Max offset as per kernel verifier */
+#define MAX_PACKET_OFF		0xffff
+
+/**
+ * bpf_access_mem - sanitize memory access to a range
+ * @mem: start of the memory segment
+ * @mem_end: end of the memory segment
+ * @off: offset from the start of the memory segment
+ * @len: length of the range to give access to
+ *
+ * Verifies that the memory operations we want to perform are sane and within
+ * bounds and gives pointer to the requested range. The checks are done in Asm,
+ * so that it is safe to pass variable offset (verifier might reject such code
+ * written in plain C).
+ * The intended way of using it is as follows:
+ *
+ * iphdr = bpf_access_mem(ctx->data, ctx->data_end, ETH_HLEN, sizeof(*iphdr));
+ *
+ * Returns pointer to the beginning of the range or %NULL.
+ */
+static __always_inline void *
+bpf_access_mem(__u64 mem, __u64 mem_end, __u64 off, const __u64 len)
+{
+	void *ret;
+
+	asm volatile("r1 = %[start]\n\t"
+		     "r2 = %[end]\n\t"
+		     "r3 = %[offmax] - %[len]\n\t"
+		     "if %[off] > r3 goto +5\n\t"
+		     "r1 += %[off]\n\t"
+		     "%[ret] = r1\n\t"
+		     "r1 += %[len]\n\t"
+		     "if r1 > r2 goto +1\n\t"
+		     "goto +1\n\t"
+		     "%[ret] = %[null]\n\t"
+		     : [ret]"=r"(ret)
+		     : [start]"r"(mem), [end]"r"(mem_end), [off]"r"(off),
+		       [len]"ri"(len), [offmax]"i"(MAX_PACKET_OFF),
+		       [null]"i"(NULL)
+		     : "r1", "r2", "r3");
+
+	return ret;
+}
+
+/**
+ * bpf_access_mem_end - sanitize memory access to a range at the end of segment
+ * @mem: start of the memory segment
+ * @mem_end: end of the memory segment
+ * @offend: offset from the end of the memory segment
+ * @len: length of the range to give access to
+ *
+ * Version of bpf_access_mem() which performs all needed calculations to
+ * access a memory segment from the end. E.g., to access FCS (if provided):
+ *
+ * cp = bpf_access_mem_end(ctx->data, ctx->data_end, ETH_FCS_LEN, ETH_FCS_LEN);
+ *
+ * Returns pointer to the beginning of the range or %NULL.
+ */
+static __always_inline void *
+bpf_access_mem_end(__u64 mem, __u64 mem_end, __u64 offend, const __u64 len)
+{
+	return bpf_access_mem(mem, mem_end, mem_end - mem - offend, len);
+}
+
 #endif
-- 
2.36.1


  parent reply	other threads:[~2022-06-28 19:50 UTC|newest]

Thread overview: 98+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-28 19:47 [xdp-hints] [PATCH RFC bpf-next 00/52] bpf, xdp: introduce and use Generic Hints/metadata Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 01/52] libbpf: factor out BTF loading from load_module_btfs() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 02/52] libbpf: try to load vmlinux BTF from the kernel first Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 03/52] libbpf: add function to get the pair BTF ID + type ID for a given type Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 04/52] libbpf: patch module BTF ID into BPF insns Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 05/52] net, xdp: decouple XDP code from the core networking code Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 06/52] bpf: pass a pointer to union bpf_attr to bpf_link_ops::update_prog() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 07/52] net, xdp: remove redundant arguments from dev_xdp_{at,de}tach_link() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 08/52] net, xdp: factor out XDP install arguments to a separate structure Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 09/52] net, xdp: add ability to specify BTF ID for XDP metadata Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 10/52] net, xdp: add ability to specify frame size threshold " Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 11/52] libbpf: factor out __bpf_set_link_xdp_fd_replace() args into a struct Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 12/52] libbpf: add ability to set the BTF/type ID on setting XDP prog Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 13/52] libbpf: add ability to set the meta threshold " Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 14/52] libbpf: pass &bpf_link_create_opts directly to bpf_program__attach_fd() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 15/52] libbpf: add bpf_program__attach_xdp_opts() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 16/52] selftests/bpf: expand xdp_link to check that setting meta opts works Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 17/52] samples/bpf: pass a struct to sample_install_xdp() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 18/52] samples/bpf: add ability to specify metadata threshold Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 19/52] stddef: make __struct_group() UAPI C++-friendly Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 20/52] net, xdp: move XDP metadata helpers into new xdp_meta.h Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 21/52] net, xdp: allow metadata > 32 Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 22/52] net, skbuff: add ability to skip skb metadata comparison Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 23/52] net, skbuff: constify the @skb argument of skb_hwtstamps() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 24/52] bpf, xdp: declare generic XDP metadata structure Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 25/52] net, xdp: add basic generic metadata accessors Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 26/52] bpf, btf: add a pair of function to work with the BTF ID + type ID pair Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 27/52] net, xdp: add &sk_buff <-> &xdp_meta_generic converters Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 28/52] net, xdp: prefetch data a bit when building an skb from an &xdp_frame Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 29/52] net, xdp: try to fill skb fields when converting " Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 30/52] net, gro: decouple GRO from the NAPI layer Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 31/52] net, gro: expose some GRO API to use outside of NAPI Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 32/52] bpf, cpumap: switch to GRO from netif_receive_skb_list() Alexander Lobakin
2024-08-07 20:38   ` [xdp-hints] " Daniel Xu
2024-08-08  4:54     ` Lorenzo Bianconi
2024-08-08 11:57       ` Alexander Lobakin
2024-08-08 17:22         ` Lorenzo Bianconi
2024-08-08 20:52         ` Daniel Xu
2024-08-09 10:02           ` Jesper Dangaard Brouer
2024-08-09 12:20           ` Alexander Lobakin
2024-08-09 12:45             ` Toke Høiland-Jørgensen
2024-08-09 12:56               ` Alexander Lobakin
2024-08-09 13:42                 ` Toke Høiland-Jørgensen
2024-08-10  0:54                   ` Martin KaFai Lau
2024-08-10  8:02                   ` Lorenzo Bianconi
2024-08-13  1:33             ` Jakub Kicinski
2024-08-13  9:51               ` Jesper Dangaard Brouer
2024-08-10  8:00         ` Lorenzo Bianconi
2024-08-13 14:09         ` Alexander Lobakin
2024-08-13 14:54           ` Toke Høiland-Jørgensen
2024-08-13 15:57             ` Jesper Dangaard Brouer
2024-08-19 14:50               ` Alexander Lobakin
2024-08-21  0:29                 ` Daniel Xu
2024-08-21 13:16                   ` Alexander Lobakin
2024-08-21 16:36                     ` Daniel Xu
2024-08-13 16:14           ` Lorenzo Bianconi
2024-08-13 16:27           ` Lorenzo Bianconi
2024-08-13 16:31             ` Alexander Lobakin
2024-08-08 20:44       ` Daniel Xu
2024-08-09  9:32         ` Jesper Dangaard Brouer
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 33/52] bpf, cpumap: add option to set a timeout for deferred flush Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 34/52] samples/bpf: add 'timeout' option to xdp_redirect_cpu Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 35/52] net, skbuff: introduce napi_skb_cache_get_bulk() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 36/52] bpf, cpumap: switch to napi_skb_cache_get_bulk() Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 37/52] rcupdate: fix access helpers for incomplete struct pointers on GCC < 10 Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 38/52] net, xdp: remove unused xdp_attachment_info::flags Alexander Lobakin
2022-06-28 19:47 ` [xdp-hints] [PATCH RFC bpf-next 39/52] net, xdp: make &xdp_attachment_info a bit more useful in drivers Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 40/52] net, xdp: add an RCU version of xdp_attachment_setup() Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 41/52] net, xdp: replace net_device::xdp_prog pointer with &xdp_attachment_info Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 42/52] net, xdp: shortcut skb->dev in bpf_prog_run_generic_xdp() Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 43/52] net, xdp: build XDP generic metadata on Generic (skb) XDP path Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 44/52] net, ice: allow XDP prog hot-swapping Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 45/52] net, ice: consolidate all skb fields processing Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 46/52] net, ice: use an onstack &xdp_meta_generic_rx to store HW frame info Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 47/52] net, ice: build XDP generic metadata Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 48/52] libbpf: compress Endianness ops with a macro Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 49/52] libbpf: add LE <--> CPU conversion helpers Alexander Lobakin
2022-06-28 19:48 ` Alexander Lobakin [this message]
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 51/52] selftests/bpf: fix using test_xdp_meta BPF prog via skeleton infra Alexander Lobakin
2022-06-28 19:48 ` [xdp-hints] [PATCH RFC bpf-next 52/52] selftests/bpf: add XDP Generic Hints selftest Alexander Lobakin
2022-06-29  6:15 ` [xdp-hints] Re: [PATCH RFC bpf-next 00/52] bpf, xdp: introduce and use Generic Hints/metadata John Fastabend
2022-06-29 13:43   ` Toke Høiland-Jørgensen
2022-07-04 15:44     ` Alexander Lobakin
2022-07-04 17:13       ` Jesper Dangaard Brouer
2022-07-05 14:38         ` Alexander Lobakin
2022-07-05 19:08           ` Daniel Borkmann
2022-07-04 17:14       ` Toke Høiland-Jørgensen
2022-07-05 15:41         ` Alexander Lobakin
2022-07-05 18:51           ` Toke Høiland-Jørgensen
2022-07-06 13:50             ` Alexander Lobakin
2022-07-06 23:22               ` Toke Høiland-Jørgensen
2022-07-07 11:41                 ` Jesper Dangaard Brouer
2022-07-12 10:33                 ` Magnus Karlsson
2022-07-12 14:14                   ` Jesper Dangaard Brouer
2022-07-15 11:11                     ` Magnus Karlsson
2022-06-29 17:56   ` Zvi Effron
2022-06-30  7:39     ` Magnus Karlsson
2022-07-04 15:31   ` Alexander Lobakin

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