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Message-Id: <0547d6f752e325f56a8e5f6466b50e81ff29d65f.1607349924.git.lorenzo@kernel.org>
Date: Mon, 7 Dec 2020 17:32:42 +0100
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: bpf@...r.kernel.org, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
daniel@...earbox.net, shayagr@...zon.com, sameehj@...zon.com,
john.fastabend@...il.com, dsahern@...nel.org, brouer@...hat.com,
echaudro@...hat.com, lorenzo.bianconi@...hat.com,
jasowang@...hat.com
Subject: [PATCH v5 bpf-next 13/14] bpf: add new frame_length field to the XDP ctx
From: Eelco Chaudron <echaudro@...hat.com>
This patch adds a new field to the XDP context called frame_length,
which will hold the full length of the packet, including fragments
if existing.
eBPF programs can determine if fragments are present using something
like:
if (ctx->data_end - ctx->data < ctx->frame_length) {
/* Fragements exists. /*
}
Signed-off-by: Eelco Chaudron <echaudro@...hat.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
---
include/net/xdp.h | 22 +++++++++
include/uapi/linux/bpf.h | 1 +
kernel/bpf/verifier.c | 2 +-
net/core/filter.c | 83 ++++++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 1 +
5 files changed, 108 insertions(+), 1 deletion(-)
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 09078ab6644c..e54d733c90ed 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -73,8 +73,30 @@ struct xdp_buff {
void *data_hard_start;
struct xdp_rxq_info *rxq;
struct xdp_txq_info *txq;
+ /* If any of the bitfield lengths for frame_sz or mb below change,
+ * make sure the defines here are also updated!
+ */
+#ifdef __BIG_ENDIAN_BITFIELD
+#define MB_SHIFT 0
+#define MB_MASK 0x00000001
+#define FRAME_SZ_SHIFT 1
+#define FRAME_SZ_MASK 0xfffffffe
+#else
+#define MB_SHIFT 31
+#define MB_MASK 0x80000000
+#define FRAME_SZ_SHIFT 0
+#define FRAME_SZ_MASK 0x7fffffff
+#endif
+#define FRAME_SZ_OFFSET() offsetof(struct xdp_buff, __u32_bit_fields_offset)
+#define MB_OFFSET() offsetof(struct xdp_buff, __u32_bit_fields_offset)
+ /* private: */
+ u32 __u32_bit_fields_offset[0];
+ /* public: */
u32 frame_sz:31; /* frame size to deduce data_hard_end/reserved tailroom*/
u32 mb:1; /* xdp non-linear buffer */
+
+ /* Temporary registers to make conditional access/stores possible. */
+ u64 tmp_reg[2];
};
/* Reserve memory area at end-of data area.
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 30b477a26482..62c50ab28ea9 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4380,6 +4380,7 @@ struct xdp_md {
__u32 rx_queue_index; /* rxq->queue_index */
__u32 egress_ifindex; /* txq->dev->ifindex */
+ __u32 frame_length;
};
/* DEVMAP map-value layout
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 93def76cf32b..c50caea29fa2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10526,7 +10526,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
const struct bpf_verifier_ops *ops = env->ops;
int i, cnt, size, ctx_field_size, delta = 0;
const int insn_cnt = env->prog->len;
- struct bpf_insn insn_buf[16], *insn;
+ struct bpf_insn insn_buf[32], *insn;
u32 target_size, size_default, off;
struct bpf_prog *new_prog;
enum bpf_access_type type;
diff --git a/net/core/filter.c b/net/core/filter.c
index 4c4882d4d92c..278640db9e0a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8908,6 +8908,7 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
struct bpf_insn *insn_buf,
struct bpf_prog *prog, u32 *target_size)
{
+ int ctx_reg, dst_reg, scratch_reg;
struct bpf_insn *insn = insn_buf;
switch (si->off) {
@@ -8954,6 +8955,88 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
offsetof(struct net_device, ifindex));
break;
+ case offsetof(struct xdp_md, frame_length):
+ /* Need tmp storage for src_reg in case src_reg == dst_reg,
+ * and a scratch reg */
+ scratch_reg = BPF_REG_9;
+ dst_reg = si->dst_reg;
+
+ if (dst_reg == scratch_reg)
+ scratch_reg--;
+
+ ctx_reg = (si->src_reg == si->dst_reg) ? scratch_reg - 1 : si->src_reg;
+ while (dst_reg == ctx_reg || scratch_reg == ctx_reg)
+ ctx_reg--;
+
+ /* Save scratch registers */
+ if (ctx_reg != si->src_reg) {
+ *insn++ = BPF_STX_MEM(BPF_DW, si->src_reg, ctx_reg,
+ offsetof(struct xdp_buff,
+ tmp_reg[1]));
+
+ *insn++ = BPF_MOV64_REG(ctx_reg, si->src_reg);
+ }
+
+ *insn++ = BPF_STX_MEM(BPF_DW, ctx_reg, scratch_reg,
+ offsetof(struct xdp_buff, tmp_reg[0]));
+
+ /* What does this code do?
+ * dst_reg = 0
+ *
+ * if (!ctx_reg->mb)
+ * goto no_mb:
+ *
+ * dst_reg = (struct xdp_shared_info *)xdp_data_hard_end(xdp)
+ * dst_reg = dst_reg->data_length
+ *
+ * NOTE: xdp_data_hard_end() is xdp->hard_start +
+ * xdp->frame_sz - sizeof(shared_info)
+ *
+ * no_mb:
+ * dst_reg += ctx_reg->data_end - ctx_reg->data
+ */
+ *insn++ = BPF_MOV64_IMM(dst_reg, 0);
+
+ *insn++ = BPF_LDX_MEM(BPF_W, scratch_reg, ctx_reg, MB_OFFSET());
+ *insn++ = BPF_ALU32_IMM(BPF_AND, scratch_reg, MB_MASK);
+ *insn++ = BPF_JMP_IMM(BPF_JEQ, scratch_reg, 0, 7); /*goto no_mb; */
+
+ *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct xdp_buff,
+ data_hard_start),
+ dst_reg, ctx_reg,
+ offsetof(struct xdp_buff, data_hard_start));
+ *insn++ = BPF_LDX_MEM(BPF_W, scratch_reg, ctx_reg,
+ FRAME_SZ_OFFSET());
+ *insn++ = BPF_ALU32_IMM(BPF_AND, scratch_reg, FRAME_SZ_MASK);
+ *insn++ = BPF_ALU32_IMM(BPF_RSH, scratch_reg, FRAME_SZ_SHIFT);
+ *insn++ = BPF_ALU64_REG(BPF_ADD, dst_reg, scratch_reg);
+ *insn++ = BPF_ALU64_IMM(BPF_SUB, dst_reg,
+ SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
+ *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct xdp_shared_info,
+ data_length),
+ dst_reg, dst_reg,
+ offsetof(struct xdp_shared_info,
+ data_length));
+
+ /* no_mb: */
+ *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct xdp_buff, data_end),
+ scratch_reg, ctx_reg,
+ offsetof(struct xdp_buff, data_end));
+ *insn++ = BPF_ALU64_REG(BPF_ADD, dst_reg, scratch_reg);
+ *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct xdp_buff, data),
+ scratch_reg, ctx_reg,
+ offsetof(struct xdp_buff, data));
+ *insn++ = BPF_ALU64_REG(BPF_SUB, dst_reg, scratch_reg);
+
+ /* Restore scratch registers */
+ *insn++ = BPF_LDX_MEM(BPF_DW, scratch_reg, ctx_reg,
+ offsetof(struct xdp_buff, tmp_reg[0]));
+
+ if (ctx_reg != si->src_reg)
+ *insn++ = BPF_LDX_MEM(BPF_DW, ctx_reg, ctx_reg,
+ offsetof(struct xdp_buff,
+ tmp_reg[1]));
+ break;
}
return insn - insn_buf;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 30b477a26482..62c50ab28ea9 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4380,6 +4380,7 @@ struct xdp_md {
__u32 rx_queue_index; /* rxq->queue_index */
__u32 egress_ifindex; /* txq->dev->ifindex */
+ __u32 frame_length;
};
/* DEVMAP map-value layout
--
2.28.0
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