From: Matt Corallo Date: Thu, 10 Jun 2021 03:43:02 +0000 (+0000) Subject: Rewrite per-source ratelimiting rules to use a custom hashtable X-Git-Url: http://git.bitcoin.ninja/index.cgi?p=flowspec-xdp;a=commitdiff_plain;h=14f8186f33558b42201be806e9725acd3d445182 Rewrite per-source ratelimiting rules to use a custom hashtable The in-kernel hashtable isn't at all fancy, and we can just use a custom one to get basically the same outcomes, with much less overhead due to the per-CPU stuff we have to do to get sensible multicore access rules. --- diff --git a/genrules.py b/genrules.py index a8ad71a..a09fde1 100755 --- a/genrules.py +++ b/genrules.py @@ -412,21 +412,24 @@ with open("rules.h", "w") as out: first_action += "struct ratelimit *rate = bpf_map_lookup_elem(&rate_map, &ratelimitidx);\n" ratelimitcnt += 1 else: - spin_lock = "/* No locking as we're per-CPU */" - spin_unlock = "/* No locking as we're per-CPU */" + spin_lock = "/* No locking as we're locked in get_v*_persrc_ratelimit */" + spin_unlock = "bpf_spin_unlock(rate_ptr.lock);" if proto == 4: if mid_byte > 32: continue first_action += f"const uint32_t srcip = ip->saddr & MASK4({mid_byte});\n" first_action += f"void *rate_map = &v4_src_rate_{len(v4persrcratelimits)};\n" + first_action += f"struct persrc_rate4_ptr rate_ptr = get_v4_persrc_ratelimit(srcip, rate_map, {(high_byte + 1) * 1024});\n" + first_action += f"struct persrc_rate4_entry *rate = rate_ptr.rate;\n" v4persrcratelimits.append((high_byte + 1) * 1024) else: if mid_byte > 128: continue first_action += f"const uint128_t srcip = ip6->saddr & MASK6({mid_byte});\n" first_action += f"void *rate_map = &v6_src_rate_{len(v6persrcratelimits)};\n" + first_action += f"struct persrc_rate6_ptr rate_ptr = get_v6_persrc_ratelimit(srcip, rate_map, {(high_byte + 1) * 1024});\n" + first_action += f"struct persrc_rate6_entry *rate = rate_ptr.rate;\n" v6persrcratelimits.append((high_byte + 1) * 1024) - first_action += f"struct percpu_ratelimit *rate = bpf_map_lookup_elem(rate_map, &srcip);\n" first_action += "if (rate) {\n" first_action += f"\t{spin_lock}\n" first_action += "\tif (likely(rate->sent_rate > 0))" + " {\n" @@ -449,15 +452,6 @@ with open("rules.h", "w") as out: first_action += "\t\t{stats_replace}\n" first_action += "\t\treturn XDP_DROP;\n" first_action += "\t}\n" - if ty == "0x8306" or ty == "0x830c": - first_action += "} else {\n" - first_action += "\tstruct percpu_ratelimit new_rate = { .sent_time = time, };\n" - first_action += "\trate = &new_rate;\n" - if ty == "0x8006" or ty == "0x8306": - first_action += f"\t\trate->sent_rate = data_end - pktdata;\n" - else: - first_action += f"\t\trate->sent_rate = 1;\n" - first_action += "\tbpf_map_update_elem(rate_map, &srcip, rate, BPF_ANY);\n" first_action += "}\n" elif ty == "0x8007": if low_bytes & 1 == 0: @@ -509,6 +503,6 @@ with open("rules.h", "w") as out: out.write("#define PARSE_V6_FRAG PARSE\n") with open("maps.h", "w") as out: for idx, limit in enumerate(v4persrcratelimits): - out.write(f"V4_SRC_RATE_DEFINE({idx}, {limit})\n") + out.write(f"SRC_RATE_DEFINE(4, {idx}, {limit})\n") for idx, limit in enumerate(v6persrcratelimits): - out.write(f"V6_SRC_RATE_DEFINE({idx}, {limit})\n") + out.write(f"SRC_RATE_DEFINE(6, {idx}, {limit})\n") diff --git a/install.sh b/install.sh index d77a8b0..b8f83ab 100755 --- a/install.sh +++ b/install.sh @@ -15,10 +15,12 @@ fi RULES="$(birdc show route table flowspec4 primary all) $(birdc show route table flowspec6 primary all)" +echo "const uint8_t COMPILE_TIME_RAND[] = { $(dd if=/dev/urandom of=/dev/stdout bs=1 count=8 2>/dev/null | hexdump -e '4/1 "0x%02x, "') };" > rand.h + echo "$RULES" | ./genrules.py --8021q=drop-vlan --v6frag=ignore-parse-if-rule --ihl=parse-options -clang $CLANG_ARGS -g -std=c99 -pedantic -Wall -Wextra -Wno-pointer-arith -Wno-unused-variable -O3 -emit-llvm -c xdp.c -o xdp.bc +clang $CLANG_ARGS -g -std=c99 -pedantic -Wall -Wextra -Wno-pointer-arith -Wno-unused-variable -Wno-unused-function -O3 -emit-llvm -c xdp.c -o xdp.bc if [ "$2" != "" ]; then - clang $4 -g -std=c99 -pedantic -Wall -Wextra -Wno-pointer-arith -Wno-unused-variable -O3 -emit-llvm -c "$2" -o wrapper.bc + clang $4 -g -std=c99 -pedantic -Wall -Wextra -Wno-pointer-arith -O3 -emit-llvm -c "$2" -o wrapper.bc llvm-link xdp.bc wrapper.bc | llc -O3 -march=bpf -filetype=obj -o xdp else cat xdp.bc | llc -O3 -march=bpf -filetype=obj -o xdp diff --git a/xdp.c b/xdp.c index 1344acd..6c9a01a 100644 --- a/xdp.c +++ b/xdp.c @@ -186,32 +186,89 @@ struct { } rate_map SEC(".maps"); #endif /* RATE_CNT */ -// For per-source rate limiting, we have to use per-CPU hash maps as Linux -// doesn't support spinlocks inside of a LRU_HASH (see if block in -// map_check_btf as of Linux 5.10). -// This isn't exactly accurate, but at least its faster. -struct percpu_ratelimit { - int64_t sent_rate; - int64_t sent_time; -}; +// We implement a rather naive hashtable here instead of using a BPF map because +// (a) the BPF map hashtables are similarly naive (no rehashing, etc), +// (b) the BPF map LRU hashtables don't support locking. +// +// We first separate into a few top-level buckets with per-bucket locks, limiting +// us to 2^SRC_HASH_MAX_PARALLELISM parallel accessors. +// +// Then we build an array of MAX_ENTRIES/2**SRC_HASH_MAX_PARALLELISM_POW entries, +// which are split into buckets of size SRC_HASH_BUCKET_COUNT. An entry can appear +// in any of the SRC_HASH_BUCKET_COUNT buckets at it's hash value. +#define SRC_HASH_MAX_PARALLELISM_POW 7 +#define SRC_HASH_MAX_PARALLELISM (1 << SRC_HASH_MAX_PARALLELISM_POW) +#define SRC_HASH_BUCKET_COUNT_POW 3 +#define SRC_HASH_BUCKET_COUNT (1 << SRC_HASH_BUCKET_COUNT_POW) + +#include "rand.h" + +#define CREATE_PERSRC_LOOKUP(IPV, IP_TYPE) \ +struct persrc_rate##IPV##_entry { \ + int64_t sent_rate; \ + int64_t sent_time; \ + IP_TYPE srcip; \ +}; \ + \ +struct persrc_rate##IPV##_bucket { \ + struct bpf_spin_lock lock; \ + struct persrc_rate##IPV##_entry entries[]; \ +}; \ + \ +struct persrc_rate##IPV##_ptr { \ + struct persrc_rate##IPV##_entry *rate; \ + struct bpf_spin_lock *lock; \ +}; \ + \ +__attribute__((always_inline)) \ +static inline struct persrc_rate##IPV##_ptr get_v##IPV##_persrc_ratelimit(IP_TYPE key, void *map, size_t map_limit) { \ + struct persrc_rate##IPV##_ptr res = { .rate = NULL, .lock = NULL }; \ + uint64_t hash = siphash(&key, sizeof(key), COMPILE_TIME_RAND); \ + \ + const uint32_t map_key = hash % SRC_HASH_MAX_PARALLELISM; \ + struct persrc_rate##IPV##_bucket *buckets = bpf_map_lookup_elem(map, &map_key); \ + if (!buckets) return res; \ + \ + hash >>= SRC_HASH_MAX_PARALLELISM_POW; \ + map_limit >>= SRC_HASH_MAX_PARALLELISM_POW; \ + \ + struct persrc_rate##IPV##_entry *first_bucket = &buckets->entries[(hash % map_limit) & (~(SRC_HASH_BUCKET_COUNT - 1))]; \ + bpf_spin_lock(&buckets->lock); \ + \ + int min_sent_idx = 0; \ + int64_t min_sent_time = INT64_MAX; \ + for (int i = 0; i < SRC_HASH_BUCKET_COUNT; i++) { \ + if (first_bucket[i].srcip == key) { \ + res.rate = &first_bucket[i]; \ + res.lock = &buckets->lock; \ + return res; \ + } else if (min_sent_time > first_bucket[i].sent_time) { \ + min_sent_time = first_bucket[i].sent_time; \ + min_sent_idx = i; \ + } \ + } \ + res.rate = &first_bucket[min_sent_idx]; \ + res.rate->srcip = key; \ + res.rate->sent_rate = 0; \ + res.rate->sent_time = 0; \ + res.lock = &buckets->lock; \ + return res; \ +} -#define V6_SRC_RATE_DEFINE(n, limit) \ -struct { \ - __uint(type, BPF_MAP_TYPE_LRU_PERCPU_HASH); \ - __uint(map_flags, BPF_F_NO_COMMON_LRU); \ - __uint(max_entries, limit); \ - uint128_t *key; \ - struct percpu_ratelimit *value; \ -} v6_src_rate_##n SEC(".maps"); - -#define V4_SRC_RATE_DEFINE(n, limit) \ +CREATE_PERSRC_LOOKUP(6, uint128_t) +CREATE_PERSRC_LOOKUP(4, uint32_t) + +#define SRC_RATE_DEFINE(IPV, n, limit) \ +struct persrc_rate##IPV##_bucket_##n { \ + struct bpf_spin_lock lock; \ + struct persrc_rate##IPV##_entry entries[limit / SRC_HASH_MAX_PARALLELISM]; \ +}; \ struct { \ - __uint(type, BPF_MAP_TYPE_LRU_PERCPU_HASH); \ - __uint(map_flags, BPF_F_NO_COMMON_LRU); \ - __uint(max_entries, limit); \ - __u32 *key; \ - struct percpu_ratelimit *value; \ -} v4_src_rate_##n SEC(".maps"); + __uint(type, BPF_MAP_TYPE_ARRAY); \ + __uint(max_entries, SRC_HASH_MAX_PARALLELISM); \ + uint32_t *key; \ + struct persrc_rate##IPV##_bucket_##n *value; \ +} v##IPV##_src_rate_##n SEC(".maps"); #include "maps.h"