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In the commit7c4cd051ad("bpf: Fix syscall's stackmap lookup potential deadlock"), a potential deadlock issue was addressed, which resulted in *_map_lookup_elem not triggering BPF programs. (prior to lookup, bpf_disable_instrumentation() is used) To resolve the broken map lookup probe using "htab_map_lookup_elem", this commit introduces an alternative approach. Instead, it utilize "bpf_map_copy_value" and apply a filter specifically for the hash table with map_type. Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com> Fixes:7c4cd051ad("bpf: Fix syscall's stackmap lookup potential deadlock") Link: https://lore.kernel.org/r/20230818090119.477441-8-danieltimlee@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
82 lines
1.9 KiB
C
82 lines
1.9 KiB
C
#include "vmlinux.h"
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#include <linux/version.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_core_read.h>
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struct {
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__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
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__uint(key_size, sizeof(int));
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__uint(value_size, sizeof(u32));
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__uint(max_entries, 64);
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} counters SEC(".maps");
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__type(key, int);
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__type(value, u64);
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__uint(max_entries, 64);
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} values SEC(".maps");
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__type(key, int);
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__type(value, struct bpf_perf_event_value);
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__uint(max_entries, 64);
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} values2 SEC(".maps");
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SEC("kprobe/htab_map_get_next_key")
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int bpf_prog1(struct pt_regs *ctx)
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{
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u32 key = bpf_get_smp_processor_id();
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u64 count, *val;
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s64 error;
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count = bpf_perf_event_read(&counters, key);
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error = (s64)count;
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if (error <= -2 && error >= -22)
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return 0;
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val = bpf_map_lookup_elem(&values, &key);
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if (val)
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*val = count;
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else
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bpf_map_update_elem(&values, &key, &count, BPF_NOEXIST);
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return 0;
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}
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/*
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* Since *_map_lookup_elem can't be expected to trigger bpf programs
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* due to potential deadlocks (bpf_disable_instrumentation), this bpf
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* program will be attached to bpf_map_copy_value (which is called
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* from map_lookup_elem) and will only filter the hashtable type.
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*/
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SEC("kprobe/bpf_map_copy_value")
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int BPF_KPROBE(bpf_prog2, struct bpf_map *map)
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{
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u32 key = bpf_get_smp_processor_id();
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struct bpf_perf_event_value *val, buf;
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enum bpf_map_type type;
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int error;
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type = BPF_CORE_READ(map, map_type);
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if (type != BPF_MAP_TYPE_HASH)
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return 0;
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error = bpf_perf_event_read_value(&counters, key, &buf, sizeof(buf));
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if (error)
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return 0;
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val = bpf_map_lookup_elem(&values2, &key);
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if (val)
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*val = buf;
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else
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bpf_map_update_elem(&values2, &key, &buf, BPF_NOEXIST);
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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u32 _version SEC("version") = LINUX_VERSION_CODE;
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