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![Daniel Borkmann](/assets/img/avatar_default.png)
This work adds BPF_CALL_<n>() macros and converts all the eBPF helper functions to use them, in a similar fashion like we do with SYSCALL_DEFINE<n>() macros that are used today. Motivation for this is to hide all the register handling and all necessary casts from the user, so that it is done automatically in the background when adding a BPF_CALL_<n>() call. This makes current helpers easier to review, eases to write future helpers, avoids getting the casting mess wrong, and allows for extending all helpers at once (f.e. build time checks, etc). It also helps detecting more easily in code reviews that unused registers are not instrumented in the code by accident, breaking compatibility with existing programs. BPF_CALL_<n>() internals are quite similar to SYSCALL_DEFINE<n>() ones with some fundamental differences, for example, for generating the actual helper function that carries all u64 regs, we need to fill unused regs, so that we always end up with 5 u64 regs as an argument. I reviewed several 0-5 generated BPF_CALL_<n>() variants of the .i results and they look all as expected. No sparse issue spotted. We let this also sit for a few days with Fengguang's kbuild test robot, and there were no issues seen. On s390, it barked on the "uses dynamic stack allocation" notice, which is an old one from bpf_perf_event_output{,_tp}() reappearing here due to the conversion to the call wrapper, just telling that the perf raw record/frag sits on stack (gcc with s390's -mwarn-dynamicstack), but that's all. Did various runtime tests and they were fine as well. All eBPF helpers are now converted to use these macros, getting rid of a good chunk of all the raw castings. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
290 lines
7.3 KiB
C
290 lines
7.3 KiB
C
/* Copyright (c) 2016 Facebook
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*/
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#include <linux/bpf.h>
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#include <linux/jhash.h>
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#include <linux/filter.h>
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#include <linux/vmalloc.h>
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#include <linux/stacktrace.h>
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#include <linux/perf_event.h>
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#include "percpu_freelist.h"
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struct stack_map_bucket {
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struct pcpu_freelist_node fnode;
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u32 hash;
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u32 nr;
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u64 ip[];
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};
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struct bpf_stack_map {
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struct bpf_map map;
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void *elems;
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struct pcpu_freelist freelist;
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u32 n_buckets;
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struct stack_map_bucket *buckets[];
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};
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static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
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{
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u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
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int err;
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smap->elems = vzalloc(elem_size * smap->map.max_entries);
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if (!smap->elems)
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return -ENOMEM;
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err = pcpu_freelist_init(&smap->freelist);
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if (err)
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goto free_elems;
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pcpu_freelist_populate(&smap->freelist, smap->elems, elem_size,
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smap->map.max_entries);
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return 0;
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free_elems:
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vfree(smap->elems);
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return err;
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}
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/* Called from syscall */
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static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
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{
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u32 value_size = attr->value_size;
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struct bpf_stack_map *smap;
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u64 cost, n_buckets;
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int err;
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if (!capable(CAP_SYS_ADMIN))
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return ERR_PTR(-EPERM);
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if (attr->map_flags)
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return ERR_PTR(-EINVAL);
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/* check sanity of attributes */
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if (attr->max_entries == 0 || attr->key_size != 4 ||
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value_size < 8 || value_size % 8 ||
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value_size / 8 > sysctl_perf_event_max_stack)
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return ERR_PTR(-EINVAL);
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/* hash table size must be power of 2 */
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n_buckets = roundup_pow_of_two(attr->max_entries);
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cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
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if (cost >= U32_MAX - PAGE_SIZE)
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return ERR_PTR(-E2BIG);
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smap = kzalloc(cost, GFP_USER | __GFP_NOWARN);
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if (!smap) {
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smap = vzalloc(cost);
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if (!smap)
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return ERR_PTR(-ENOMEM);
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}
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err = -E2BIG;
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cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
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if (cost >= U32_MAX - PAGE_SIZE)
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goto free_smap;
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smap->map.map_type = attr->map_type;
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smap->map.key_size = attr->key_size;
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smap->map.value_size = value_size;
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smap->map.max_entries = attr->max_entries;
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smap->n_buckets = n_buckets;
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smap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
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err = bpf_map_precharge_memlock(smap->map.pages);
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if (err)
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goto free_smap;
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err = get_callchain_buffers(sysctl_perf_event_max_stack);
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if (err)
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goto free_smap;
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err = prealloc_elems_and_freelist(smap);
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if (err)
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goto put_buffers;
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return &smap->map;
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put_buffers:
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put_callchain_buffers();
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free_smap:
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kvfree(smap);
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return ERR_PTR(err);
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}
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BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
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u64, flags)
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{
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struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
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struct perf_callchain_entry *trace;
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struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
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u32 max_depth = map->value_size / 8;
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/* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */
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u32 init_nr = sysctl_perf_event_max_stack - max_depth;
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u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
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u32 hash, id, trace_nr, trace_len;
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bool user = flags & BPF_F_USER_STACK;
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bool kernel = !user;
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u64 *ips;
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if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
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BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
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return -EINVAL;
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trace = get_perf_callchain(regs, init_nr, kernel, user,
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sysctl_perf_event_max_stack, false, false);
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if (unlikely(!trace))
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/* couldn't fetch the stack trace */
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return -EFAULT;
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/* get_perf_callchain() guarantees that trace->nr >= init_nr
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* and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth
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*/
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trace_nr = trace->nr - init_nr;
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if (trace_nr <= skip)
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/* skipping more than usable stack trace */
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return -EFAULT;
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trace_nr -= skip;
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trace_len = trace_nr * sizeof(u64);
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ips = trace->ip + skip + init_nr;
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hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
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id = hash & (smap->n_buckets - 1);
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bucket = READ_ONCE(smap->buckets[id]);
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if (bucket && bucket->hash == hash) {
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if (flags & BPF_F_FAST_STACK_CMP)
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return id;
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if (bucket->nr == trace_nr &&
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memcmp(bucket->ip, ips, trace_len) == 0)
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return id;
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}
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/* this call stack is not in the map, try to add it */
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if (bucket && !(flags & BPF_F_REUSE_STACKID))
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return -EEXIST;
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new_bucket = (struct stack_map_bucket *)
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pcpu_freelist_pop(&smap->freelist);
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if (unlikely(!new_bucket))
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return -ENOMEM;
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memcpy(new_bucket->ip, ips, trace_len);
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new_bucket->hash = hash;
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new_bucket->nr = trace_nr;
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old_bucket = xchg(&smap->buckets[id], new_bucket);
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if (old_bucket)
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pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
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return id;
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}
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const struct bpf_func_proto bpf_get_stackid_proto = {
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.func = bpf_get_stackid,
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.gpl_only = true,
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.ret_type = RET_INTEGER,
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.arg1_type = ARG_PTR_TO_CTX,
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.arg2_type = ARG_CONST_MAP_PTR,
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.arg3_type = ARG_ANYTHING,
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};
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/* Called from eBPF program */
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static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
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{
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return NULL;
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}
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/* Called from syscall */
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int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
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{
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struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
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struct stack_map_bucket *bucket, *old_bucket;
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u32 id = *(u32 *)key, trace_len;
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if (unlikely(id >= smap->n_buckets))
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return -ENOENT;
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bucket = xchg(&smap->buckets[id], NULL);
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if (!bucket)
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return -ENOENT;
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trace_len = bucket->nr * sizeof(u64);
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memcpy(value, bucket->ip, trace_len);
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memset(value + trace_len, 0, map->value_size - trace_len);
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old_bucket = xchg(&smap->buckets[id], bucket);
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if (old_bucket)
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pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
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return 0;
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}
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static int stack_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
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{
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return -EINVAL;
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}
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static int stack_map_update_elem(struct bpf_map *map, void *key, void *value,
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u64 map_flags)
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{
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return -EINVAL;
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}
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/* Called from syscall or from eBPF program */
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static int stack_map_delete_elem(struct bpf_map *map, void *key)
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{
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struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
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struct stack_map_bucket *old_bucket;
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u32 id = *(u32 *)key;
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if (unlikely(id >= smap->n_buckets))
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return -E2BIG;
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old_bucket = xchg(&smap->buckets[id], NULL);
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if (old_bucket) {
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pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
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return 0;
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} else {
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return -ENOENT;
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}
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}
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/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
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static void stack_map_free(struct bpf_map *map)
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{
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struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
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/* wait for bpf programs to complete before freeing stack map */
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synchronize_rcu();
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vfree(smap->elems);
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pcpu_freelist_destroy(&smap->freelist);
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kvfree(smap);
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put_callchain_buffers();
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}
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static const struct bpf_map_ops stack_map_ops = {
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.map_alloc = stack_map_alloc,
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.map_free = stack_map_free,
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.map_get_next_key = stack_map_get_next_key,
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.map_lookup_elem = stack_map_lookup_elem,
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.map_update_elem = stack_map_update_elem,
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.map_delete_elem = stack_map_delete_elem,
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};
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static struct bpf_map_type_list stack_map_type __read_mostly = {
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.ops = &stack_map_ops,
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.type = BPF_MAP_TYPE_STACK_TRACE,
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};
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static int __init register_stack_map(void)
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{
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bpf_register_map_type(&stack_map_type);
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return 0;
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}
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late_initcall(register_stack_map);
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