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bpf: decouple stack_map_get_build_id_offset() from perf_callchain_entry

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Change stack_map_get_build_id_offset() which is used to convert stack
trace IP addresses into build ID+offset pairs. Right now this function
accepts an array of u64s as an input, and uses array of
struct bpf_stack_build_id as an output.

This is problematic because u64 array is coming from
perf_callchain_entry, which is (non-sleepable) RCU protected, so once we
allows sleepable build ID fetching, this all breaks down.

But its actually pretty easy to make stack_map_get_build_id_offset()
works with array of struct bpf_stack_build_id as both input and output.
Which is what this patch is doing, eliminating the dependency on
perf_callchain_entry. We require caller to fill out
bpf_stack_build_id.ip fields (all other can be left uninitialized), and
update in place as we do build ID resolution.

We make sure to READ_ONCE() and cache locally current IP value as we
used it in a few places to find matching VMA and so on. Given this data
is directly accessible and modifiable by user's BPF code, we should make
sure to have a consistent view of it.

Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240829174232.3133883-9-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2024-08-29 10:42:30 -07:00 committed by Alexei Starovoitov
parent cdbb44f9a7
commit 4f4c4fc015
1 changed files with 33 additions and 16 deletions
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49
kernel/bpf/stackmap.c
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@ -124,8 +124,18 @@ free_smap:
return ERR_PTR(err);
}
/*
* Expects all id_offs[i].ip values to be set to correct initial IPs.
* They will be subsequently:
* - either adjusted in place to a file offset, if build ID fetching
* succeeds; in this case id_offs[i].build_id is set to correct build ID,
* and id_offs[i].status is set to BPF_STACK_BUILD_ID_VALID;
* - or IP will be kept intact, if build ID fetching failed; in this case
* id_offs[i].build_id is zeroed out and id_offs[i].status is set to
* BPF_STACK_BUILD_ID_IP.
*/
static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
u64 *ips, u32 trace_nr, bool user)
u32 trace_nr, bool user)
{
int i;
struct mmap_unlock_irq_work *work = NULL;
@ -142,30 +152,28 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
/* cannot access current->mm, fall back to ips */
for (i = 0; i < trace_nr; i++) {
id_offs[i].status = BPF_STACK_BUILD_ID_IP;
id_offs[i].ip = ips[i];
memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
}
return;
}
for (i = 0; i < trace_nr; i++) {
if (range_in_vma(prev_vma, ips[i], ips[i])) {
u64 ip = READ_ONCE(id_offs[i].ip);
if (range_in_vma(prev_vma, ip, ip)) {
vma = prev_vma;
memcpy(id_offs[i].build_id, prev_build_id,
BUILD_ID_SIZE_MAX);
memcpy(id_offs[i].build_id, prev_build_id, BUILD_ID_SIZE_MAX);
goto build_id_valid;
}
vma = find_vma(current->mm, ips[i]);
vma = find_vma(current->mm, ip);
if (!vma || build_id_parse_nofault(vma, id_offs[i].build_id, NULL)) {
/* per entry fall back to ips */
id_offs[i].status = BPF_STACK_BUILD_ID_IP;
id_offs[i].ip = ips[i];
memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
continue;
}
build_id_valid:
id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ips[i]
- vma->vm_start;
id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ip - vma->vm_start;
id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
prev_vma = vma;
prev_build_id = id_offs[i].build_id;
@ -216,7 +224,7 @@ static long __bpf_get_stackid(struct bpf_map *map,
struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
u32 hash, id, trace_nr, trace_len;
u32 hash, id, trace_nr, trace_len, i;
bool user = flags & BPF_F_USER_STACK;
u64 *ips;
bool hash_matches;
@ -238,15 +246,18 @@ static long __bpf_get_stackid(struct bpf_map *map,
return id;
if (stack_map_use_build_id(map)) {
struct bpf_stack_build_id *id_offs;
/* for build_id+offset, pop a bucket before slow cmp */
new_bucket = (struct stack_map_bucket *)
pcpu_freelist_pop(&smap->freelist);
if (unlikely(!new_bucket))
return -ENOMEM;
new_bucket->nr = trace_nr;
stack_map_get_build_id_offset(
(struct bpf_stack_build_id *)new_bucket->data,
ips, trace_nr, user);
id_offs = (struct bpf_stack_build_id *)new_bucket->data;
for (i = 0; i < trace_nr; i++)
id_offs[i].ip = ips[i];
stack_map_get_build_id_offset(id_offs, trace_nr, user);
trace_len = trace_nr * sizeof(struct bpf_stack_build_id);
if (hash_matches && bucket->nr == trace_nr &&
memcmp(bucket->data, new_bucket->data, trace_len) == 0) {
@ -445,10 +456,16 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
copy_len = trace_nr * elem_size;
ips = trace->ip + skip;
if (user && user_build_id)
stack_map_get_build_id_offset(buf, ips, trace_nr, user);
else
if (user && user_build_id) {
struct bpf_stack_build_id *id_offs = buf;
u32 i;
for (i = 0; i < trace_nr; i++)
id_offs[i].ip = ips[i];
stack_map_get_build_id_offset(buf, trace_nr, user);
} else {
memcpy(buf, ips, copy_len);
}
if (size > copy_len)
memset(buf + copy_len, 0, size - copy_len);