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libbpf: Auto-bump RLIMIT_MEMLOCK if kernel needs it for BPF

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The need to increase RLIMIT_MEMLOCK to do anything useful with BPF is
one of the first extremely frustrating gotchas that all new BPF users go
through and in some cases have to learn it a very hard way.

Luckily, starting with upstream Linux kernel version 5.11, BPF subsystem
dropped the dependency on memlock and uses memcg-based memory accounting
instead. Unfortunately, detecting memcg-based BPF memory accounting is
far from trivial (as can be evidenced by this patch), so in practice
most BPF applications still do unconditional RLIMIT_MEMLOCK increase.

As we move towards libbpf 1.0, it would be good to allow users to forget
about RLIMIT_MEMLOCK vs memcg and let libbpf do the sensible adjustment
automatically. This patch paves the way forward in this matter. Libbpf
will do feature detection of memcg-based accounting, and if detected,
will do nothing. But if the kernel is too old, just like BCC, libbpf
will automatically increase RLIMIT_MEMLOCK on behalf of user
application ([0]).

As this is technically a breaking change, during the transition period
applications have to opt into libbpf 1.0 mode by setting
LIBBPF_STRICT_AUTO_RLIMIT_MEMLOCK bit when calling
libbpf_set_strict_mode().

Libbpf allows to control the exact amount of set RLIMIT_MEMLOCK limit
with libbpf_set_memlock_rlim_max() API. Passing 0 will make libbpf do
nothing with RLIMIT_MEMLOCK. libbpf_set_memlock_rlim_max() has to be
called before the first bpf_prog_load(), bpf_btf_load(), or
bpf_object__load() call, otherwise it has no effect and will return
-EBUSY.

  [0] Closes: https://github.com/libbpf/libbpf/issues/369

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211214195904.1785155-2-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-12-14 11:59:03 -08:00 committed by Daniel Borkmann
parent 9fc205b413
commit e542f2c4cd
6 changed files with 143 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

81
tools/lib/bpf/bpf.c
View File

@ -28,7 +28,9 @@
#include <asm/unistd.h>
#include <errno.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <limits.h>
#include <sys/resource.h>
#include "bpf.h"
#include "libbpf.h"
#include "libbpf_internal.h"
@ -94,6 +96,77 @@ static inline int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int
return fd;
}
/* Probe whether kernel switched from memlock-based (RLIMIT_MEMLOCK) to
* memcg-based memory accounting for BPF maps and progs. This was done in [0].
* We use the support for bpf_ktime_get_coarse_ns() helper, which was added in
* the same 5.11 Linux release ([1]), to detect memcg-based accounting for BPF.
*
* [0] https://lore.kernel.org/bpf/20201201215900.3569844-1-guro@fb.com/
* [1] d05512618056 ("bpf: Add bpf_ktime_get_coarse_ns helper")
*/
int probe_memcg_account(void)
{
const size_t prog_load_attr_sz = offsetofend(union bpf_attr, attach_btf_obj_fd);
struct bpf_insn insns[] = {
BPF_EMIT_CALL(BPF_FUNC_ktime_get_coarse_ns),
BPF_EXIT_INSN(),
};
size_t insn_cnt = sizeof(insns) / sizeof(insns[0]);
union bpf_attr attr;
int prog_fd;
/* attempt loading freplace trying to use custom BTF */
memset(&attr, 0, prog_load_attr_sz);
attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
attr.insns = ptr_to_u64(insns);
attr.insn_cnt = insn_cnt;
attr.license = ptr_to_u64("GPL");
prog_fd = sys_bpf_fd(BPF_PROG_LOAD, &attr, prog_load_attr_sz);
if (prog_fd >= 0) {
close(prog_fd);
return 1;
}
return 0;
}
static bool memlock_bumped;
static rlim_t memlock_rlim = RLIM_INFINITY;
int libbpf_set_memlock_rlim(size_t memlock_bytes)
{
if (memlock_bumped)
return libbpf_err(-EBUSY);
memlock_rlim = memlock_bytes;
return 0;
}
int bump_rlimit_memlock(void)
{
struct rlimit rlim;
/* this the default in libbpf 1.0, but for now user has to opt-in explicitly */
if (!(libbpf_mode & LIBBPF_STRICT_AUTO_RLIMIT_MEMLOCK))
return 0;
/* if kernel supports memcg-based accounting, skip bumping RLIMIT_MEMLOCK */
if (memlock_bumped || kernel_supports(NULL, FEAT_MEMCG_ACCOUNT))
return 0;
memlock_bumped = true;
/* zero memlock_rlim_max disables auto-bumping RLIMIT_MEMLOCK */
if (memlock_rlim == 0)
return 0;
rlim.rlim_cur = rlim.rlim_max = memlock_rlim;
if (setrlimit(RLIMIT_MEMLOCK, &rlim))
return -errno;
return 0;
}
int bpf_map_create(enum bpf_map_type map_type,
const char *map_name,
__u32 key_size,
@ -105,6 +178,8 @@ int bpf_map_create(enum bpf_map_type map_type,
union bpf_attr attr;
int fd;
bump_rlimit_memlock();
memset(&attr, 0, attr_sz);
if (!OPTS_VALID(opts, bpf_map_create_opts))
@ -251,6 +326,8 @@ int bpf_prog_load_v0_6_0(enum bpf_prog_type prog_type,
union bpf_attr attr;
char *log_buf;
bump_rlimit_memlock();
if (!OPTS_VALID(opts, bpf_prog_load_opts))
return libbpf_err(-EINVAL);
@ -456,6 +533,8 @@ int bpf_verify_program(enum bpf_prog_type type, const struct bpf_insn *insns,
union bpf_attr attr;
int fd;
bump_rlimit_memlock();
memset(&attr, 0, sizeof(attr));
attr.prog_type = type;
attr.insn_cnt = (__u32)insns_cnt;
@ -1056,6 +1135,8 @@ int bpf_btf_load(const void *btf_data, size_t btf_size, const struct bpf_btf_loa
__u32 log_level;
int fd;
bump_rlimit_memlock();
memset(&attr, 0, attr_sz);
if (!OPTS_VALID(opts, bpf_btf_load_opts))

2
tools/lib/bpf/bpf.h
View File

@ -35,6 +35,8 @@
extern "C" {
#endif
int libbpf_set_memlock_rlim(size_t memlock_bytes);
struct bpf_map_create_opts {
size_t sz; /* size of this struct for forward/backward compatibility */

47
tools/lib/bpf/libbpf.c
View File

@ -187,42 +187,6 @@ const char *libbpf_version_string(void)
#undef __S
}
enum kern_feature_id {
/* v4.14: kernel support for program & map names. */
FEAT_PROG_NAME,
/* v5.2: kernel support for global data sections. */
FEAT_GLOBAL_DATA,
/* BTF support */
FEAT_BTF,
/* BTF_KIND_FUNC and BTF_KIND_FUNC_PROTO support */
FEAT_BTF_FUNC,
/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
FEAT_BTF_DATASEC,
/* BTF_FUNC_GLOBAL is supported */
FEAT_BTF_GLOBAL_FUNC,
/* BPF_F_MMAPABLE is supported for arrays */
FEAT_ARRAY_MMAP,
/* kernel support for expected_attach_type in BPF_PROG_LOAD */
FEAT_EXP_ATTACH_TYPE,
/* bpf_probe_read_{kernel,user}[_str] helpers */
FEAT_PROBE_READ_KERN,
/* BPF_PROG_BIND_MAP is supported */
FEAT_PROG_BIND_MAP,
/* Kernel support for module BTFs */
FEAT_MODULE_BTF,
/* BTF_KIND_FLOAT support */
FEAT_BTF_FLOAT,
/* BPF perf link support */
FEAT_PERF_LINK,
/* BTF_KIND_DECL_TAG support */
FEAT_BTF_DECL_TAG,
/* BTF_KIND_TYPE_TAG support */
FEAT_BTF_TYPE_TAG,
__FEAT_CNT,
};
static bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id);
enum reloc_type {
RELO_LD64,
RELO_CALL,
@ -4352,6 +4316,10 @@ bpf_object__probe_loading(struct bpf_object *obj)
if (obj->gen_loader)
return 0;
ret = bump_rlimit_memlock();
if (ret)
pr_warn("Failed to bump RLIMIT_MEMLOCK (err = %d), you might need to do it explicitly!\n", ret);
/* make sure basic loading works */
ret = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL", insns, insn_cnt, NULL);
if (ret < 0)
@ -4718,14 +4686,17 @@ static struct kern_feature_desc {
[FEAT_BTF_TYPE_TAG] = {
"BTF_KIND_TYPE_TAG support", probe_kern_btf_type_tag,
},
[FEAT_MEMCG_ACCOUNT] = {
"memcg-based memory accounting", probe_memcg_account,
},
};
static bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
{
struct kern_feature_desc *feat = &feature_probes[feat_id];
int ret;
if (obj->gen_loader)
if (obj && obj->gen_loader)
/* To generate loader program assume the latest kernel
* to avoid doing extra prog_load, map_create syscalls.
*/

1
tools/lib/bpf/libbpf.map
View File

@ -427,4 +427,5 @@ LIBBPF_0.7.0 {
bpf_program__log_level;
bpf_program__set_log_buf;
bpf_program__set_log_level;
libbpf_set_memlock_rlim_max;
};

39
tools/lib/bpf/libbpf_internal.h
View File

@ -291,6 +291,45 @@ static inline bool libbpf_validate_opts(const char *opts,
(opts)->sz - __off); \
})
enum kern_feature_id {
/* v4.14: kernel support for program & map names. */
FEAT_PROG_NAME,
/* v5.2: kernel support for global data sections. */
FEAT_GLOBAL_DATA,
/* BTF support */
FEAT_BTF,
/* BTF_KIND_FUNC and BTF_KIND_FUNC_PROTO support */
FEAT_BTF_FUNC,
/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
FEAT_BTF_DATASEC,
/* BTF_FUNC_GLOBAL is supported */
FEAT_BTF_GLOBAL_FUNC,
/* BPF_F_MMAPABLE is supported for arrays */
FEAT_ARRAY_MMAP,
/* kernel support for expected_attach_type in BPF_PROG_LOAD */
FEAT_EXP_ATTACH_TYPE,
/* bpf_probe_read_{kernel,user}[_str] helpers */
FEAT_PROBE_READ_KERN,
/* BPF_PROG_BIND_MAP is supported */
FEAT_PROG_BIND_MAP,
/* Kernel support for module BTFs */
FEAT_MODULE_BTF,
/* BTF_KIND_FLOAT support */
FEAT_BTF_FLOAT,
/* BPF perf link support */
FEAT_PERF_LINK,
/* BTF_KIND_DECL_TAG support */
FEAT_BTF_DECL_TAG,
/* BTF_KIND_TYPE_TAG support */
FEAT_BTF_TYPE_TAG,
/* memcg-based accounting for BPF maps and progs */
FEAT_MEMCG_ACCOUNT,
__FEAT_CNT,
};
int probe_memcg_account(void);
bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id);
int bump_rlimit_memlock(void);
int parse_cpu_mask_str(const char *s, bool **mask, int *mask_sz);
int parse_cpu_mask_file(const char *fcpu, bool **mask, int *mask_sz);

12
tools/lib/bpf/libbpf_legacy.h
View File

@ -45,7 +45,6 @@ enum libbpf_strict_mode {
* (positive) error code.
*/
LIBBPF_STRICT_DIRECT_ERRS = 0x02,
/*
* Enforce strict BPF program section (SEC()) names.
* E.g., while prefiously SEC("xdp_whatever") or SEC("perf_event_blah") were
@ -63,6 +62,17 @@ enum libbpf_strict_mode {
* Clients can maintain it on their own if it is valuable for them.
*/
LIBBPF_STRICT_NO_OBJECT_LIST = 0x08,
/*
* Automatically bump RLIMIT_MEMLOCK using setrlimit() before the
* first BPF program or map creation operation. This is done only if
* kernel is too old to support memcg-based memory accounting for BPF
* subsystem. By default, RLIMIT_MEMLOCK limit is set to RLIM_INFINITY,
* but it can be overriden with libbpf_set_memlock_rlim_max() API.
* Note that libbpf_set_memlock_rlim_max() needs to be called before
* the very first bpf_prog_load(), bpf_map_create() or bpf_object__load()
* operation.
*/
LIBBPF_STRICT_AUTO_RLIMIT_MEMLOCK = 0x10,
__LIBBPF_STRICT_LAST,
};