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Message-Id: <20250520-vmlinux-mmap-v5-3-e8c941acc414@isovalent.com>
Date: Tue, 20 May 2025 14:01:19 +0100
From: Lorenz Bauer <lmb@...valent.com>
To: Arnd Bergmann <arnd@...db.de>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>,
Shuah Khan <shuah@...nel.org>
Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
Lorenz Bauer <lmb@...valent.com>, Alan Maguire <alan.maguire@...cle.com>
Subject: [PATCH bpf-next v5 3/3] libbpf: Use mmap to parse vmlinux BTF from
sysfs
Teach libbpf to use mmap when parsing vmlinux BTF from /sys. We don't
apply this to fall-back paths on the regular file system because there
is no way to ensure that modifications underlying the MAP_PRIVATE
mapping are not visible to the process.
Acked-by: Andrii Nakryiko <andrii@...nel.org>
Tested-by: Alan Maguire <alan.maguire@...cle.com>
Signed-off-by: Lorenz Bauer <lmb@...valent.com>
---
tools/lib/bpf/btf.c | 89 ++++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 71 insertions(+), 18 deletions(-)
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index f18d7e6a453cd9e5c384487659df04f7efafdf5a..3b98ac40bbd66c4fa688f967f9370b5c92610ba0 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -12,6 +12,7 @@
#include <sys/utsname.h>
#include <sys/param.h>
#include <sys/stat.h>
+#include <sys/mman.h>
#include <linux/kernel.h>
#include <linux/err.h>
#include <linux/btf.h>
@@ -120,6 +121,9 @@ struct btf {
/* whether base_btf should be freed in btf_free for this instance */
bool owns_base;
+ /* whether raw_data is a (read-only) mmap */
+ bool raw_data_is_mmap;
+
/* BTF object FD, if loaded into kernel */
int fd;
@@ -951,6 +955,17 @@ static bool btf_is_modifiable(const struct btf *btf)
return (void *)btf->hdr != btf->raw_data;
}
+static void btf_free_raw_data(struct btf *btf)
+{
+ if (btf->raw_data_is_mmap) {
+ munmap(btf->raw_data, btf->raw_size);
+ btf->raw_data_is_mmap = false;
+ } else {
+ free(btf->raw_data);
+ }
+ btf->raw_data = NULL;
+}
+
void btf__free(struct btf *btf)
{
if (IS_ERR_OR_NULL(btf))
@@ -970,7 +985,7 @@ void btf__free(struct btf *btf)
free(btf->types_data);
strset__free(btf->strs_set);
}
- free(btf->raw_data);
+ btf_free_raw_data(btf);
free(btf->raw_data_swapped);
free(btf->type_offs);
if (btf->owns_base)
@@ -1030,7 +1045,7 @@ struct btf *btf__new_empty_split(struct btf *base_btf)
return libbpf_ptr(btf_new_empty(base_btf));
}
-static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
+static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf, bool is_mmap)
{
struct btf *btf;
int err;
@@ -1050,12 +1065,18 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
btf->start_str_off = base_btf->hdr->str_len;
}
- btf->raw_data = malloc(size);
- if (!btf->raw_data) {
- err = -ENOMEM;
- goto done;
+ if (is_mmap) {
+ btf->raw_data = (void *)data;
+ btf->raw_data_is_mmap = true;
+ } else {
+ btf->raw_data = malloc(size);
+ if (!btf->raw_data) {
+ err = -ENOMEM;
+ goto done;
+ }
+ memcpy(btf->raw_data, data, size);
}
- memcpy(btf->raw_data, data, size);
+
btf->raw_size = size;
btf->hdr = btf->raw_data;
@@ -1083,12 +1104,12 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
struct btf *btf__new(const void *data, __u32 size)
{
- return libbpf_ptr(btf_new(data, size, NULL));
+ return libbpf_ptr(btf_new(data, size, NULL, false));
}
struct btf *btf__new_split(const void *data, __u32 size, struct btf *base_btf)
{
- return libbpf_ptr(btf_new(data, size, base_btf));
+ return libbpf_ptr(btf_new(data, size, base_btf, false));
}
struct btf_elf_secs {
@@ -1209,7 +1230,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
if (secs.btf_base_data) {
dist_base_btf = btf_new(secs.btf_base_data->d_buf, secs.btf_base_data->d_size,
- NULL);
+ NULL, false);
if (IS_ERR(dist_base_btf)) {
err = PTR_ERR(dist_base_btf);
dist_base_btf = NULL;
@@ -1218,7 +1239,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
}
btf = btf_new(secs.btf_data->d_buf, secs.btf_data->d_size,
- dist_base_btf ?: base_btf);
+ dist_base_btf ?: base_btf, false);
if (IS_ERR(btf)) {
err = PTR_ERR(btf);
goto done;
@@ -1335,7 +1356,7 @@ static struct btf *btf_parse_raw(const char *path, struct btf *base_btf)
}
/* finally parse BTF data */
- btf = btf_new(data, sz, base_btf);
+ btf = btf_new(data, sz, base_btf, false);
err_out:
free(data);
@@ -1354,6 +1375,37 @@ struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf)
return libbpf_ptr(btf_parse_raw(path, base_btf));
}
+static struct btf *btf_parse_raw_mmap(const char *path, struct btf *base_btf)
+{
+ struct stat st;
+ void *data;
+ struct btf *btf;
+ int fd, err;
+
+ fd = open(path, O_RDONLY);
+ if (fd < 0)
+ return libbpf_err_ptr(-errno);
+
+ if (fstat(fd, &st) < 0) {
+ err = -errno;
+ close(fd);
+ return libbpf_err_ptr(err);
+ }
+
+ data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+ err = -errno;
+ close(fd);
+
+ if (data == MAP_FAILED)
+ return libbpf_err_ptr(err);
+
+ btf = btf_new(data, st.st_size, base_btf, true);
+ if (IS_ERR(btf))
+ munmap(data, st.st_size);
+
+ return btf;
+}
+
static struct btf *btf_parse(const char *path, struct btf *base_btf, struct btf_ext **btf_ext)
{
struct btf *btf;
@@ -1618,7 +1670,7 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
goto exit_free;
}
- btf = btf_new(ptr, btf_info.btf_size, base_btf);
+ btf = btf_new(ptr, btf_info.btf_size, base_btf, false);
exit_free:
free(ptr);
@@ -1658,10 +1710,8 @@ struct btf *btf__load_from_kernel_by_id(__u32 id)
static void btf_invalidate_raw_data(struct btf *btf)
{
- if (btf->raw_data) {
- free(btf->raw_data);
- btf->raw_data = NULL;
- }
+ if (btf->raw_data)
+ btf_free_raw_data(btf);
if (btf->raw_data_swapped) {
free(btf->raw_data_swapped);
btf->raw_data_swapped = NULL;
@@ -5331,7 +5381,10 @@ struct btf *btf__load_vmlinux_btf(void)
pr_warn("kernel BTF is missing at '%s', was CONFIG_DEBUG_INFO_BTF enabled?\n",
sysfs_btf_path);
} else {
- btf = btf__parse(sysfs_btf_path, NULL);
+ btf = btf_parse_raw_mmap(sysfs_btf_path, NULL);
+ if (IS_ERR(btf))
+ btf = btf__parse(sysfs_btf_path, NULL);
+
if (!btf) {
err = -errno;
pr_warn("failed to read kernel BTF from '%s': %s\n",
--
2.49.0
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