From 06e71ad534881d2a09ced7509d2ab0daedac4c96 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Mon, 8 Jul 2024 13:45:38 -0700 Subject: [PATCH 1/3] bpftool: improve skeleton backwards compat with old buggy libbpfs Old versions of libbpf don't handle varying sizes of bpf_map_skeleton struct correctly. As such, BPF skeleton generated by newest bpftool might not be compatible with older libbpf (though only when libbpf is used as a shared library), even though it, by design, should. Going forward libbpf will be fixed, plus we'll release bug fixed versions of relevant old libbpfs, but meanwhile try to mitigate from bpftool side by conservatively assuming older and smaller definition of bpf_map_skeleton, if possible. Meaning, if there are no struct_ops maps. If there are struct_ops, then presumably user would like to have auto-attaching logic and struct_ops map link placeholders, so use the full bpf_map_skeleton definition in that case. Acked-by: Quentin Monnet Co-developed-by: Mykyta Yatsenko Signed-off-by: Mykyta Yatsenko Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman Link: https://lore.kernel.org/r/20240708204540.4188946-2-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- tools/bpf/bpftool/gen.c | 46 ++++++++++++++++++++++++++++------------- 1 file changed, 32 insertions(+), 14 deletions(-) diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c index 51eaed76db97..5a4d3240689e 100644 --- a/tools/bpf/bpftool/gen.c +++ b/tools/bpf/bpftool/gen.c @@ -852,24 +852,41 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped, bool { struct bpf_map *map; char ident[256]; - size_t i; + size_t i, map_sz; if (!map_cnt) return; + /* for backward compatibility with old libbpf versions that don't + * handle new BPF skeleton with new struct bpf_map_skeleton definition + * that includes link field, avoid specifying new increased size, + * unless we absolutely have to (i.e., if there are struct_ops maps + * present) + */ + map_sz = offsetof(struct bpf_map_skeleton, link); + if (populate_links) { + bpf_object__for_each_map(map, obj) { + if (bpf_map__type(map) == BPF_MAP_TYPE_STRUCT_OPS) { + map_sz = sizeof(struct bpf_map_skeleton); + break; + } + } + } + codegen("\ \n\ - \n\ + \n\ /* maps */ \n\ s->map_cnt = %zu; \n\ - s->map_skel_sz = sizeof(*s->maps); \n\ - s->maps = (struct bpf_map_skeleton *)calloc(s->map_cnt, s->map_skel_sz);\n\ + s->map_skel_sz = %zu; \n\ + s->maps = (struct bpf_map_skeleton *)calloc(s->map_cnt,\n\ + sizeof(*s->maps) > %zu ? sizeof(*s->maps) : %zu);\n\ if (!s->maps) { \n\ err = -ENOMEM; \n\ goto err; \n\ } \n\ ", - map_cnt + map_cnt, map_sz, map_sz, map_sz ); i = 0; bpf_object__for_each_map(map, obj) { @@ -878,23 +895,22 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped, bool codegen("\ \n\ - \n\ - s->maps[%zu].name = \"%s\"; \n\ - s->maps[%zu].map = &obj->maps.%s; \n\ + \n\ + map = (struct bpf_map_skeleton *)((char *)s->maps + %zu * s->map_skel_sz);\n\ + map->name = \"%s\"; \n\ + map->map = &obj->maps.%s; \n\ ", - i, bpf_map__name(map), i, ident); + i, bpf_map__name(map), ident); /* memory-mapped internal maps */ if (mmaped && is_mmapable_map(map, ident, sizeof(ident))) { - printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n", - i, ident); + printf("\tmap->mmaped = (void **)&obj->%s;\n", ident); } if (populate_links && bpf_map__type(map) == BPF_MAP_TYPE_STRUCT_OPS) { codegen("\ \n\ - s->maps[%zu].link = &obj->links.%s;\n\ - ", - i, ident); + map->link = &obj->links.%s; \n\ + ", ident); } i++; } @@ -1463,6 +1479,7 @@ static int do_skeleton(int argc, char **argv) %1$s__create_skeleton(struct %1$s *obj) \n\ { \n\ struct bpf_object_skeleton *s; \n\ + struct bpf_map_skeleton *map __attribute__((unused));\n\ int err; \n\ \n\ s = (struct bpf_object_skeleton *)calloc(1, sizeof(*s));\n\ @@ -1753,6 +1770,7 @@ static int do_subskeleton(int argc, char **argv) { \n\ struct %1$s *obj; \n\ struct bpf_object_subskeleton *s; \n\ + struct bpf_map_skeleton *map __attribute__((unused));\n\ int err; \n\ \n\ obj = (struct %1$s *)calloc(1, sizeof(*obj)); \n\ From 99fb9531886d8ffa0aa9a693089784c7338518a3 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Mon, 8 Jul 2024 13:45:39 -0700 Subject: [PATCH 2/3] libbpf: fix BPF skeleton forward/backward compat handling BPF skeleton was designed from day one to be extensible. Generated BPF skeleton code specifies actual sizes of map/prog/variable skeletons for that reason and libbpf is supposed to work with newer/older versions correctly. Unfortunately, it was missed that we implicitly embed hard-coded most up-to-date (according to libbpf's version of libbpf.h header used to compile BPF skeleton header) sizes of those structs, which can differ from the actual sizes at runtime when libbpf is used as a shared library. We have a few places were we just index array of maps/progs/vars, which implicitly uses these potentially invalid sizes of structs. This patch aims to fix this problem going forward. Once this lands, we'll backport these changes in Github repo to create patched releases for older libbpfs. Acked-by: Eduard Zingerman Reviewed-by: Alan Maguire Fixes: d66562fba1ce ("libbpf: Add BPF object skeleton support") Fixes: 430025e5dca5 ("libbpf: Add subskeleton scaffolding") Fixes: 08ac454e258e ("libbpf: Auto-attach struct_ops BPF maps in BPF skeleton") Co-developed-by: Mykyta Yatsenko Signed-off-by: Mykyta Yatsenko Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20240708204540.4188946-3-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- tools/lib/bpf/libbpf.c | 47 ++++++++++++++++++++++++------------------ 1 file changed, 27 insertions(+), 20 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 30f121754d83..8625c948f60a 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -13712,14 +13712,15 @@ int libbpf_num_possible_cpus(void) static int populate_skeleton_maps(const struct bpf_object *obj, struct bpf_map_skeleton *maps, - size_t map_cnt) + size_t map_cnt, size_t map_skel_sz) { int i; for (i = 0; i < map_cnt; i++) { - struct bpf_map **map = maps[i].map; - const char *name = maps[i].name; - void **mmaped = maps[i].mmaped; + struct bpf_map_skeleton *map_skel = (void *)maps + i * map_skel_sz; + struct bpf_map **map = map_skel->map; + const char *name = map_skel->name; + void **mmaped = map_skel->mmaped; *map = bpf_object__find_map_by_name(obj, name); if (!*map) { @@ -13736,13 +13737,14 @@ static int populate_skeleton_maps(const struct bpf_object *obj, static int populate_skeleton_progs(const struct bpf_object *obj, struct bpf_prog_skeleton *progs, - size_t prog_cnt) + size_t prog_cnt, size_t prog_skel_sz) { int i; for (i = 0; i < prog_cnt; i++) { - struct bpf_program **prog = progs[i].prog; - const char *name = progs[i].name; + struct bpf_prog_skeleton *prog_skel = (void *)progs + i * prog_skel_sz; + struct bpf_program **prog = prog_skel->prog; + const char *name = prog_skel->name; *prog = bpf_object__find_program_by_name(obj, name); if (!*prog) { @@ -13783,13 +13785,13 @@ int bpf_object__open_skeleton(struct bpf_object_skeleton *s, } *s->obj = obj; - err = populate_skeleton_maps(obj, s->maps, s->map_cnt); + err = populate_skeleton_maps(obj, s->maps, s->map_cnt, s->map_skel_sz); if (err) { pr_warn("failed to populate skeleton maps for '%s': %d\n", s->name, err); return libbpf_err(err); } - err = populate_skeleton_progs(obj, s->progs, s->prog_cnt); + err = populate_skeleton_progs(obj, s->progs, s->prog_cnt, s->prog_skel_sz); if (err) { pr_warn("failed to populate skeleton progs for '%s': %d\n", s->name, err); return libbpf_err(err); @@ -13819,20 +13821,20 @@ int bpf_object__open_subskeleton(struct bpf_object_subskeleton *s) return libbpf_err(-errno); } - err = populate_skeleton_maps(s->obj, s->maps, s->map_cnt); + err = populate_skeleton_maps(s->obj, s->maps, s->map_cnt, s->map_skel_sz); if (err) { pr_warn("failed to populate subskeleton maps: %d\n", err); return libbpf_err(err); } - err = populate_skeleton_progs(s->obj, s->progs, s->prog_cnt); + err = populate_skeleton_progs(s->obj, s->progs, s->prog_cnt, s->prog_skel_sz); if (err) { pr_warn("failed to populate subskeleton maps: %d\n", err); return libbpf_err(err); } for (var_idx = 0; var_idx < s->var_cnt; var_idx++) { - var_skel = &s->vars[var_idx]; + var_skel = (void *)s->vars + var_idx * s->var_skel_sz; map = *var_skel->map; map_type_id = bpf_map__btf_value_type_id(map); map_type = btf__type_by_id(btf, map_type_id); @@ -13879,10 +13881,11 @@ int bpf_object__load_skeleton(struct bpf_object_skeleton *s) } for (i = 0; i < s->map_cnt; i++) { - struct bpf_map *map = *s->maps[i].map; + struct bpf_map_skeleton *map_skel = (void *)s->maps + i * s->map_skel_sz; + struct bpf_map *map = *map_skel->map; size_t mmap_sz = bpf_map_mmap_sz(map); int prot, map_fd = map->fd; - void **mmaped = s->maps[i].mmaped; + void **mmaped = map_skel->mmaped; if (!mmaped) continue; @@ -13930,8 +13933,9 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s) int i, err; for (i = 0; i < s->prog_cnt; i++) { - struct bpf_program *prog = *s->progs[i].prog; - struct bpf_link **link = s->progs[i].link; + struct bpf_prog_skeleton *prog_skel = (void *)s->progs + i * s->prog_skel_sz; + struct bpf_program *prog = *prog_skel->prog; + struct bpf_link **link = prog_skel->link; if (!prog->autoload || !prog->autoattach) continue; @@ -13970,8 +13974,9 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s) return 0; for (i = 0; i < s->map_cnt; i++) { - struct bpf_map *map = *s->maps[i].map; - struct bpf_link **link = s->maps[i].link; + struct bpf_map_skeleton *map_skel = (void *)s->maps + i * s->map_skel_sz; + struct bpf_map *map = *map_skel->map; + struct bpf_link **link = map_skel->link; if (!map->autocreate || !map->autoattach) continue; @@ -14000,7 +14005,8 @@ void bpf_object__detach_skeleton(struct bpf_object_skeleton *s) int i; for (i = 0; i < s->prog_cnt; i++) { - struct bpf_link **link = s->progs[i].link; + struct bpf_prog_skeleton *prog_skel = (void *)s->progs + i * s->prog_skel_sz; + struct bpf_link **link = prog_skel->link; bpf_link__destroy(*link); *link = NULL; @@ -14010,7 +14016,8 @@ void bpf_object__detach_skeleton(struct bpf_object_skeleton *s) return; for (i = 0; i < s->map_cnt; i++) { - struct bpf_link **link = s->maps[i].link; + struct bpf_map_skeleton *map_skel = (void *)s->maps + i * s->map_skel_sz; + struct bpf_link **link = map_skel->link; if (link) { bpf_link__destroy(*link); From a459f4bb27f2e2730039c57786b82288742c8c74 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Mon, 8 Jul 2024 13:45:40 -0700 Subject: [PATCH 3/3] libbpf: improve old BPF skeleton handling for map auto-attach Improve how we handle old BPF skeletons when it comes to BPF map auto-attachment. Emit one warn-level message per each struct_ops map that could have been auto-attached, if user provided recent enough BPF skeleton version. Don't spam log if there are no relevant struct_ops maps, though. This should help users realize that they probably need to regenerate BPF skeleton header with more recent bpftool/libbpf-cargo (or whatever other means of BPF skeleton generation). Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman Link: https://lore.kernel.org/r/20240708204540.4188946-4-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- tools/lib/bpf/libbpf.c | 26 ++++++++++++++------------ 1 file changed, 14 insertions(+), 12 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 8625c948f60a..a3be6f8fac09 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -13967,32 +13967,34 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s) */ } - /* Skeleton is created with earlier version of bpftool - * which does not support auto-attachment - */ - if (s->map_skel_sz < sizeof(struct bpf_map_skeleton)) - return 0; for (i = 0; i < s->map_cnt; i++) { struct bpf_map_skeleton *map_skel = (void *)s->maps + i * s->map_skel_sz; struct bpf_map *map = *map_skel->map; - struct bpf_link **link = map_skel->link; + struct bpf_link **link; if (!map->autocreate || !map->autoattach) continue; - if (*link) - continue; - /* only struct_ops maps can be attached */ if (!bpf_map__is_struct_ops(map)) continue; - *link = bpf_map__attach_struct_ops(map); + /* skeleton is created with earlier version of bpftool, notify user */ + if (s->map_skel_sz < offsetofend(struct bpf_map_skeleton, link)) { + pr_warn("map '%s': BPF skeleton version is old, skipping map auto-attachment...\n", + bpf_map__name(map)); + continue; + } + + link = map_skel->link; + if (*link) + continue; + + *link = bpf_map__attach_struct_ops(map); if (!*link) { err = -errno; - pr_warn("map '%s': failed to auto-attach: %d\n", - bpf_map__name(map), err); + pr_warn("map '%s': failed to auto-attach: %d\n", bpf_map__name(map), err); return libbpf_err(err); } }