From 0de445d18e36ca5914337217c118016ba5db574d Mon Sep 17 00:00:00 2001 From: Mykyta Yatsenko Date: Mon, 17 Mar 2025 17:40:36 +0000 Subject: [PATCH 1/4] bpf: BPF token support for BPF_BTF_GET_FD_BY_ID Currently BPF_BTF_GET_FD_BY_ID requires CAP_SYS_ADMIN, which does not allow running it from user namespace. This creates a problem when freplace program running from user namespace needs to query target program BTF. This patch relaxes capable check from CAP_SYS_ADMIN to CAP_BPF and adds support for BPF token that can be passed in attributes to syscall. Signed-off-by: Mykyta Yatsenko Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250317174039.161275-2-mykyta.yatsenko5@gmail.com --- include/uapi/linux/bpf.h | 1 + kernel/bpf/syscall.c | 23 +++++++++++++++++++++-- tools/include/uapi/linux/bpf.h | 1 + 3 files changed, 23 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index bb37897c0393..661de2444965 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -1652,6 +1652,7 @@ union bpf_attr { }; __u32 next_id; __u32 open_flags; + __s32 fd_by_id_token_fd; }; struct { /* anonymous struct used by BPF_OBJ_GET_INFO_BY_FD */ diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 6a8f20ee2851..419f82c78203 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -5120,15 +5120,34 @@ static int bpf_btf_load(const union bpf_attr *attr, bpfptr_t uattr, __u32 uattr_ return btf_new_fd(attr, uattr, uattr_size); } -#define BPF_BTF_GET_FD_BY_ID_LAST_FIELD btf_id +#define BPF_BTF_GET_FD_BY_ID_LAST_FIELD fd_by_id_token_fd static int bpf_btf_get_fd_by_id(const union bpf_attr *attr) { + struct bpf_token *token = NULL; + if (CHECK_ATTR(BPF_BTF_GET_FD_BY_ID)) return -EINVAL; - if (!capable(CAP_SYS_ADMIN)) + if (attr->open_flags & ~BPF_F_TOKEN_FD) + return -EINVAL; + + if (attr->open_flags & BPF_F_TOKEN_FD) { + token = bpf_token_get_from_fd(attr->fd_by_id_token_fd); + if (IS_ERR(token)) + return PTR_ERR(token); + if (!bpf_token_allow_cmd(token, BPF_BTF_GET_FD_BY_ID)) { + bpf_token_put(token); + token = NULL; + } + } + + if (!bpf_token_capable(token, CAP_SYS_ADMIN)) { + bpf_token_put(token); return -EPERM; + } + + bpf_token_put(token); return btf_get_fd_by_id(attr->btf_id); } diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index bb37897c0393..661de2444965 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -1652,6 +1652,7 @@ union bpf_attr { }; __u32 next_id; __u32 open_flags; + __s32 fd_by_id_token_fd; }; struct { /* anonymous struct used by BPF_OBJ_GET_INFO_BY_FD */ From 07651ccda9ff10a8ca427670cdd06ce2c8e4269c Mon Sep 17 00:00:00 2001 From: Mykyta Yatsenko Date: Mon, 17 Mar 2025 17:40:37 +0000 Subject: [PATCH 2/4] bpf: Return prog btf_id without capable check Return prog's btf_id from bpf_prog_get_info_by_fd regardless of capable check. This patch enables scenario, when freplace program, running from user namespace, requires to query target prog's btf. Signed-off-by: Mykyta Yatsenko Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20250317174039.161275-3-mykyta.yatsenko5@gmail.com --- kernel/bpf/syscall.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 419f82c78203..380b445a304c 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -4732,6 +4732,8 @@ static int bpf_prog_get_info_by_fd(struct file *file, info.recursion_misses = stats.misses; info.verified_insns = prog->aux->verified_insns; + if (prog->aux->btf) + info.btf_id = btf_obj_id(prog->aux->btf); if (!bpf_capable()) { info.jited_prog_len = 0; @@ -4878,8 +4880,6 @@ static int bpf_prog_get_info_by_fd(struct file *file, } } - if (prog->aux->btf) - info.btf_id = btf_obj_id(prog->aux->btf); info.attach_btf_id = prog->aux->attach_btf_id; if (attach_btf) info.attach_btf_obj_id = btf_obj_id(attach_btf); From 974ef9f0d23edc1a802691c585b84514b414a96d Mon Sep 17 00:00:00 2001 From: Mykyta Yatsenko Date: Mon, 17 Mar 2025 17:40:38 +0000 Subject: [PATCH 3/4] libbpf: Pass BPF token from find_prog_btf_id to BPF_BTF_GET_FD_BY_ID Pass BPF token from bpf_program__set_attach_target to BPF_BTF_GET_FD_BY_ID bpf command. When freplace program attaches to target program, it needs to look up for BTF of the target, this may require BPF token, if, for example, running from user namespace. Signed-off-by: Mykyta Yatsenko Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20250317174039.161275-4-mykyta.yatsenko5@gmail.com --- tools/lib/bpf/bpf.c | 3 ++- tools/lib/bpf/bpf.h | 3 ++- tools/lib/bpf/btf.c | 15 +++++++++++++-- tools/lib/bpf/libbpf.c | 10 +++++----- tools/lib/bpf/libbpf_internal.h | 1 + 5 files changed, 23 insertions(+), 9 deletions(-) diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c index 359f73ead613..a9c3e33d0f8a 100644 --- a/tools/lib/bpf/bpf.c +++ b/tools/lib/bpf/bpf.c @@ -1097,7 +1097,7 @@ int bpf_map_get_fd_by_id(__u32 id) int bpf_btf_get_fd_by_id_opts(__u32 id, const struct bpf_get_fd_by_id_opts *opts) { - const size_t attr_sz = offsetofend(union bpf_attr, open_flags); + const size_t attr_sz = offsetofend(union bpf_attr, fd_by_id_token_fd); union bpf_attr attr; int fd; @@ -1107,6 +1107,7 @@ int bpf_btf_get_fd_by_id_opts(__u32 id, memset(&attr, 0, attr_sz); attr.btf_id = id; attr.open_flags = OPTS_GET(opts, open_flags, 0); + attr.fd_by_id_token_fd = OPTS_GET(opts, token_fd, 0); fd = sys_bpf_fd(BPF_BTF_GET_FD_BY_ID, &attr, attr_sz); return libbpf_err_errno(fd); diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h index 435da95d2058..777627d33d25 100644 --- a/tools/lib/bpf/bpf.h +++ b/tools/lib/bpf/bpf.h @@ -487,9 +487,10 @@ LIBBPF_API int bpf_link_get_next_id(__u32 start_id, __u32 *next_id); struct bpf_get_fd_by_id_opts { size_t sz; /* size of this struct for forward/backward compatibility */ __u32 open_flags; /* permissions requested for the operation on fd */ + __u32 token_fd; size_t :0; }; -#define bpf_get_fd_by_id_opts__last_field open_flags +#define bpf_get_fd_by_id_opts__last_field token_fd LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id); LIBBPF_API int bpf_prog_get_fd_by_id_opts(__u32 id, diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index eea99c766a20..38bc6b14b066 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -1619,12 +1619,18 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf) return btf; } -struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf) +struct btf *btf_load_from_kernel(__u32 id, struct btf *base_btf, int token_fd) { struct btf *btf; int btf_fd; + LIBBPF_OPTS(bpf_get_fd_by_id_opts, opts); - btf_fd = bpf_btf_get_fd_by_id(id); + if (token_fd) { + opts.open_flags |= BPF_F_TOKEN_FD; + opts.token_fd = token_fd; + } + + btf_fd = bpf_btf_get_fd_by_id_opts(id, &opts); if (btf_fd < 0) return libbpf_err_ptr(-errno); @@ -1634,6 +1640,11 @@ struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf) return libbpf_ptr(btf); } +struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf) +{ + return btf_load_from_kernel(id, base_btf, 0); +} + struct btf *btf__load_from_kernel_by_id(__u32 id) { return btf__load_from_kernel_by_id_split(id, NULL); diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 8e32286854ef..6b85060f07b3 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -10024,7 +10024,7 @@ int libbpf_find_vmlinux_btf_id(const char *name, return libbpf_err(err); } -static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd) +static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd, int token_fd) { struct bpf_prog_info info; __u32 info_len = sizeof(info); @@ -10044,7 +10044,7 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd) pr_warn("The target program doesn't have BTF\n"); goto out; } - btf = btf__load_from_kernel_by_id(info.btf_id); + btf = btf_load_from_kernel(info.btf_id, NULL, token_fd); err = libbpf_get_error(btf); if (err) { pr_warn("Failed to get BTF %d of the program: %s\n", info.btf_id, errstr(err)); @@ -10127,7 +10127,7 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attac pr_warn("prog '%s': attach program FD is not set\n", prog->name); return -EINVAL; } - err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd); + err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd, prog->obj->token_fd); if (err < 0) { pr_warn("prog '%s': failed to find BPF program (FD %d) BTF ID for '%s': %s\n", prog->name, attach_prog_fd, attach_name, errstr(err)); @@ -12923,7 +12923,7 @@ struct bpf_link *bpf_program__attach_freplace(const struct bpf_program *prog, if (target_fd) { LIBBPF_OPTS(bpf_link_create_opts, target_opts); - btf_id = libbpf_find_prog_btf_id(attach_func_name, target_fd); + btf_id = libbpf_find_prog_btf_id(attach_func_name, target_fd, prog->obj->token_fd); if (btf_id < 0) return libbpf_err_ptr(btf_id); @@ -13744,7 +13744,7 @@ int bpf_program__set_attach_target(struct bpf_program *prog, if (attach_prog_fd) { btf_id = libbpf_find_prog_btf_id(attach_func_name, - attach_prog_fd); + attach_prog_fd, prog->obj->token_fd); if (btf_id < 0) return libbpf_err(btf_id); } else { diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h index de498e2dd6b0..76669c73dcd1 100644 --- a/tools/lib/bpf/libbpf_internal.h +++ b/tools/lib/bpf/libbpf_internal.h @@ -409,6 +409,7 @@ int libbpf__load_raw_btf(const char *raw_types, size_t types_len, int btf_load_into_kernel(struct btf *btf, char *log_buf, size_t log_sz, __u32 log_level, int token_fd); +struct btf *btf_load_from_kernel(__u32 id, struct btf *base_btf, int token_fd); struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf); void btf_get_kernel_prefix_kind(enum bpf_attach_type attach_type, From a024843d92cca491034dac648bcfec967199a4a4 Mon Sep 17 00:00:00 2001 From: Mykyta Yatsenko Date: Mon, 17 Mar 2025 17:40:39 +0000 Subject: [PATCH 4/4] selftests/bpf: Test freplace from user namespace Add selftests to verify that it is possible to load freplace program from user namespace if BPF token is initialized by bpf_object__prepare before calling bpf_program__set_attach_target. Negative test is added as well. Modified type of the priv_prog to xdp, as kprobe did not work on aarch64 and s390x. Signed-off-by: Mykyta Yatsenko Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20250317174039.161275-5-mykyta.yatsenko5@gmail.com --- .../testing/selftests/bpf/prog_tests/token.c | 97 ++++++++++++++++++- .../selftests/bpf/progs/priv_freplace_prog.c | 13 +++ tools/testing/selftests/bpf/progs/priv_prog.c | 6 +- 3 files changed, 112 insertions(+), 4 deletions(-) create mode 100644 tools/testing/selftests/bpf/progs/priv_freplace_prog.c diff --git a/tools/testing/selftests/bpf/prog_tests/token.c b/tools/testing/selftests/bpf/prog_tests/token.c index c3ab9b6fb069..f9392df23f8a 100644 --- a/tools/testing/selftests/bpf/prog_tests/token.c +++ b/tools/testing/selftests/bpf/prog_tests/token.c @@ -19,6 +19,7 @@ #include "priv_prog.skel.h" #include "dummy_st_ops_success.skel.h" #include "token_lsm.skel.h" +#include "priv_freplace_prog.skel.h" static inline int sys_mount(const char *dev_name, const char *dir_name, const char *type, unsigned long flags, @@ -788,6 +789,84 @@ static int userns_obj_priv_prog(int mnt_fd, struct token_lsm *lsm_skel) return 0; } +static int userns_obj_priv_freplace_setup(int mnt_fd, struct priv_freplace_prog **fr_skel, + struct priv_prog **skel, int *tgt_fd) +{ + LIBBPF_OPTS(bpf_object_open_opts, opts); + int err; + char buf[256]; + + /* use bpf_token_path to provide BPF FS path */ + snprintf(buf, sizeof(buf), "/proc/self/fd/%d", mnt_fd); + opts.bpf_token_path = buf; + *skel = priv_prog__open_opts(&opts); + if (!ASSERT_OK_PTR(*skel, "priv_prog__open_opts")) + return -EINVAL; + err = priv_prog__load(*skel); + if (!ASSERT_OK(err, "priv_prog__load")) + return -EINVAL; + + *fr_skel = priv_freplace_prog__open_opts(&opts); + if (!ASSERT_OK_PTR(*skel, "priv_freplace_prog__open_opts")) + return -EINVAL; + + *tgt_fd = bpf_program__fd((*skel)->progs.xdp_prog1); + return 0; +} + +/* Verify that freplace works from user namespace, because bpf token is loaded + * in bpf_object__prepare + */ +static int userns_obj_priv_freplace_prog(int mnt_fd, struct token_lsm *lsm_skel) +{ + struct priv_freplace_prog *fr_skel = NULL; + struct priv_prog *skel = NULL; + int err, tgt_fd; + + err = userns_obj_priv_freplace_setup(mnt_fd, &fr_skel, &skel, &tgt_fd); + if (!ASSERT_OK(err, "setup")) + goto out; + + err = bpf_object__prepare(fr_skel->obj); + if (!ASSERT_OK(err, "freplace__prepare")) + goto out; + + err = bpf_program__set_attach_target(fr_skel->progs.new_xdp_prog2, tgt_fd, "xdp_prog1"); + if (!ASSERT_OK(err, "set_attach_target")) + goto out; + + err = priv_freplace_prog__load(fr_skel); + ASSERT_OK(err, "priv_freplace_prog__load"); + +out: + priv_freplace_prog__destroy(fr_skel); + priv_prog__destroy(skel); + return err; +} + +/* Verify that replace fails to set attach target from user namespace without bpf token */ +static int userns_obj_priv_freplace_prog_fail(int mnt_fd, struct token_lsm *lsm_skel) +{ + struct priv_freplace_prog *fr_skel = NULL; + struct priv_prog *skel = NULL; + int err, tgt_fd; + + err = userns_obj_priv_freplace_setup(mnt_fd, &fr_skel, &skel, &tgt_fd); + if (!ASSERT_OK(err, "setup")) + goto out; + + err = bpf_program__set_attach_target(fr_skel->progs.new_xdp_prog2, tgt_fd, "xdp_prog1"); + if (ASSERT_ERR(err, "attach fails")) + err = 0; + else + err = -EINVAL; + +out: + priv_freplace_prog__destroy(fr_skel); + priv_prog__destroy(skel); + return err; +} + /* this test is called with BPF FS that doesn't delegate BPF_BTF_LOAD command, * which should cause struct_ops application to fail, as BTF won't be uploaded * into the kernel, even if STRUCT_OPS programs themselves are allowed @@ -1004,12 +1083,28 @@ void test_token(void) if (test__start_subtest("obj_priv_prog")) { struct bpffs_opts opts = { .cmds = bit(BPF_PROG_LOAD), - .progs = bit(BPF_PROG_TYPE_KPROBE), + .progs = bit(BPF_PROG_TYPE_XDP), .attachs = ~0ULL, }; subtest_userns(&opts, userns_obj_priv_prog); } + if (test__start_subtest("obj_priv_freplace_prog")) { + struct bpffs_opts opts = { + .cmds = bit(BPF_BTF_LOAD) | bit(BPF_PROG_LOAD) | bit(BPF_BTF_GET_FD_BY_ID), + .progs = bit(BPF_PROG_TYPE_EXT) | bit(BPF_PROG_TYPE_XDP), + .attachs = ~0ULL, + }; + subtest_userns(&opts, userns_obj_priv_freplace_prog); + } + if (test__start_subtest("obj_priv_freplace_prog_fail")) { + struct bpffs_opts opts = { + .cmds = bit(BPF_BTF_LOAD) | bit(BPF_PROG_LOAD) | bit(BPF_BTF_GET_FD_BY_ID), + .progs = bit(BPF_PROG_TYPE_EXT) | bit(BPF_PROG_TYPE_XDP), + .attachs = ~0ULL, + }; + subtest_userns(&opts, userns_obj_priv_freplace_prog_fail); + } if (test__start_subtest("obj_priv_btf_fail")) { struct bpffs_opts opts = { /* disallow BTF loading */ diff --git a/tools/testing/selftests/bpf/progs/priv_freplace_prog.c b/tools/testing/selftests/bpf/progs/priv_freplace_prog.c new file mode 100644 index 000000000000..ccf1b04010ba --- /dev/null +++ b/tools/testing/selftests/bpf/progs/priv_freplace_prog.c @@ -0,0 +1,13 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */ + +#include "vmlinux.h" +#include + +char _license[] SEC("license") = "GPL"; + +SEC("freplace/xdp_prog1") +int new_xdp_prog2(struct xdp_md *xd) +{ + return XDP_DROP; +} diff --git a/tools/testing/selftests/bpf/progs/priv_prog.c b/tools/testing/selftests/bpf/progs/priv_prog.c index 3c7b2b618c8a..725e29595079 100644 --- a/tools/testing/selftests/bpf/progs/priv_prog.c +++ b/tools/testing/selftests/bpf/progs/priv_prog.c @@ -6,8 +6,8 @@ char _license[] SEC("license") = "GPL"; -SEC("kprobe") -int kprobe_prog(void *ctx) +SEC("xdp") +int xdp_prog1(struct xdp_md *xdp) { - return 1; + return XDP_DROP; }