From e10500b69c3f3378f3dcfc8c2fe4cdb74fc844f5 Mon Sep 17 00:00:00 2001 From: Quentin Monnet Date: Thu, 5 Dec 2024 13:59:42 +0000 Subject: libbpf: Fix segfault due to libelf functions not setting errno Libelf functions do not set errno on failure. Instead, it relies on its internal _elf_errno value, that can be retrieved via elf_errno (or the corresponding message via elf_errmsg()). From "man libelf": If a libelf function encounters an error it will set an internal error code that can be retrieved with elf_errno. Each thread maintains its own separate error code. The meaning of each error code can be determined with elf_errmsg, which returns a string describing the error. As a consequence, libbpf should not return -errno when a function from libelf fails, because an empty value will not be interpreted as an error and won't prevent the program to stop. This is visible in bpf_linker__add_file(), for example, where we call a succession of functions that rely on libelf: err = err ?: linker_load_obj_file(linker, filename, opts, &obj); err = err ?: linker_append_sec_data(linker, &obj); err = err ?: linker_append_elf_syms(linker, &obj); err = err ?: linker_append_elf_relos(linker, &obj); err = err ?: linker_append_btf(linker, &obj); err = err ?: linker_append_btf_ext(linker, &obj); If the object file that we try to process is not, in fact, a correct object file, linker_load_obj_file() may fail with errno not being set, and return 0. In this case we attempt to run linker_append_elf_sysms() and may segfault. This can happen (and was discovered) with bpftool: $ bpftool gen object output.o sample_ret0.bpf.c libbpf: failed to get ELF header for sample_ret0.bpf.c: invalid `Elf' handle zsh: segmentation fault (core dumped) bpftool gen object output.o sample_ret0.bpf.c Fix the issue by returning a non-null error code (-EINVAL) when libelf functions fail. Fixes: faf6ed321cf6 ("libbpf: Add BPF static linker APIs") Signed-off-by: Quentin Monnet Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20241205135942.65262-1-qmo@kernel.org --- tools/lib/bpf/linker.c | 22 ++++++++-------------- 1 file changed, 8 insertions(+), 14 deletions(-) (limited to 'tools/lib/bpf/linker.c') diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c index cf71d149fe26..e56ba6e67451 100644 --- a/tools/lib/bpf/linker.c +++ b/tools/lib/bpf/linker.c @@ -566,17 +566,15 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, } obj->elf = elf_begin(obj->fd, ELF_C_READ_MMAP, NULL); if (!obj->elf) { - err = -errno; pr_warn_elf("failed to parse ELF file '%s'", filename); - return err; + return -EINVAL; } /* Sanity check ELF file high-level properties */ ehdr = elf64_getehdr(obj->elf); if (!ehdr) { - err = -errno; pr_warn_elf("failed to get ELF header for %s", filename); - return err; + return -EINVAL; } /* Linker output endianness set by first input object */ @@ -606,9 +604,8 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, } if (elf_getshdrstrndx(obj->elf, &obj->shstrs_sec_idx)) { - err = -errno; pr_warn_elf("failed to get SHSTRTAB section index for %s", filename); - return err; + return -EINVAL; } scn = NULL; @@ -618,26 +615,23 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, shdr = elf64_getshdr(scn); if (!shdr) { - err = -errno; pr_warn_elf("failed to get section #%zu header for %s", sec_idx, filename); - return err; + return -EINVAL; } sec_name = elf_strptr(obj->elf, obj->shstrs_sec_idx, shdr->sh_name); if (!sec_name) { - err = -errno; pr_warn_elf("failed to get section #%zu name for %s", sec_idx, filename); - return err; + return -EINVAL; } data = elf_getdata(scn, 0); if (!data) { - err = -errno; pr_warn_elf("failed to get section #%zu (%s) data from %s", sec_idx, sec_name, filename); - return err; + return -EINVAL; } sec = add_src_sec(obj, sec_name); @@ -2680,14 +2674,14 @@ int bpf_linker__finalize(struct bpf_linker *linker) /* Finalize ELF layout */ if (elf_update(linker->elf, ELF_C_NULL) < 0) { - err = -errno; + err = -EINVAL; pr_warn_elf("failed to finalize ELF layout"); return libbpf_err(err); } /* Write out final ELF contents */ if (elf_update(linker->elf, ELF_C_WRITE) < 0) { - err = -errno; + err = -EINVAL; pr_warn_elf("failed to write ELF contents"); return libbpf_err(err); } -- cgit v1.2.3 From b641712925bfe89ff7217cc2d0b7a8e042df556b Mon Sep 17 00:00:00 2001 From: Alastair Robertson Date: Wed, 11 Dec 2024 08:40:29 -0800 Subject: libbpf: Pull file-opening logic up to top-level functions Move the filename arguments and file-descriptor handling from init_output_elf() and linker_load_obj_file() and instead handle them at the top-level in bpf_linker__new() and bpf_linker__add_file(). This will allow the inner functions to be shared with a new, non-filename-based, API in the next commit. Signed-off-by: Alastair Robertson Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20241211164030.573042-2-ajor@meta.com --- tools/lib/bpf/linker.c | 84 +++++++++++++++++++++++++------------------------- 1 file changed, 42 insertions(+), 42 deletions(-) (limited to 'tools/lib/bpf/linker.c') diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c index e56ba6e67451..c49e94506d9c 100644 --- a/tools/lib/bpf/linker.c +++ b/tools/lib/bpf/linker.c @@ -157,10 +157,9 @@ struct bpf_linker { #define pr_warn_elf(fmt, ...) \ libbpf_print(LIBBPF_WARN, "libbpf: " fmt ": %s\n", ##__VA_ARGS__, elf_errmsg(-1)) -static int init_output_elf(struct bpf_linker *linker, const char *file); +static int init_output_elf(struct bpf_linker *linker); -static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, - const struct bpf_linker_file_opts *opts, +static int linker_load_obj_file(struct bpf_linker *linker, struct src_obj *obj); static int linker_sanity_check_elf(struct src_obj *obj); static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec); @@ -233,9 +232,20 @@ struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts if (!linker) return errno = ENOMEM, NULL; - linker->fd = -1; + linker->filename = strdup(filename); + if (!linker->filename) { + err = -ENOMEM; + goto err_out; + } + + linker->fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644); + if (linker->fd < 0) { + err = -errno; + pr_warn("failed to create '%s': %d\n", filename, err); + goto err_out; + } - err = init_output_elf(linker, filename); + err = init_output_elf(linker); if (err) goto err_out; @@ -294,23 +304,12 @@ static Elf64_Sym *add_new_sym(struct bpf_linker *linker, size_t *sym_idx) return sym; } -static int init_output_elf(struct bpf_linker *linker, const char *file) +static int init_output_elf(struct bpf_linker *linker) { int err, str_off; Elf64_Sym *init_sym; struct dst_sec *sec; - linker->filename = strdup(file); - if (!linker->filename) - return -ENOMEM; - - linker->fd = open(file, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644); - if (linker->fd < 0) { - err = -errno; - pr_warn("failed to create '%s': %s\n", file, errstr(err)); - return err; - } - linker->elf = elf_begin(linker->fd, ELF_C_WRITE, NULL); if (!linker->elf) { pr_warn_elf("failed to create ELF object"); @@ -440,7 +439,7 @@ int bpf_linker__add_file(struct bpf_linker *linker, const char *filename, const struct bpf_linker_file_opts *opts) { struct src_obj obj = {}; - int err = 0; + int err = 0, fd; if (!OPTS_VALID(opts, bpf_linker_file_opts)) return libbpf_err(-EINVAL); @@ -448,7 +447,17 @@ int bpf_linker__add_file(struct bpf_linker *linker, const char *filename, if (!linker->elf) return libbpf_err(-EINVAL); - err = err ?: linker_load_obj_file(linker, filename, opts, &obj); + fd = open(filename, O_RDONLY | O_CLOEXEC); + if (fd < 0) { + err = -errno; + pr_warn("failed to open file '%s': %s\n", filename, errstr(err)); + return libbpf_err(err); + } + + obj.filename = filename; + obj.fd = fd; + + err = err ?: linker_load_obj_file(linker, &obj); err = err ?: linker_append_sec_data(linker, &obj); err = err ?: linker_append_elf_syms(linker, &obj); err = err ?: linker_append_elf_relos(linker, &obj); @@ -534,8 +543,7 @@ static struct src_sec *add_src_sec(struct src_obj *obj, const char *sec_name) return sec; } -static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, - const struct bpf_linker_file_opts *opts, +static int linker_load_obj_file(struct bpf_linker *linker, struct src_obj *obj) { int err = 0; @@ -554,26 +562,18 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, #error "Unknown __BYTE_ORDER__" #endif - pr_debug("linker: adding object file '%s'...\n", filename); - - obj->filename = filename; + pr_debug("linker: adding object file '%s'...\n", obj->filename); - obj->fd = open(filename, O_RDONLY | O_CLOEXEC); - if (obj->fd < 0) { - err = -errno; - pr_warn("failed to open file '%s': %s\n", filename, errstr(err)); - return err; - } obj->elf = elf_begin(obj->fd, ELF_C_READ_MMAP, NULL); if (!obj->elf) { - pr_warn_elf("failed to parse ELF file '%s'", filename); + pr_warn_elf("failed to parse ELF file '%s'", obj->filename); return -EINVAL; } /* Sanity check ELF file high-level properties */ ehdr = elf64_getehdr(obj->elf); if (!ehdr) { - pr_warn_elf("failed to get ELF header for %s", filename); + pr_warn_elf("failed to get ELF header for %s", obj->filename); return -EINVAL; } @@ -581,7 +581,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, obj_byteorder = ehdr->e_ident[EI_DATA]; if (obj_byteorder != ELFDATA2LSB && obj_byteorder != ELFDATA2MSB) { err = -EOPNOTSUPP; - pr_warn("unknown byte order of ELF file %s\n", filename); + pr_warn("unknown byte order of ELF file %s\n", obj->filename); return err; } if (link_byteorder == ELFDATANONE) { @@ -591,7 +591,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, obj_byteorder == ELFDATA2MSB ? "big" : "little"); } else if (link_byteorder != obj_byteorder) { err = -EOPNOTSUPP; - pr_warn("byte order mismatch with ELF file %s\n", filename); + pr_warn("byte order mismatch with ELF file %s\n", obj->filename); return err; } @@ -599,12 +599,12 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, || ehdr->e_machine != EM_BPF || ehdr->e_ident[EI_CLASS] != ELFCLASS64) { err = -EOPNOTSUPP; - pr_warn_elf("unsupported kind of ELF file %s", filename); + pr_warn_elf("unsupported kind of ELF file %s", obj->filename); return err; } if (elf_getshdrstrndx(obj->elf, &obj->shstrs_sec_idx)) { - pr_warn_elf("failed to get SHSTRTAB section index for %s", filename); + pr_warn_elf("failed to get SHSTRTAB section index for %s", obj->filename); return -EINVAL; } @@ -616,21 +616,21 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, shdr = elf64_getshdr(scn); if (!shdr) { pr_warn_elf("failed to get section #%zu header for %s", - sec_idx, filename); + sec_idx, obj->filename); return -EINVAL; } sec_name = elf_strptr(obj->elf, obj->shstrs_sec_idx, shdr->sh_name); if (!sec_name) { pr_warn_elf("failed to get section #%zu name for %s", - sec_idx, filename); + sec_idx, obj->filename); return -EINVAL; } data = elf_getdata(scn, 0); if (!data) { pr_warn_elf("failed to get section #%zu (%s) data from %s", - sec_idx, sec_name, filename); + sec_idx, sec_name, obj->filename); return -EINVAL; } @@ -666,7 +666,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, err = libbpf_get_error(obj->btf); if (err) { pr_warn("failed to parse .BTF from %s: %s\n", - filename, errstr(err)); + obj->filename, errstr(err)); return err; } sec->skipped = true; @@ -677,7 +677,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, err = libbpf_get_error(obj->btf_ext); if (err) { pr_warn("failed to parse .BTF.ext from '%s': %s\n", - filename, errstr(err)); + obj->filename, errstr(err)); return err; } sec->skipped = true; @@ -694,7 +694,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, break; default: pr_warn("unrecognized section #%zu (%s) in %s\n", - sec_idx, sec_name, filename); + sec_idx, sec_name, obj->filename); err = -EINVAL; return err; } -- cgit v1.2.3 From 6d5e5e5d7ce134a0b334c3bfe44a9326d8c5f32b Mon Sep 17 00:00:00 2001 From: Alastair Robertson Date: Wed, 11 Dec 2024 08:40:30 -0800 Subject: libbpf: Extend linker API to support in-memory ELF files The new_fd and add_fd functions correspond to the original new and add_file functions, but accept an FD instead of a file name. This gives API consumers the option of using anonymous files/memfds to avoid writing ELFs to disk. This new API will be useful for performing linking as part of bpftrace's JIT compilation. The add_buf function is a convenience wrapper that does the work of creating a memfd for the caller. Signed-off-by: Alastair Robertson Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20241211164030.573042-3-ajor@meta.com --- tools/lib/bpf/libbpf.h | 5 ++ tools/lib/bpf/libbpf.map | 4 ++ tools/lib/bpf/linker.c | 162 +++++++++++++++++++++++++++++++++++++++++------ 3 files changed, 150 insertions(+), 21 deletions(-) (limited to 'tools/lib/bpf/linker.c') diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index b2ce3a72b11d..d45807103565 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -1796,9 +1796,14 @@ struct bpf_linker_file_opts { struct bpf_linker; LIBBPF_API struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts *opts); +LIBBPF_API struct bpf_linker *bpf_linker__new_fd(int fd, struct bpf_linker_opts *opts); LIBBPF_API int bpf_linker__add_file(struct bpf_linker *linker, const char *filename, const struct bpf_linker_file_opts *opts); +LIBBPF_API int bpf_linker__add_fd(struct bpf_linker *linker, int fd, + const struct bpf_linker_file_opts *opts); +LIBBPF_API int bpf_linker__add_buf(struct bpf_linker *linker, void *buf, size_t buf_sz, + const struct bpf_linker_file_opts *opts); LIBBPF_API int bpf_linker__finalize(struct bpf_linker *linker); LIBBPF_API void bpf_linker__free(struct bpf_linker *linker); diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map index 54b6f312cfa8..a8b2936a1646 100644 --- a/tools/lib/bpf/libbpf.map +++ b/tools/lib/bpf/libbpf.map @@ -432,4 +432,8 @@ LIBBPF_1.5.0 { } LIBBPF_1.4.0; LIBBPF_1.6.0 { + global: + bpf_linker__add_buf; + bpf_linker__add_fd; + bpf_linker__new_fd; } LIBBPF_1.5.0; diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c index c49e94506d9c..b52f71c59616 100644 --- a/tools/lib/bpf/linker.c +++ b/tools/lib/bpf/linker.c @@ -4,6 +4,10 @@ * * Copyright (c) 2021 Facebook */ +#ifndef _GNU_SOURCE +#define _GNU_SOURCE +#endif + #include #include #include @@ -16,6 +20,7 @@ #include #include #include +#include #include "libbpf.h" #include "btf.h" #include "libbpf_internal.h" @@ -152,6 +157,8 @@ struct bpf_linker { /* global (including extern) ELF symbols */ int glob_sym_cnt; struct glob_sym *glob_syms; + + bool fd_is_owned; }; #define pr_warn_elf(fmt, ...) \ @@ -159,6 +166,9 @@ struct bpf_linker { static int init_output_elf(struct bpf_linker *linker); +static int bpf_linker_add_file(struct bpf_linker *linker, int fd, + const char *filename); + static int linker_load_obj_file(struct bpf_linker *linker, struct src_obj *obj); static int linker_sanity_check_elf(struct src_obj *obj); @@ -190,7 +200,7 @@ void bpf_linker__free(struct bpf_linker *linker) if (linker->elf) elf_end(linker->elf); - if (linker->fd >= 0) + if (linker->fd >= 0 && linker->fd_is_owned) close(linker->fd); strset__free(linker->strtab_strs); @@ -244,6 +254,49 @@ struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts pr_warn("failed to create '%s': %d\n", filename, err); goto err_out; } + linker->fd_is_owned = true; + + err = init_output_elf(linker); + if (err) + goto err_out; + + return linker; + +err_out: + bpf_linker__free(linker); + return errno = -err, NULL; +} + +struct bpf_linker *bpf_linker__new_fd(int fd, struct bpf_linker_opts *opts) +{ + struct bpf_linker *linker; + char filename[32]; + int err; + + if (fd < 0) + return errno = EINVAL, NULL; + + if (!OPTS_VALID(opts, bpf_linker_opts)) + return errno = EINVAL, NULL; + + if (elf_version(EV_CURRENT) == EV_NONE) { + pr_warn_elf("libelf initialization failed"); + return errno = EINVAL, NULL; + } + + linker = calloc(1, sizeof(*linker)); + if (!linker) + return errno = ENOMEM, NULL; + + snprintf(filename, sizeof(filename), "fd:%d", fd); + linker->filename = strdup(filename); + if (!linker->filename) { + err = -ENOMEM; + goto err_out; + } + + linker->fd = fd; + linker->fd_is_owned = false; err = init_output_elf(linker); if (err) @@ -435,24 +488,11 @@ static int init_output_elf(struct bpf_linker *linker) return 0; } -int bpf_linker__add_file(struct bpf_linker *linker, const char *filename, - const struct bpf_linker_file_opts *opts) +static int bpf_linker_add_file(struct bpf_linker *linker, int fd, + const char *filename) { struct src_obj obj = {}; - int err = 0, fd; - - if (!OPTS_VALID(opts, bpf_linker_file_opts)) - return libbpf_err(-EINVAL); - - if (!linker->elf) - return libbpf_err(-EINVAL); - - fd = open(filename, O_RDONLY | O_CLOEXEC); - if (fd < 0) { - err = -errno; - pr_warn("failed to open file '%s': %s\n", filename, errstr(err)); - return libbpf_err(err); - } + int err = 0; obj.filename = filename; obj.fd = fd; @@ -472,12 +512,91 @@ int bpf_linker__add_file(struct bpf_linker *linker, const char *filename, free(obj.sym_map); if (obj.elf) elf_end(obj.elf); - if (obj.fd >= 0) - close(obj.fd); + return err; +} + +int bpf_linker__add_file(struct bpf_linker *linker, const char *filename, + const struct bpf_linker_file_opts *opts) +{ + int fd, err; + + if (!OPTS_VALID(opts, bpf_linker_file_opts)) + return libbpf_err(-EINVAL); + + if (!linker->elf) + return libbpf_err(-EINVAL); + + fd = open(filename, O_RDONLY | O_CLOEXEC); + if (fd < 0) { + err = -errno; + pr_warn("failed to open file '%s': %s\n", filename, errstr(err)); + return libbpf_err(err); + } + + err = bpf_linker_add_file(linker, fd, filename); + close(fd); return libbpf_err(err); } +int bpf_linker__add_fd(struct bpf_linker *linker, int fd, + const struct bpf_linker_file_opts *opts) +{ + char filename[32]; + int err; + + if (!OPTS_VALID(opts, bpf_linker_file_opts)) + return libbpf_err(-EINVAL); + + if (!linker->elf) + return libbpf_err(-EINVAL); + + if (fd < 0) + return libbpf_err(-EINVAL); + + snprintf(filename, sizeof(filename), "fd:%d", fd); + err = bpf_linker_add_file(linker, fd, filename); + return libbpf_err(err); +} + +int bpf_linker__add_buf(struct bpf_linker *linker, void *buf, size_t buf_sz, + const struct bpf_linker_file_opts *opts) +{ + char filename[32]; + int fd, written, ret; + + if (!OPTS_VALID(opts, bpf_linker_file_opts)) + return libbpf_err(-EINVAL); + + if (!linker->elf) + return libbpf_err(-EINVAL); + + snprintf(filename, sizeof(filename), "mem:%p+%zu", buf, buf_sz); + + fd = memfd_create(filename, 0); + if (fd < 0) { + ret = -errno; + pr_warn("failed to create memfd '%s': %s\n", filename, errstr(ret)); + return libbpf_err(ret); + } + + written = 0; + while (written < buf_sz) { + ret = write(fd, buf, buf_sz); + if (ret < 0) { + ret = -errno; + pr_warn("failed to write '%s': %s\n", filename, errstr(ret)); + goto err_out; + } + written += ret; + } + + ret = bpf_linker_add_file(linker, fd, filename); +err_out: + close(fd); + return libbpf_err(ret); +} + static bool is_dwarf_sec_name(const char *name) { /* approximation, but the actual list is too long */ @@ -2687,9 +2806,10 @@ int bpf_linker__finalize(struct bpf_linker *linker) } elf_end(linker->elf); - close(linker->fd); - linker->elf = NULL; + + if (linker->fd_is_owned) + close(linker->fd); linker->fd = -1; return 0; -- cgit v1.2.3