From bb7fa09399b937cdc4432ac99f9748f5a7f69389 Mon Sep 17 00:00:00 2001 From: Hengqi Chen Date: Mon, 18 Sep 2023 02:48:12 +0000 Subject: [PATCH] libbpf: Support symbol versioning for uprobe In current implementation, we assume that symbol found in .dynsym section would have a version suffix and use it to compare with symbol user supplied. According to the spec ([0]), this assumption is incorrect, the version info of dynamic symbols are stored in .gnu.version and .gnu.version_d sections of ELF objects. For example: $ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock 000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5 000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34 000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5 $ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock 706: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 __pthread_rwlock_wrlock@GLIBC_2.2.5 2568: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@@GLIBC_2.34 2571: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@GLIBC_2.2.5 In this case, specify pthread_rwlock_wrlock@@GLIBC_2.34 or pthread_rwlock_wrlock@GLIBC_2.2.5 in bpf_uprobe_opts::func_name won't work. Because the qualified name does NOT match `pthread_rwlock_wrlock` (without version suffix) in .dynsym sections. This commit implements the symbol versioning for dynsym and allows user to specify symbol in the following forms: - func - func@LIB_VERSION - func@@LIB_VERSION In case of symbol conflicts, error out and users should resolve it by specifying a qualified name. [0]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/symversion.html Signed-off-by: Hengqi Chen Signed-off-by: Andrii Nakryiko Reviewed-by: Alan Maguire Acked-by: Jiri Olsa Link: https://lore.kernel.org/bpf/20230918024813.237475-3-hengqi.chen@gmail.com --- tools/lib/bpf/elf.c | 134 +++++++++++++++++++++++++++++++++++++---- tools/lib/bpf/libbpf.c | 2 +- 2 files changed, 124 insertions(+), 12 deletions(-) diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c index 5c9e588b17da..2a158e8a8b7c 100644 --- a/tools/lib/bpf/elf.c +++ b/tools/lib/bpf/elf.c @@ -1,5 +1,8 @@ // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) +#ifndef _GNU_SOURCE +#define _GNU_SOURCE +#endif #include #include #include @@ -10,6 +13,17 @@ #define STRERR_BUFSIZE 128 +/* A SHT_GNU_versym section holds 16-bit words. This bit is set if + * the symbol is hidden and can only be seen when referenced using an + * explicit version number. This is a GNU extension. + */ +#define VERSYM_HIDDEN 0x8000 + +/* This is the mask for the rest of the data in a word read from a + * SHT_GNU_versym section. + */ +#define VERSYM_VERSION 0x7fff + int elf_open(const char *binary_path, struct elf_fd *elf_fd) { char errmsg[STRERR_BUFSIZE]; @@ -64,13 +78,18 @@ struct elf_sym { const char *name; GElf_Sym sym; GElf_Shdr sh; + int ver; + bool hidden; }; struct elf_sym_iter { Elf *elf; Elf_Data *syms; + Elf_Data *versyms; + Elf_Data *verdefs; size_t nr_syms; size_t strtabidx; + size_t verdef_strtabidx; size_t next_sym_idx; struct elf_sym sym; int st_type; @@ -111,6 +130,26 @@ static int elf_sym_iter_new(struct elf_sym_iter *iter, iter->nr_syms = iter->syms->d_size / sh.sh_entsize; iter->elf = elf; iter->st_type = st_type; + + /* Version symbol table is meaningful to dynsym only */ + if (sh_type != SHT_DYNSYM) + return 0; + + scn = elf_find_next_scn_by_type(elf, SHT_GNU_versym, NULL); + if (!scn) + return 0; + iter->versyms = elf_getdata(scn, 0); + + scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL); + if (!scn) { + pr_debug("elf: failed to find verdef ELF sections in '%s'\n", binary_path); + return -ENOENT; + } + if (!gelf_getshdr(scn, &sh)) + return -EINVAL; + iter->verdef_strtabidx = sh.sh_link; + iter->verdefs = elf_getdata(scn, 0); + return 0; } @@ -119,6 +158,7 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter) struct elf_sym *ret = &iter->sym; GElf_Sym *sym = &ret->sym; const char *name = NULL; + GElf_Versym versym; Elf_Scn *sym_scn; size_t idx; @@ -138,12 +178,80 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter) iter->next_sym_idx = idx + 1; ret->name = name; + ret->ver = 0; + ret->hidden = false; + + if (iter->versyms) { + if (!gelf_getversym(iter->versyms, idx, &versym)) + continue; + ret->ver = versym & VERSYM_VERSION; + ret->hidden = versym & VERSYM_HIDDEN; + } return ret; } return NULL; } +static const char *elf_get_vername(struct elf_sym_iter *iter, int ver) +{ + GElf_Verdaux verdaux; + GElf_Verdef verdef; + int offset; + + offset = 0; + while (gelf_getverdef(iter->verdefs, offset, &verdef)) { + if (verdef.vd_ndx != ver) { + if (!verdef.vd_next) + break; + + offset += verdef.vd_next; + continue; + } + + if (!gelf_getverdaux(iter->verdefs, offset + verdef.vd_aux, &verdaux)) + break; + + return elf_strptr(iter->elf, iter->verdef_strtabidx, verdaux.vda_name); + + } + return NULL; +} + +static bool symbol_match(struct elf_sym_iter *iter, int sh_type, struct elf_sym *sym, + const char *name, size_t name_len, const char *lib_ver) +{ + const char *ver_name; + + /* Symbols are in forms of func, func@LIB_VER or func@@LIB_VER + * make sure the func part matches the user specified name + */ + if (strncmp(sym->name, name, name_len) != 0) + return false; + + /* ...but we don't want a search for "foo" to match 'foo2" also, so any + * additional characters in sname should be of the form "@@LIB". + */ + if (sym->name[name_len] != '\0' && sym->name[name_len] != '@') + return false; + + /* If user does not specify symbol version, then we got a match */ + if (!lib_ver) + return true; + + /* If user specifies symbol version, for dynamic symbols, + * get version name from ELF verdef section for comparison. + */ + if (sh_type == SHT_DYNSYM) { + ver_name = elf_get_vername(iter, sym->ver); + if (!ver_name) + return false; + return strcmp(ver_name, lib_ver) == 0; + } + + /* For normal symbols, it is already in form of func@LIB_VER */ + return strcmp(sym->name, name) == 0; +} /* Transform symbol's virtual address (absolute for binaries and relative * for shared libs) into file offset, which is what kernel is expecting @@ -166,7 +274,8 @@ static unsigned long elf_sym_offset(struct elf_sym *sym) long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name) { int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB }; - bool is_shared_lib, is_name_qualified; + const char *at_symbol, *lib_ver; + bool is_shared_lib; long ret = -ENOENT; size_t name_len; GElf_Ehdr ehdr; @@ -179,9 +288,18 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name) /* for shared lib case, we do not need to calculate relative offset */ is_shared_lib = ehdr.e_type == ET_DYN; - name_len = strlen(name); - /* Does name specify "@@LIB"? */ - is_name_qualified = strstr(name, "@@") != NULL; + /* Does name specify "@@LIB_VER" or "@LIB_VER" ? */ + at_symbol = strchr(name, '@'); + if (at_symbol) { + name_len = at_symbol - name; + /* skip second @ if it's @@LIB_VER case */ + if (at_symbol[1] == '@') + at_symbol++; + lib_ver = at_symbol + 1; + } else { + name_len = strlen(name); + lib_ver = NULL; + } /* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if * a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically @@ -201,13 +319,7 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name) goto out; while ((sym = elf_sym_iter_next(&iter))) { - /* User can specify func, func@@LIB or func@@LIB_VERSION. */ - if (strncmp(sym->name, name, name_len) != 0) - continue; - /* ...but we don't want a search for "foo" to match 'foo2" also, so any - * additional characters in sname should be of the form "@@LIB". - */ - if (!is_name_qualified && sym->name[name_len] != '\0' && sym->name[name_len] != '@') + if (!symbol_match(&iter, sh_types[i], sym, name, name_len, lib_ver)) continue; cur_bind = GELF_ST_BIND(sym->sym.st_info); diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 3a6108e3238b..b4758e54a815 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -11630,7 +11630,7 @@ static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf *link = NULL; - n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.]+%li", + n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.@]+%li", &probe_type, &binary_path, &func_name, &offset); switch (n) { case 1: -- 2.20.1