Extend elf-parse to be able to read the symbol table of vmlinux in kallsyms.
This requires the ability to open ELF files in read-only mode, so provide elf_map_ro() to do so. It also requires accessors for section flags and symbol bindings, so provide these via shdr_flags() and sym_bind(). It's useful to be able to open an ELF file, map it, and then have easy access to its section headers, names and symbol table, so introduce struct elf_file to store this. In order to obtain this data also provide elf_open_ro() and elf_close(). Also, check for the file being an ELF file first in elf_parse(). This is the logical thing to check for first, but additionally prevents kallsyms from having to check this it self. Assisted-by: LLM Reviewed-by: Kees Cook <[email protected]> Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]> --- scripts/elf-parse.c | 103 +++++++++++++++++++++++++++++++++++++++++++++------- scripts/elf-parse.h | 54 +++++++++++++++++++++++++++ 2 files changed, 144 insertions(+), 13 deletions(-) diff --git a/scripts/elf-parse.c b/scripts/elf-parse.c index 99869ff91a8c..ce1c2a670244 100644 --- a/scripts/elf-parse.c +++ b/scripts/elf-parse.c @@ -17,15 +17,21 @@ struct elf_funcs elf_parser; * Get the whole file as a programming convenience in order to avoid * malloc+lseek+read+free of many pieces. If successful, then mmap * avoids copying unused pieces; else just read the whole file. - * Open for both read and write. + * Open for both read and write if writable is true, otherwise open + * read-only. */ -static void *map_file(char const *fname, size_t *size) +static void *map_file(char const *fname, size_t *size, bool writable) { - int fd; + int fd, prot = PROT_READ, flags = MAP_PRIVATE; struct stat sb; void *addr = NULL; - fd = open(fname, O_RDWR); + if (writable) { + prot |= PROT_WRITE; + flags = MAP_SHARED; + } + + fd = open(fname, writable ? O_RDWR : O_RDONLY); if (fd < 0) { perror(fname); return NULL; @@ -39,7 +45,7 @@ static void *map_file(char const *fname, size_t *size) goto out; } - addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); + addr = mmap(0, sb.st_size, prot, flags, fd, 0); if (addr == MAP_FAILED) { fprintf(stderr, "Could not mmap file: %s\n", fname); goto out; @@ -57,6 +63,12 @@ static int elf_parse(const char *fname, void *addr, uint32_t types) Elf_Ehdr *ehdr = addr; uint16_t type; + if (memcmp(ELFMAG, ehdr->e32.e_ident, SELFMAG) != 0 || + ehdr->e32.e_ident[EI_VERSION] != EV_CURRENT) { + fprintf(stderr, "unrecognized ELF file %s\n", fname); + return -1; + } + switch (ehdr->e32.e_ident[EI_DATA]) { case ELFDATA2LSB: elf_parser.r = rle; @@ -78,12 +90,6 @@ static int elf_parse(const char *fname, void *addr, uint32_t types) return -1; } - if (memcmp(ELFMAG, ehdr->e32.e_ident, SELFMAG) != 0 || - ehdr->e32.e_ident[EI_VERSION] != EV_CURRENT) { - fprintf(stderr, "unrecognized ELF file %s\n", fname); - return -1; - } - type = elf_parser.r2(&ehdr->e32.e_type); if (!((1 << type) & types)) { fprintf(stderr, "Invalid ELF type file %s\n", fname); @@ -103,7 +109,9 @@ static int elf_parse(const char *fname, void *addr, uint32_t types) elf_parser.shdr_name = shdr32_name; elf_parser.shdr_type = shdr32_type; elf_parser.shdr_entsize = shdr32_entsize; + elf_parser.shdr_flags = shdr32_flags; elf_parser.sym_type = sym32_type; + elf_parser.sym_bind = sym32_bind; elf_parser.sym_name = sym32_name; elf_parser.sym_value = sym32_value; elf_parser.sym_shndx = sym32_shndx; @@ -133,7 +141,9 @@ static int elf_parse(const char *fname, void *addr, uint32_t types) elf_parser.shdr_name = shdr64_name; elf_parser.shdr_type = shdr64_type; elf_parser.shdr_entsize = shdr64_entsize; + elf_parser.shdr_flags = shdr64_flags; elf_parser.sym_type = sym64_type; + elf_parser.sym_bind = sym64_bind; elf_parser.sym_name = sym64_name; elf_parser.sym_value = sym64_value; elf_parser.sym_shndx = sym64_shndx; @@ -174,12 +184,13 @@ int elf_map_long_size(void *addr) return ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32 ? 4 : 8; } -void *elf_map(char const *fname, size_t *size, uint32_t types) +static void *__elf_map(char const *fname, size_t *size, uint32_t types, + bool writable) { void *addr; int ret; - addr = map_file(fname, size); + addr = map_file(fname, size, writable); if (!addr) return NULL; @@ -192,7 +203,73 @@ void *elf_map(char const *fname, size_t *size, uint32_t types) return addr; } +void *elf_map(char const *fname, size_t *size, uint32_t types) +{ + return __elf_map(fname, size, types, true); +} + +/* For tools that only read the file. */ +void *elf_map_ro(char const *fname, size_t *size, uint32_t types) +{ + return __elf_map(fname, size, types, false); +} + void elf_unmap(void *addr, size_t size) { munmap(addr, size); } + +/* + * Open an ELF file and map it read-only, locating its section headers, section + * names and symbol table which are populated in the elf out parameter. + * + * Returns 0 on success, otherwise -1. + */ +int elf_open_ro(char const *fname, uint32_t types, struct elf_file *elf) +{ + Elf_Ehdr *ehdr; + Elf_Shdr *first; + unsigned int shstrndx, i; + + memset(elf, 0, sizeof(*elf)); + elf->base = elf_map_ro(fname, &elf->size, types); + if (!elf->base) + return -1; + + ehdr = elf->base; + elf->shdrs = (const char *)elf->base + ehdr_shoff(ehdr); + elf->shentsize = ehdr_shentsize(ehdr); + first = elf_section(elf, 0); + + /* A count or index too large for the header lives in section 0. */ + elf->shnum = ehdr_shnum(ehdr); + if (elf->shnum == SHN_UNDEF) + elf->shnum = shdr_size(first); + shstrndx = ehdr_shstrndx(ehdr); + if (shstrndx == SHN_XINDEX) + shstrndx = shdr_link(first); + elf->shstrtab = (const char *)elf->base + + shdr_offset(elf_section(elf, shstrndx)); + + for (i = 0; i < elf->shnum && !elf->symtab; i++) + if (shdr_type(elf_section(elf, i)) == SHT_SYMTAB) + elf->symtab = elf_section(elf, i); + + if (!elf->symtab) { + fprintf(stderr, "%s: no symbol table\n", fname); + elf_close(elf); + return -1; + } + + elf->strtab = (const char *)elf->base + + shdr_offset(elf_section(elf, shdr_link(elf->symtab))); + elf->nr_syms = shdr_size(elf->symtab) / shdr_entsize(elf->symtab); + + return 0; +} + +void elf_close(struct elf_file *elf) +{ + elf_unmap(elf->base, elf->size); + elf->base = NULL; +} diff --git a/scripts/elf-parse.h b/scripts/elf-parse.h index f4411e03069d..c5ad754da254 100644 --- a/scripts/elf-parse.h +++ b/scripts/elf-parse.h @@ -37,10 +37,12 @@ struct elf_funcs { uint64_t (*shdr_offset)(Elf_Shdr *shdr); uint64_t (*shdr_size)(Elf_Shdr *shdr); uint64_t (*shdr_entsize)(Elf_Shdr *shdr); + uint64_t (*shdr_flags)(Elf_Shdr *shdr); uint32_t (*shdr_link)(Elf_Shdr *shdr); uint32_t (*shdr_name)(Elf_Shdr *shdr); uint32_t (*shdr_type)(Elf_Shdr *shdr); uint8_t (*sym_type)(Elf_Sym *sym); + uint8_t (*sym_bind)(Elf_Sym *sym); uint32_t (*sym_name)(Elf_Sym *sym); uint64_t (*sym_value)(Elf_Sym *sym); uint16_t (*sym_shndx)(Elf_Sym *sym); @@ -143,6 +145,7 @@ SHDR_ADDR(addr) SHDR_ADDR(offset) SHDR_ADDR(size) SHDR_ADDR(entsize) +SHDR_ADDR(flags) SHDR_WORD(link) SHDR_WORD(name) @@ -211,6 +214,21 @@ static inline uint8_t sym_type(Elf_Sym *sym) return elf_parser.sym_type(sym); } +static inline uint8_t sym64_bind(Elf_Sym *sym) +{ + return ELF64_ST_BIND(sym->e64.st_info); +} + +static inline uint8_t sym32_bind(Elf_Sym *sym) +{ + return ELF32_ST_BIND(sym->e32.st_info); +} + +static inline uint8_t sym_bind(Elf_Sym *sym) +{ + return elf_parser.sym_bind(sym); +} + SYM_ADDR(value) SYM_WORD(name) SYM_HALF(shndx) @@ -298,8 +316,44 @@ static inline void w8le(uint64_t val, uint64_t *x) } void *elf_map(char const *fname, size_t *size, uint32_t types); +void *elf_map_ro(char const *fname, size_t *size, uint32_t types); void elf_unmap(void *addr, size_t size); int elf_map_machine(void *addr); int elf_map_long_size(void *addr); +/* A mapped file with its section headers, section names and symbol table. */ +struct elf_file { + void *base; + size_t size; + const char *shdrs; + unsigned int shnum, shentsize; + const char *shstrtab; + Elf_Shdr *symtab; + const char *strtab; + size_t nr_syms; +}; + +int elf_open_ro(char const *fname, uint32_t types, struct elf_file *elf); +void elf_close(struct elf_file *elf); + +static inline Elf_Shdr *elf_section(const struct elf_file *elf, + unsigned int index) +{ + return (Elf_Shdr *)(elf->shdrs + (size_t)index * elf->shentsize); +} + +static inline const char *elf_section_name(const struct elf_file *elf, + Elf_Shdr *shdr) +{ + return elf->shstrtab + shdr_name(shdr); +} + +static inline Elf_Sym *elf_symbol(const struct elf_file *elf, size_t index) +{ + const char *base = elf->base; + + return (Elf_Sym *)(base + shdr_offset(elf->symtab) + + index * shdr_entsize(elf->symtab)); +} + #endif /* _SCRIPTS_ELF_PARSE_H */ -- 2.55.0
