Add regression coverage for libbpf static linker relocation offset checks. Build a minimal ET_REL/EM_BPF object in memory with a 16-byte executable section and one relocation against that section. Check that a valid relocation offset is accepted and an offset outside the relocated section is rejected with -EINVAL.
Assisted-by: Codex:gpt-5 Signed-off-by: HyeongJun An <[email protected]> --- .../selftests/bpf/prog_tests/libbpf_linker.c | 231 ++++++++++++++++++ 1 file changed, 231 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/libbpf_linker.c diff --git a/tools/testing/selftests/bpf/prog_tests/libbpf_linker.c b/tools/testing/selftests/bpf/prog_tests/libbpf_linker.c new file mode 100644 index 000000000000..a0a61b32fe2e --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/libbpf_linker.c @@ -0,0 +1,231 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <elf.h> +#include <errno.h> +#include <fcntl.h> +#include <unistd.h> + +#include <bpf/libbpf.h> +#include <linux/bpf.h> +#include <test_progs.h> + +#ifndef EM_BPF +#define EM_BPF 247 +#endif + +#ifndef R_BPF_64_64 +#define R_BPF_64_64 1 +#endif + +enum { + SEC_NULL, + SEC_TEXT, + SEC_REL_TEXT, + SEC_SYMTAB, + SEC_STRTAB, + SEC_SHSTRTAB, + SEC_CNT, +}; + +enum { + SHSTR_TEXT = 1, + SHSTR_REL_TEXT = SHSTR_TEXT + sizeof(".text"), + SHSTR_SYMTAB = SHSTR_REL_TEXT + sizeof(".rel.text"), + SHSTR_STRTAB = SHSTR_SYMTAB + sizeof(".symtab"), + SHSTR_SHSTRTAB = SHSTR_STRTAB + sizeof(".strtab"), +}; + +struct test_elf { + void *buf; + size_t sz; +}; + +static size_t elf_round_up(size_t value, size_t align) +{ + return (value + align - 1) / align * align; +} + +static unsigned char elf_byteorder(void) +{ +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ + return ELFDATA2LSB; +#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ + return ELFDATA2MSB; +#else +#error "Unrecognized __BYTE_ORDER__" +#endif +} + +/* + * Build a minimal ET_REL object in memory. A normal .bpf.c source cannot + * produce a relocation whose offset points past the relocated section, so the + * test constructs the ELF directly and feeds it to bpf_linker__add_buf(). + */ +static struct test_elf make_relo_obj(size_t relo_off) +{ + static const char shstrtab[] = "\0.text\0.rel.text\0.symtab\0.strtab\0.shstrtab"; + static const char strtab[] = "\0"; + struct bpf_insn insns[] = { + { + .code = BPF_ALU64 | BPF_MOV | BPF_K, + .dst_reg = BPF_REG_0, + .imm = 0, + }, + { + .code = BPF_JMP | BPF_EXIT, + }, + }; + size_t off, text_off, rel_off, symtab_off, strtab_off, shstrtab_off, shdr_off; + struct test_elf obj = {}; + Elf64_Shdr *shdr; + Elf64_Ehdr *ehdr; + Elf64_Sym *sym; + Elf64_Rel *rel; + + off = sizeof(*ehdr); + text_off = elf_round_up(off, 8); + off = text_off + sizeof(insns); + rel_off = elf_round_up(off, 8); + off = rel_off + sizeof(*rel); + symtab_off = elf_round_up(off, 8); + off = symtab_off + 2 * sizeof(*sym); + strtab_off = off; + off = strtab_off + sizeof(strtab); + shstrtab_off = off; + off = shstrtab_off + sizeof(shstrtab); + shdr_off = elf_round_up(off, 8); + off = shdr_off + SEC_CNT * sizeof(*shdr); + + obj.buf = calloc(1, off); + if (!obj.buf) + return obj; + obj.sz = off; + + ehdr = obj.buf; + memcpy(ehdr->e_ident, ELFMAG, SELFMAG); + ehdr->e_ident[EI_CLASS] = ELFCLASS64; + ehdr->e_ident[EI_DATA] = elf_byteorder(); + ehdr->e_ident[EI_VERSION] = EV_CURRENT; + ehdr->e_type = ET_REL; + ehdr->e_machine = EM_BPF; + ehdr->e_version = EV_CURRENT; + ehdr->e_ehsize = sizeof(*ehdr); + ehdr->e_shoff = shdr_off; + ehdr->e_shentsize = sizeof(*shdr); + ehdr->e_shnum = SEC_CNT; + ehdr->e_shstrndx = SEC_SHSTRTAB; + + memcpy(obj.buf + text_off, insns, sizeof(insns)); + + rel = obj.buf + rel_off; + rel->r_offset = relo_off; + rel->r_info = ELF64_R_INFO(1, R_BPF_64_64); + + sym = obj.buf + symtab_off; + sym[1].st_info = ELF64_ST_INFO(STB_LOCAL, STT_SECTION); + sym[1].st_shndx = SEC_TEXT; + + memcpy(obj.buf + strtab_off, strtab, sizeof(strtab)); + memcpy(obj.buf + shstrtab_off, shstrtab, sizeof(shstrtab)); + + shdr = obj.buf + shdr_off; + shdr[SEC_TEXT] = (Elf64_Shdr) { + .sh_name = SHSTR_TEXT, + .sh_type = SHT_PROGBITS, + .sh_flags = SHF_ALLOC | SHF_EXECINSTR, + .sh_offset = text_off, + .sh_size = sizeof(insns), + .sh_addralign = 8, + .sh_entsize = sizeof(struct bpf_insn), + }; + shdr[SEC_REL_TEXT] = (Elf64_Shdr) { + .sh_name = SHSTR_REL_TEXT, + .sh_type = SHT_REL, + .sh_offset = rel_off, + .sh_size = sizeof(*rel), + .sh_link = SEC_SYMTAB, + .sh_info = SEC_TEXT, + .sh_addralign = 8, + .sh_entsize = sizeof(*rel), + }; + shdr[SEC_SYMTAB] = (Elf64_Shdr) { + .sh_name = SHSTR_SYMTAB, + .sh_type = SHT_SYMTAB, + .sh_offset = symtab_off, + .sh_size = 2 * sizeof(*sym), + .sh_link = SEC_STRTAB, + .sh_info = 2, + .sh_addralign = 8, + .sh_entsize = sizeof(*sym), + }; + shdr[SEC_STRTAB] = (Elf64_Shdr) { + .sh_name = SHSTR_STRTAB, + .sh_type = SHT_STRTAB, + .sh_offset = strtab_off, + .sh_size = sizeof(strtab), + .sh_addralign = 1, + }; + shdr[SEC_SHSTRTAB] = (Elf64_Shdr) { + .sh_name = SHSTR_SHSTRTAB, + .sh_type = SHT_STRTAB, + .sh_offset = shstrtab_off, + .sh_size = sizeof(shstrtab), + .sh_addralign = 1, + }; + + return obj; +} + +static int link_relo_obj(size_t relo_off) +{ + char path[] = "/tmp/libbpf_linker_relo_XXXXXX"; + struct test_elf obj = {}; + struct bpf_linker *linker; + int err, fd; + + fd = mkstemp(path); + if (!ASSERT_OK_FD(fd, "mkstemp")) + return -errno; + close(fd); + + linker = bpf_linker__new(path, NULL); + if (!ASSERT_OK_PTR(linker, "linker_new")) { + err = libbpf_get_error(linker); + goto out_unlink; + } + + obj = make_relo_obj(relo_off); + if (!ASSERT_OK_PTR(obj.buf, "make_relo_obj")) { + err = -ENOMEM; + goto out_free_linker; + } + + err = bpf_linker__add_buf(linker, obj.buf, obj.sz, NULL); + if (!err) + err = bpf_linker__finalize(linker); + + free(obj.buf); +out_free_linker: + bpf_linker__free(linker); +out_unlink: + unlink(path); + return err; +} + +static void test_valid_relo_offset(void) +{ + ASSERT_OK(link_relo_obj(0), "valid_relo_offset"); +} + +static void test_invalid_relo_offset(void) +{ + ASSERT_EQ(link_relo_obj(0x1000), -EINVAL, "invalid_relo_offset"); +} + +void test_libbpf_linker(void) +{ + if (test__start_subtest("valid_relo_offset")) + test_valid_relo_offset(); + if (test__start_subtest("invalid_relo_offset")) + test_invalid_relo_offset(); +} -- 2.43.0
