diff options
Diffstat (limited to 'tools/testing/selftests/vDSO')
| -rw-r--r-- | tools/testing/selftests/vDSO/.gitignore | 2 | ||||
| -rw-r--r-- | tools/testing/selftests/vDSO/Makefile | 20 | ||||
| -rw-r--r-- | tools/testing/selftests/vDSO/parse_vdso.c | 269 | ||||
| -rw-r--r-- | tools/testing/selftests/vDSO/vdso_standalone_test_x86.c | 128 | ||||
| -rw-r--r-- | tools/testing/selftests/vDSO/vdso_test.c | 52 |
5 files changed, 471 insertions, 0 deletions
diff --git a/tools/testing/selftests/vDSO/.gitignore b/tools/testing/selftests/vDSO/.gitignore new file mode 100644 index 000000000000..133bf9ee986c --- /dev/null +++ b/tools/testing/selftests/vDSO/.gitignore @@ -0,0 +1,2 @@ +vdso_test +vdso_standalone_test_x86 diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile new file mode 100644 index 000000000000..706b68b1c372 --- /dev/null +++ b/tools/testing/selftests/vDSO/Makefile @@ -0,0 +1,20 @@ +ifndef CROSS_COMPILE +CFLAGS := -std=gnu99 +CFLAGS_vdso_standalone_test_x86 := -nostdlib -fno-asynchronous-unwind-tables -fno-stack-protector +ifeq ($(CONFIG_X86_32),y) +LDLIBS += -lgcc_s +endif + +TEST_PROGS := vdso_test vdso_standalone_test_x86 + +all: $(TEST_PROGS) +vdso_test: parse_vdso.c vdso_test.c +vdso_standalone_test_x86: vdso_standalone_test_x86.c parse_vdso.c + $(CC) $(CFLAGS) $(CFLAGS_vdso_standalone_test_x86) \ + vdso_standalone_test_x86.c parse_vdso.c \ + -o vdso_standalone_test_x86 + +include ../lib.mk +clean: + rm -fr $(TEST_PROGS) +endif diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c new file mode 100644 index 000000000000..1dbb4b87268f --- /dev/null +++ b/tools/testing/selftests/vDSO/parse_vdso.c @@ -0,0 +1,269 @@ +/* + * parse_vdso.c: Linux reference vDSO parser + * Written by Andrew Lutomirski, 2011-2014. + * + * This code is meant to be linked in to various programs that run on Linux. + * As such, it is available with as few restrictions as possible. This file + * is licensed under the Creative Commons Zero License, version 1.0, + * available at http://creativecommons.org/publicdomain/zero/1.0/legalcode + * + * The vDSO is a regular ELF DSO that the kernel maps into user space when + * it starts a program. It works equally well in statically and dynamically + * linked binaries. + * + * This code is tested on x86. In principle it should work on any + * architecture that has a vDSO. + */ + +#include <stdbool.h> +#include <stdint.h> +#include <string.h> +#include <limits.h> +#include <elf.h> + +/* + * To use this vDSO parser, first call one of the vdso_init_* functions. + * If you've already parsed auxv, then pass the value of AT_SYSINFO_EHDR + * to vdso_init_from_sysinfo_ehdr. Otherwise pass auxv to vdso_init_from_auxv. + * Then call vdso_sym for each symbol you want. For example, to look up + * gettimeofday on x86_64, use: + * + * <some pointer> = vdso_sym("LINUX_2.6", "gettimeofday"); + * or + * <some pointer> = vdso_sym("LINUX_2.6", "__vdso_gettimeofday"); + * + * vdso_sym will return 0 if the symbol doesn't exist or if the init function + * failed or was not called. vdso_sym is a little slow, so its return value + * should be cached. + * + * vdso_sym is threadsafe; the init functions are not. + * + * These are the prototypes: + */ +extern void vdso_init_from_auxv(void *auxv); +extern void vdso_init_from_sysinfo_ehdr(uintptr_t base); +extern void *vdso_sym(const char *version, const char *name); + + +/* And here's the code. */ +#ifndef ELF_BITS +# if ULONG_MAX > 0xffffffffUL +# define ELF_BITS 64 +# else +# define ELF_BITS 32 +# endif +#endif + +#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x +#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x) +#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x) + +static struct vdso_info +{ + bool valid; + + /* Load information */ + uintptr_t load_addr; + uintptr_t load_offset; /* load_addr - recorded vaddr */ + + /* Symbol table */ + ELF(Sym) *symtab; + const char *symstrings; + ELF(Word) *bucket, *chain; + ELF(Word) nbucket, nchain; + + /* Version table */ + ELF(Versym) *versym; + ELF(Verdef) *verdef; +} vdso_info; + +/* Straight from the ELF specification. */ +static unsigned long elf_hash(const unsigned char *name) +{ + unsigned long h = 0, g; + while (*name) + { + h = (h << 4) + *name++; + if (g = h & 0xf0000000) + h ^= g >> 24; + h &= ~g; + } + return h; +} + +void vdso_init_from_sysinfo_ehdr(uintptr_t base) +{ + size_t i; + bool found_vaddr = false; + + vdso_info.valid = false; + + vdso_info.load_addr = base; + + ELF(Ehdr) *hdr = (ELF(Ehdr)*)base; + if (hdr->e_ident[EI_CLASS] != + (ELF_BITS == 32 ? ELFCLASS32 : ELFCLASS64)) { + return; /* Wrong ELF class -- check ELF_BITS */ + } + + ELF(Phdr) *pt = (ELF(Phdr)*)(vdso_info.load_addr + hdr->e_phoff); + ELF(Dyn) *dyn = 0; + + /* + * We need two things from the segment table: the load offset + * and the dynamic table. + */ + for (i = 0; i < hdr->e_phnum; i++) + { + if (pt[i].p_type == PT_LOAD && !found_vaddr) { + found_vaddr = true; + vdso_info.load_offset = base + + (uintptr_t)pt[i].p_offset + - (uintptr_t)pt[i].p_vaddr; + } else if (pt[i].p_type == PT_DYNAMIC) { + dyn = (ELF(Dyn)*)(base + pt[i].p_offset); + } + } + + if (!found_vaddr || !dyn) + return; /* Failed */ + + /* + * Fish out the useful bits of the dynamic table. + */ + ELF(Word) *hash = 0; + vdso_info.symstrings = 0; + vdso_info.symtab = 0; + vdso_info.versym = 0; + vdso_info.verdef = 0; + for (i = 0; dyn[i].d_tag != DT_NULL; i++) { + switch (dyn[i].d_tag) { + case DT_STRTAB: + vdso_info.symstrings = (const char *) + ((uintptr_t)dyn[i].d_un.d_ptr + + vdso_info.load_offset); + break; + case DT_SYMTAB: + vdso_info.symtab = (ELF(Sym) *) + ((uintptr_t)dyn[i].d_un.d_ptr + + vdso_info.load_offset); + break; + case DT_HASH: + hash = (ELF(Word) *) + ((uintptr_t)dyn[i].d_un.d_ptr + + vdso_info.load_offset); + break; + case DT_VERSYM: + vdso_info.versym = (ELF(Versym) *) + ((uintptr_t)dyn[i].d_un.d_ptr + + vdso_info.load_offset); + break; + case DT_VERDEF: + vdso_info.verdef = (ELF(Verdef) *) + ((uintptr_t)dyn[i].d_un.d_ptr + + vdso_info.load_offset); + break; + } + } + if (!vdso_info.symstrings || !vdso_info.symtab || !hash) + return; /* Failed */ + + if (!vdso_info.verdef) + vdso_info.versym = 0; + + /* Parse the hash table header. */ + vdso_info.nbucket = hash[0]; + vdso_info.nchain = hash[1]; + vdso_info.bucket = &hash[2]; + vdso_info.chain = &hash[vdso_info.nbucket + 2]; + + /* That's all we need. */ + vdso_info.valid = true; +} + +static bool vdso_match_version(ELF(Versym) ver, + const char *name, ELF(Word) hash) +{ + /* + * This is a helper function to check if the version indexed by + * ver matches name (which hashes to hash). + * + * The version definition table is a mess, and I don't know how + * to do this in better than linear time without allocating memory + * to build an index. I also don't know why the table has + * variable size entries in the first place. + * + * For added fun, I can't find a comprehensible specification of how + * to parse all the weird flags in the table. + * + * So I just parse the whole table every time. + */ + + /* First step: find the version definition */ + ver &= 0x7fff; /* Apparently bit 15 means "hidden" */ + ELF(Verdef) *def = vdso_info.verdef; + while(true) { + if ((def->vd_flags & VER_FLG_BASE) == 0 + && (def->vd_ndx & 0x7fff) == ver) + break; + + if (def->vd_next == 0) + return false; /* No definition. */ + + def = (ELF(Verdef) *)((char *)def + def->vd_next); + } + + /* Now figure out whether it matches. */ + ELF(Verdaux) *aux = (ELF(Verdaux)*)((char *)def + def->vd_aux); + return def->vd_hash == hash + && !strcmp(name, vdso_info.symstrings + aux->vda_name); +} + +void *vdso_sym(const char *version, const char *name) +{ + unsigned long ver_hash; + if (!vdso_info.valid) + return 0; + + ver_hash = elf_hash(version); + ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket]; + + for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) { + ELF(Sym) *sym = &vdso_info.symtab[chain]; + + /* Check for a defined global or weak function w/ right name. */ + if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC) + continue; + if (ELF64_ST_BIND(sym->st_info) != STB_GLOBAL && + ELF64_ST_BIND(sym->st_info) != STB_WEAK) + continue; + if (sym->st_shndx == SHN_UNDEF) + continue; + if (strcmp(name, vdso_info.symstrings + sym->st_name)) + continue; + + /* Check symbol version. */ + if (vdso_info.versym + && !vdso_match_version(vdso_info.versym[chain], + version, ver_hash)) + continue; + + return (void *)(vdso_info.load_offset + sym->st_value); + } + + return 0; +} + +void vdso_init_from_auxv(void *auxv) +{ + ELF(auxv_t) *elf_auxv = auxv; + for (int i = 0; elf_auxv[i].a_type != AT_NULL; i++) + { + if (elf_auxv[i].a_type == AT_SYSINFO_EHDR) { + vdso_init_from_sysinfo_ehdr(elf_auxv[i].a_un.a_val); + return; + } + } + + vdso_info.valid = false; +} diff --git a/tools/testing/selftests/vDSO/vdso_standalone_test_x86.c b/tools/testing/selftests/vDSO/vdso_standalone_test_x86.c new file mode 100644 index 000000000000..93b0ebf8cc38 --- /dev/null +++ b/tools/testing/selftests/vDSO/vdso_standalone_test_x86.c @@ -0,0 +1,128 @@ +/* + * vdso_test.c: Sample code to test parse_vdso.c on x86 + * Copyright (c) 2011-2014 Andy Lutomirski + * Subject to the GNU General Public License, version 2 + * + * You can amuse yourself by compiling with: + * gcc -std=gnu99 -nostdlib + * -Os -fno-asynchronous-unwind-tables -flto -lgcc_s + * vdso_standalone_test_x86.c parse_vdso.c + * to generate a small binary. On x86_64, you can omit -lgcc_s + * if you want the binary to be completely standalone. + */ + +#include <sys/syscall.h> +#include <sys/time.h> +#include <unistd.h> +#include <stdint.h> + +extern void *vdso_sym(const char *version, const char *name); +extern void vdso_init_from_sysinfo_ehdr(uintptr_t base); +extern void vdso_init_from_auxv(void *auxv); + +/* We need a libc functions... */ +int strcmp(const char *a, const char *b) +{ + /* This implementation is buggy: it never returns -1. */ + while (*a || *b) { + if (*a != *b) + return 1; + if (*a == 0 || *b == 0) + return 1; + a++; + b++; + } + + return 0; +} + +/* ...and two syscalls. This is x86-specific. */ +static inline long x86_syscall3(long nr, long a0, long a1, long a2) +{ + long ret; +#ifdef __x86_64__ + asm volatile ("syscall" : "=a" (ret) : "a" (nr), + "D" (a0), "S" (a1), "d" (a2) : + "cc", "memory", "rcx", + "r8", "r9", "r10", "r11" ); +#else + asm volatile ("int $0x80" : "=a" (ret) : "a" (nr), + "b" (a0), "c" (a1), "d" (a2) : + "cc", "memory" ); +#endif + return ret; +} + +static inline long linux_write(int fd, const void *data, size_t len) +{ + return x86_syscall3(__NR_write, fd, (long)data, (long)len); +} + +static inline void linux_exit(int code) +{ + x86_syscall3(__NR_exit, code, 0, 0); +} + +void to_base10(char *lastdig, time_t n) +{ + while (n) { + *lastdig = (n % 10) + '0'; + n /= 10; + lastdig--; + } +} + +__attribute__((externally_visible)) void c_main(void **stack) +{ + /* Parse the stack */ + long argc = (long)*stack; + stack += argc + 2; + + /* Now we're pointing at the environment. Skip it. */ + while(*stack) + stack++; + stack++; + + /* Now we're pointing at auxv. Initialize the vDSO parser. */ + vdso_init_from_auxv((void *)stack); + + /* Find gettimeofday. */ + typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz); + gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday"); + + if (!gtod) + linux_exit(1); + + struct timeval tv; + long ret = gtod(&tv, 0); + + if (ret == 0) { + char buf[] = "The time is .000000\n"; + to_base10(buf + 31, tv.tv_sec); + to_base10(buf + 38, tv.tv_usec); + linux_write(1, buf, sizeof(buf) - 1); + } else { + linux_exit(ret); + } + + linux_exit(0); +} + +/* + * This is the real entry point. It passes the initial stack into + * the C entry point. + */ +asm ( + ".text\n" + ".global _start\n" + ".type _start,@function\n" + "_start:\n\t" +#ifdef __x86_64__ + "mov %rsp,%rdi\n\t" + "jmp c_main" +#else + "push %esp\n\t" + "call c_main\n\t" + "int $3" +#endif + ); diff --git a/tools/testing/selftests/vDSO/vdso_test.c b/tools/testing/selftests/vDSO/vdso_test.c new file mode 100644 index 000000000000..8daeb7d7032c --- /dev/null +++ b/tools/testing/selftests/vDSO/vdso_test.c @@ -0,0 +1,52 @@ +/* + * vdso_test.c: Sample code to test parse_vdso.c + * Copyright (c) 2014 Andy Lutomirski + * Subject to the GNU General Public License, version 2 + * + * Compile with: + * gcc -std=gnu99 vdso_test.c parse_vdso.c + * + * Tested on x86, 32-bit and 64-bit. It may work on other architectures, too. + */ + +#include <stdint.h> +#include <elf.h> +#include <stdio.h> +#include <sys/auxv.h> +#include <sys/time.h> + +extern void *vdso_sym(const char *version, const char *name); +extern void vdso_init_from_sysinfo_ehdr(uintptr_t base); +extern void vdso_init_from_auxv(void *auxv); + +int main(int argc, char **argv) +{ + unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR); + if (!sysinfo_ehdr) { + printf("AT_SYSINFO_EHDR is not present!\n"); + return 0; + } + + vdso_init_from_sysinfo_ehdr(getauxval(AT_SYSINFO_EHDR)); + + /* Find gettimeofday. */ + typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz); + gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday"); + + if (!gtod) { + printf("Could not find __vdso_gettimeofday\n"); + return 1; + } + + struct timeval tv; + long ret = gtod(&tv, 0); + + if (ret == 0) { + printf("The time is %lld.%06lld\n", + (long long)tv.tv_sec, (long long)tv.tv_usec); + } else { + printf("__vdso_gettimeofday failed\n"); + } + + return 0; +} |