/*
* parse_vdso.c: Linux reference vDSO parser
- * Written by Andrew Lutomirski, 2011.
+ * 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
* it starts a program. It works equally well in statically and dynamically
* linked binaries.
*
- * This code is tested on x86_64. In principle it should work on any 64-bit
+ * 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>
/*
/* And here's the code. */
-
-#ifndef __x86_64__
-# error Not yet ported to non-x86_64 architectures
+#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;
uintptr_t load_offset; /* load_addr - recorded vaddr */
/* Symbol table */
- Elf64_Sym *symtab;
+ ELF(Sym) *symtab;
const char *symstrings;
- Elf64_Word *bucket, *chain;
- Elf64_Word nbucket, nchain;
+ ELF(Word) *bucket, *chain;
+ ELF(Word) nbucket, nchain;
/* Version table */
- Elf64_Versym *versym;
- Elf64_Verdef *verdef;
+ ELF(Versym) *versym;
+ ELF(Verdef) *verdef;
} vdso_info;
/* Straight from the ELF specification. */
vdso_info.load_addr = base;
- Elf64_Ehdr *hdr = (Elf64_Ehdr*)base;
- Elf64_Phdr *pt = (Elf64_Phdr*)(vdso_info.load_addr + hdr->e_phoff);
- Elf64_Dyn *dyn = 0;
+ 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
+ (uintptr_t)pt[i].p_offset
- (uintptr_t)pt[i].p_vaddr;
} else if (pt[i].p_type == PT_DYNAMIC) {
- dyn = (Elf64_Dyn*)(base + pt[i].p_offset);
+ dyn = (ELF(Dyn)*)(base + pt[i].p_offset);
}
}
/*
* Fish out the useful bits of the dynamic table.
*/
- Elf64_Word *hash = 0;
+ ELF(Word) *hash = 0;
vdso_info.symstrings = 0;
vdso_info.symtab = 0;
vdso_info.versym = 0;
+ vdso_info.load_offset);
break;
case DT_SYMTAB:
- vdso_info.symtab = (Elf64_Sym *)
+ vdso_info.symtab = (ELF(Sym) *)
((uintptr_t)dyn[i].d_un.d_ptr
+ vdso_info.load_offset);
break;
case DT_HASH:
- hash = (Elf64_Word *)
+ hash = (ELF(Word) *)
((uintptr_t)dyn[i].d_un.d_ptr
+ vdso_info.load_offset);
break;
case DT_VERSYM:
- vdso_info.versym = (Elf64_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 = (Elf64_Verdef *)
+ vdso_info.verdef = (ELF(Verdef) *)
((uintptr_t)dyn[i].d_un.d_ptr
+ vdso_info.load_offset);
break;
vdso_info.valid = true;
}
-static bool vdso_match_version(Elf64_Versym ver,
- const char *name, Elf64_Word hash)
+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
/* First step: find the version definition */
ver &= 0x7fff; /* Apparently bit 15 means "hidden" */
- Elf64_Verdef *def = vdso_info.verdef;
+ ELF(Verdef) *def = vdso_info.verdef;
while(true) {
if ((def->vd_flags & VER_FLG_BASE) == 0
&& (def->vd_ndx & 0x7fff) == ver)
if (def->vd_next == 0)
return false; /* No definition. */
- def = (Elf64_Verdef *)((char *)def + def->vd_next);
+ def = (ELF(Verdef) *)((char *)def + def->vd_next);
}
/* Now figure out whether it matches. */
- Elf64_Verdaux *aux = (Elf64_Verdaux*)((char *)def + def->vd_aux);
+ ELF(Verdaux) *aux = (ELF(Verdaux)*)((char *)def + def->vd_aux);
return def->vd_hash == hash
&& !strcmp(name, vdso_info.symstrings + aux->vda_name);
}
return 0;
ver_hash = elf_hash(version);
- Elf64_Word chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
+ ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
- Elf64_Sym *sym = &vdso_info.symtab[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)
void vdso_init_from_auxv(void *auxv)
{
- Elf64_auxv_t *elf_auxv = 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) {
--- /dev/null
+/*
+ * 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, uint64_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
+ );
/*
- * vdso_test.c: Sample code to test parse_vdso.c on x86_64
- * Copyright (c) 2011 Andy Lutomirski
+ * vdso_test.c: Sample code to test parse_vdso.c
+ * Copyright (c) 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
- * vdso_test.c parse_vdso.c -o vdso_test
- * to generate a small binary with no dependencies at all.
+ * 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 <sys/syscall.h>
-#include <sys/time.h>
-#include <unistd.h>
#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);
-/* We need a libc functions... */
-int strcmp(const char *a, const char *b)
+int main(int argc, char **argv)
{
- /* 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++;
+ unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR);
+ if (!sysinfo_ehdr) {
+ printf("AT_SYSINFO_EHDR is not present!\n");
+ return 0;
}
- return 0;
-}
-
-/* ...and two syscalls. This is x86_64-specific. */
-static inline long linux_write(int fd, const void *data, size_t len)
-{
-
- long ret;
- asm volatile ("syscall" : "=a" (ret) : "a" (__NR_write),
- "D" (fd), "S" (data), "d" (len) :
- "cc", "memory", "rcx",
- "r8", "r9", "r10", "r11" );
- return ret;
-}
-
-static inline void linux_exit(int code)
-{
- asm volatile ("syscall" : : "a" (__NR_exit), "D" (code));
-}
-
-void to_base10(char *lastdig, uint64_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);
+ 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)
- linux_exit(1);
+ if (!gtod) {
+ printf("Could not find __vdso_gettimeofday\n");
+ return 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);
+ printf("The time is %lld.%06lld\n",
+ (long long)tv.tv_sec, (long long)tv.tv_usec);
} else {
- linux_exit(ret);
+ printf("__vdso_gettimeofday failed\n");
}
- linux_exit(0);
+ return 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"
- "mov %rsp,%rdi\n\t"
- "jmp c_main"
- );
VDSO32-$(CONFIG_X86_32) := y
VDSO32-$(CONFIG_COMPAT) := y
-vdso-install-$(VDSO64-y) += vdso.so
-vdso-install-$(VDSOX32-y) += vdsox32.so
-vdso-install-$(VDSO32-y) += $(vdso32-images)
-
-
# files to link into the vdso
-vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o
-
-vobjs-$(VDSOX32-y) += $(vobjx32s-compat)
-
-# Filter out x32 objects.
-vobj64s := $(filter-out $(vobjx32s-compat),$(vobjs-y))
+vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o vdso-fakesections.o
+vobjs-nox32 := vdso-fakesections.o
# files to link into kernel
obj-y += vma.o
obj-$(VDSO32-y) += vdso32-setup.o
-vobjs := $(foreach F,$(vobj64s),$(obj)/$F)
+vobjs := $(foreach F,$(vobjs-y),$(obj)/$F)
$(obj)/vdso.o: $(obj)/vdso.so
-Wl,-z,max-page-size=4096 \
-Wl,-z,common-page-size=4096
-vobjx32s-y := $(vobj64s:.o=-x32.o)
+# 64-bit objects to re-brand as x32
+vobjs64-for-x32 := $(filter-out $(vobjs-nox32),$(vobjs-y))
+
+# x32-rebranded versions
+vobjx32s-y := $(vobjs64-for-x32:.o=-x32.o)
+
+# same thing, but in the output directory
vobjx32s := $(foreach F,$(vobjx32s-y),$(obj)/$F)
# Convert 64bit object file to x32 for x32 vDSO.
GCOV_PROFILE := n
#
-# Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
+# Install the unstripped copies of vdso*.so.
#
-quiet_cmd_vdso_install = INSTALL $@
- cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@
-$(vdso-install-y): %.so: $(obj)/%.so.dbg FORCE
+quiet_cmd_vdso_install = INSTALL $(@:install_%=%)
+ cmd_vdso_install = cp $< $(MODLIB)/vdso/$(@:install_%=%)
+
+vdso_img_insttargets := $(vdso_img_sodbg:%.dbg=install_%)
+
+$(MODLIB)/vdso: FORCE
@mkdir -p $(MODLIB)/vdso
+
+$(vdso_img_insttargets): install_%: $(obj)/%.dbg $(MODLIB)/vdso FORCE
$(call cmd,vdso_install)
-PHONY += vdso_install $(vdso-install-y)
-vdso_install: $(vdso-install-y)
+PHONY += vdso_install $(vdso_img_insttargets)
+vdso_install: $(vdso_img_insttargets) FORCE
clean-files := vdso32-syscall* vdso32-sysenter* vdso32-int80*
--- /dev/null
+/*
+ * Copyright 2014 Andy Lutomirski
+ * Subject to the GNU Public License, v.2
+ *
+ * Hack to keep broken Go programs working.
+ *
+ * The Go runtime had a couple of bugs: it would read the section table to try
+ * to figure out how many dynamic symbols there were (it shouldn't have looked
+ * at the section table at all) and, if there were no SHT_SYNDYM section table
+ * entry, it would use an uninitialized value for the number of symbols. As a
+ * workaround, we supply a minimal section table. vdso2c will adjust the
+ * in-memory image so that "vdso_fake_sections" becomes the section table.
+ *
+ * The bug was introduced by:
+ * https://code.google.com/p/go/source/detail?r=56ea40aac72b (2012-08-31)
+ * and is being addressed in the Go runtime in this issue:
+ * https://code.google.com/p/go/issues/detail?id=8197
+ */
+
+#ifndef __x86_64__
+#error This hack is specific to the 64-bit vDSO
+#endif
+
+#include <linux/elf.h>
+
+extern const __visible struct elf64_shdr vdso_fake_sections[];
+const __visible struct elf64_shdr vdso_fake_sections[] = {
+ {
+ .sh_type = SHT_DYNSYM,
+ .sh_entsize = sizeof(Elf64_Sym),
+ }
+};
}
/*
- * Evil macros to do a little-endian read.
+ * Evil macros for little-endian reads and writes
*/
#define GLE(x, bits, ifnot) \
__builtin_choose_expr( \
(__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)
extern void bad_get_le(void);
-#define LAST_LE(x) \
+#define LAST_GLE(x) \
__builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())
#define GET_LE(x) \
- GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_LE(x))))
+ GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))
+
+#define PLE(x, val, bits, ifnot) \
+ __builtin_choose_expr( \
+ (sizeof(*(x)) == bits/8), \
+ put_unaligned_le##bits((val), (x)), ifnot)
+
+extern void bad_put_le(void);
+#define LAST_PLE(x, val) \
+ __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())
+
+#define PUT_LE(x, val) \
+ PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
+
#define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))
const char *secstrings;
uint64_t syms[NSYMS] = {};
+ uint64_t fake_sections_value = 0, fake_sections_size = 0;
+
Elf_Phdr *pt = (Elf_Phdr *)(addr + GET_LE(&hdr->e_phoff));
/* Walk the segment table. */
GET_LE(&symtab_hdr->sh_entsize) * i;
const char *name = addr + GET_LE(&strtab_hdr->sh_offset) +
GET_LE(&sym->st_name);
+
for (k = 0; k < NSYMS; k++) {
if (!strcmp(name, required_syms[k])) {
if (syms[k]) {
syms[k] = GET_LE(&sym->st_value);
}
}
+
+ if (!strcmp(name, "vdso_fake_sections")) {
+ if (fake_sections_value)
+ fail("duplicate vdso_fake_sections\n");
+ fake_sections_value = GET_LE(&sym->st_value);
+ fake_sections_size = GET_LE(&sym->st_size);
+ }
}
/* Validate mapping addresses. */
if (syms[sym_end_mapping] % 4096)
fail("end_mapping must be a multiple of 4096\n");
- /* Remove sections. */
- hdr->e_shoff = 0;
- hdr->e_shentsize = 0;
- hdr->e_shnum = 0;
- hdr->e_shstrndx = htole16(SHN_UNDEF);
+ /* Remove sections or use fakes */
+ if (fake_sections_size % sizeof(Elf_Shdr))
+ fail("vdso_fake_sections size is not a multiple of %ld\n",
+ (long)sizeof(Elf_Shdr));
+ PUT_LE(&hdr->e_shoff, fake_sections_value);
+ PUT_LE(&hdr->e_shentsize, fake_sections_value ? sizeof(Elf_Shdr) : 0);
+ PUT_LE(&hdr->e_shnum, fake_sections_size / sizeof(Elf_Shdr));
+ PUT_LE(&hdr->e_shstrndx, SHN_UNDEF);
if (!name) {
fwrite(addr, load_size, 1, outfile);
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