Merge "make vdso function pointers read-only at runtime"
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commit
ca7bc509cf
@ -30,8 +30,14 @@
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#define VDSO_GETTIMEOFDAY_SYMBOL "__vdso_gettimeofday"
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#endif
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#include <errno.h>
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#include <limits.h>
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#include <sys/mman.h>
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#include <time.h>
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#include "private/bionic_prctl.h"
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#include "private/libc_logging.h"
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extern "C" int __clock_gettime(int, timespec*);
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extern "C" int __gettimeofday(timeval*, struct timezone*);
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@ -46,28 +52,33 @@ enum {
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VDSO_END
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};
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static vdso_entry vdso_entries[] = {
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static const vdso_entry vdso_entries_template[] = {
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[VDSO_CLOCK_GETTIME] = { VDSO_CLOCK_GETTIME_SYMBOL, reinterpret_cast<void*>(__clock_gettime) },
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[VDSO_GETTIMEOFDAY] = { VDSO_GETTIMEOFDAY_SYMBOL, reinterpret_cast<void*>(__gettimeofday) },
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};
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static vdso_entry* vdso_entries;
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int clock_gettime(int clock_id, timespec* tp) {
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static int (*vdso_clock_gettime)(int, timespec*) =
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int (*vdso_clock_gettime)(int, timespec*) =
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reinterpret_cast<int (*)(int, timespec*)>(vdso_entries[VDSO_CLOCK_GETTIME].fn);
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return vdso_clock_gettime(clock_id, tp);
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}
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int gettimeofday(timeval* tv, struct timezone* tz) {
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static int (*vdso_gettimeofday)(timeval*, struct timezone*) =
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int (*vdso_gettimeofday)(timeval*, struct timezone*) =
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reinterpret_cast<int (*)(timeval*, struct timezone*)>(vdso_entries[VDSO_GETTIMEOFDAY].fn);
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return vdso_gettimeofday(tv, tz);
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}
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void __libc_init_vdso() {
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static void __libc_init_vdso_entries() {
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// Set up the defaults in case we don't have a vdso or can't find everything we're looking for.
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memcpy(vdso_entries, vdso_entries_template, sizeof(vdso_entries_template));
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// Do we have a vdso?
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uintptr_t vdso_ehdr_addr = getauxval(AT_SYSINFO_EHDR);
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ElfW(Ehdr)* vdso_ehdr = reinterpret_cast<ElfW(Ehdr)*>(vdso_ehdr_addr);
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if (vdso_ehdr == NULL) {
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if (vdso_ehdr == nullptr) {
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return;
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}
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@ -85,7 +96,7 @@ void __libc_init_vdso() {
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// Where's the dynamic table?
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ElfW(Addr) vdso_addr = 0;
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ElfW(Dyn)* vdso_dyn = NULL;
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ElfW(Dyn)* vdso_dyn = nullptr;
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ElfW(Phdr)* vdso_phdr = reinterpret_cast<ElfW(Phdr)*>(vdso_ehdr_addr + vdso_ehdr->e_phoff);
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for (size_t i = 0; i < vdso_ehdr->e_phnum; ++i) {
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if (vdso_phdr[i].p_type == PT_DYNAMIC) {
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@ -94,13 +105,13 @@ void __libc_init_vdso() {
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vdso_addr = vdso_ehdr_addr + vdso_phdr[i].p_offset - vdso_phdr[i].p_vaddr;
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}
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}
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if (vdso_addr == 0 || vdso_dyn == NULL) {
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if (vdso_addr == 0 || vdso_dyn == nullptr) {
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return;
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}
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// Where are the string and symbol tables?
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const char* strtab = NULL;
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ElfW(Sym)* symtab = NULL;
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const char* strtab = nullptr;
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ElfW(Sym)* symtab = nullptr;
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for (ElfW(Dyn)* d = vdso_dyn; d->d_tag != DT_NULL; ++d) {
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if (d->d_tag == DT_STRTAB) {
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strtab = reinterpret_cast<const char*>(vdso_addr + d->d_un.d_ptr);
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@ -108,7 +119,7 @@ void __libc_init_vdso() {
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symtab = reinterpret_cast<ElfW(Sym)*>(vdso_addr + d->d_un.d_ptr);
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}
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}
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if (strtab == NULL || symtab == NULL) {
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if (strtab == nullptr || symtab == nullptr) {
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return;
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}
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@ -122,6 +133,20 @@ void __libc_init_vdso() {
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}
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}
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void __libc_init_vdso() {
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static_assert(PAGE_SIZE >= sizeof(vdso_entries_template), "vdso_entries_template too large");
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vdso_entries = reinterpret_cast<vdso_entry*>(mmap(nullptr, sizeof(vdso_entries_template), PROT_READ|PROT_WRITE,
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MAP_ANONYMOUS|MAP_PRIVATE, -1, 0));
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if (vdso_entries == MAP_FAILED) {
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__libc_fatal("failed to allocate vdso function pointer table: %s", strerror(errno));
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}
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__libc_init_vdso_entries();
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if (mprotect(vdso_entries, sizeof(vdso_entries_template), PROT_READ) == -1) {
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__libc_fatal("failed to mprotect PROT_READ vdso function pointer table: %s", strerror(errno));
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}
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prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, vdso_entries, sizeof(vdso_entries_template), "vdso function pointer table");
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}
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#else
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void __libc_init_vdso() {
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