Index: lib/cfi/cfi.cc =================================================================== --- lib/cfi/cfi.cc +++ lib/cfi/cfi.cc @@ -11,16 +11,11 @@ // //===----------------------------------------------------------------------===// -// FIXME: Intercept dlopen/dlclose. -// FIXME: Support diagnostic mode. -// FIXME: Harden: -// * mprotect shadow, use mremap for updates -// * something else equally important - #include #include #include #include +#include typedef ElfW(Phdr) Elf_Phdr; typedef ElfW(Ehdr) Elf_Ehdr; @@ -31,19 +26,31 @@ #include "ubsan/ubsan_init.h" #include "ubsan/ubsan_flags.h" -static uptr __cfi_shadow; +static constexpr uptr kCfiShadowPointerStorageSize = 4096; // 1 page +// Lets hope that the data segment is mapped with 4K pages. +// The pointer to the cfi shadow region is stored at the start of this page. +// The rest of the page is unused, re-mapped read-only and updated via mremap. +static char __cfi_shadow_pointer_storage[kCfiShadowPointerStorageSize] + __attribute__((aligned(kCfiShadowPointerStorageSize))); +static uptr __cfi_shadow_size; static constexpr uptr kShadowGranularity = 12; static constexpr uptr kShadowAlign = 1UL << kShadowGranularity; // 4096 static constexpr uint16_t kInvalidShadow = 0; static constexpr uint16_t kUncheckedShadow = 0xFFFFU; -static uint16_t *mem_to_shadow(uptr x) { - return (uint16_t *)(__cfi_shadow + ((x >> kShadowGranularity) << 1)); +// Get the start address of the CFI shadow region. +uptr GetShadow() { + return *reinterpret_cast(&__cfi_shadow_pointer_storage); +} + +static uint16_t *MemToShadow(uptr x, uptr shadow_base) { + return (uint16_t *)(shadow_base + ((x >> kShadowGranularity) << 1)); } typedef int (*CFICheckFn)(u64, void *, void *); +// This class reads and decodes the shadow contents. class ShadowValue { uptr addr; uint16_t v; @@ -63,40 +70,77 @@ // Load a shadow valud for the given application memory address. static const ShadowValue load(uptr addr) { - return ShadowValue(addr, *mem_to_shadow(addr)); + return ShadowValue(addr, *MemToShadow(addr, GetShadow())); } }; -static void fill_shadow_constant(uptr begin, uptr end, uint16_t v) { - assert(v == kInvalidShadow || v == kUncheckedShadow); - uint16_t *shadow_begin = mem_to_shadow(begin); - uint16_t *shadow_end = mem_to_shadow(end - 1) + 1; - memset(shadow_begin, v, (shadow_end - shadow_begin) * sizeof(*shadow_begin)); +class ShadowBuilder { + uptr shadow_; + +public: + // Allocate a new empty shadow (for the entire address space) on the side. + void Start(); + // Mark the given address range as unchecked. + // This is used for uninstrumented libraries like libc. + // Any CFI check with a target in that range will pass. + void AddUnchecked(uptr begin, uptr end); + // Mark the given address range as belonging to a library with the given + // cfi_check function. + void Add(uptr begin, uptr end, uptr cfi_check); + // Finish shadow construction. Atomically switch the current active shadow + // region with the newly constructed one and deallocate the former. + void Install(); +}; + +void ShadowBuilder::Start() { + shadow_ = (uptr)MmapNoReserveOrDie(__cfi_shadow_size, "CFI shadow"); + VReport(1, "CFI: shadow at %zx .. %zx\n", shadow_, + shadow_ + __cfi_shadow_size); } -static void fill_shadow(uptr begin, uptr end, uptr cfi_check) { +void ShadowBuilder::AddUnchecked(uptr begin, uptr end) { + uint16_t *shadow_begin = MemToShadow(begin, shadow_); + uint16_t *shadow_end = MemToShadow(end - 1, shadow_) + 1; + memset(shadow_begin, kUncheckedShadow, + (shadow_end - shadow_begin) * sizeof(*shadow_begin)); +} + +void ShadowBuilder::Add(uptr begin, uptr end, uptr cfi_check) { assert((cfi_check & (kShadowAlign - 1)) == 0); // Don't fill anything below cfi_check. We can not represent those addresses // in the shadow, and must make sure at codegen to place all valid call // targets above cfi_check. - uptr p = Max(begin, cfi_check); - uint16_t *s = mem_to_shadow(p); - uint16_t *s_end = mem_to_shadow(end - 1) + 1; - uint16_t sv = ((p - cfi_check) >> kShadowGranularity) + 1; + begin = Max(begin, cfi_check); + uint16_t *s = MemToShadow(begin, shadow_); + uint16_t *s_end = MemToShadow(end - 1, shadow_) + 1; + uint16_t sv = ((begin - cfi_check) >> kShadowGranularity) + 1; for (; s < s_end; s++, sv++) *s = sv; +} - // Sanity checks. - uptr q = p & ~(kShadowAlign - 1); - for (; q < end; q += kShadowAlign) { - assert((uptr)ShadowValue::load(q).get_cfi_check() == cfi_check); - assert((uptr)ShadowValue::load(q + kShadowAlign / 2).get_cfi_check() == - cfi_check); - assert((uptr)ShadowValue::load(q + kShadowAlign - 1).get_cfi_check() == - cfi_check); +#if SANITIZER_LINUX +void ShadowBuilder::Install() { + MprotectReadOnly(shadow_, __cfi_shadow_size); + uptr main_shadow = GetShadow(); + if (main_shadow) { + // Update. + void *res = mremap((void *)shadow_, __cfi_shadow_size, __cfi_shadow_size, + MREMAP_MAYMOVE | MREMAP_FIXED, main_shadow); + CHECK(res != MAP_FAILED); + } else { + // Initial setup. + CHECK_EQ(kCfiShadowPointerStorageSize, GetPageSizeCached()); + CHECK_EQ(0, GetShadow()); + *reinterpret_cast(&__cfi_shadow_pointer_storage) = shadow_; + MprotectReadOnly((uptr)&__cfi_shadow_pointer_storage, + kCfiShadowPointerStorageSize); + CHECK_EQ(shadow_, GetShadow()); } } +#else +#error not implemented +#endif // This is a workaround for a glibc bug: // https://sourceware.org/bugzilla/show_bug.cgi?id=15199 @@ -162,6 +206,8 @@ if (cfi_check) VReport(1, "Module '%s' __cfi_check %zx\n", info->dlpi_name, cfi_check); + ShadowBuilder *b = reinterpret_cast(data); + for (int i = 0; i < info->dlpi_phnum; i++) { const Elf_Phdr *phdr = &info->dlpi_phdr[i]; if (phdr->p_type == PT_LOAD) { @@ -174,18 +220,67 @@ uptr cur_end = cur_beg + phdr->p_memsz; if (cfi_check) { VReport(1, " %zx .. %zx\n", cur_beg, cur_end); - fill_shadow(cur_beg, cur_end, cfi_check ? cfi_check : (uptr)(-1)); + b->Add(cur_beg, cur_end, cfi_check); } else { - fill_shadow_constant(cur_beg, cur_end, kUncheckedShadow); + b->AddUnchecked(cur_beg, cur_end); } } } return 0; } -// Fill shadow for the initial libraries. -static void init_shadow() { - dl_iterate_phdr(dl_iterate_phdr_cb, nullptr); +// Init or update shadow for the current set of loaded libraries. +static void UpdateShadow() { + ShadowBuilder b; + b.Start(); + dl_iterate_phdr(dl_iterate_phdr_cb, &b); + b.Install(); +} + +static void InitShadow() { + // No difference, really. + UpdateShadow(); +} + +static THREADLOCAL int in_loader; +static BlockingMutex shadow_update_lock(LINKER_INITIALIZED); + +static void EnterLoader() { + if (in_loader == 0) { + shadow_update_lock.Lock(); + } + ++in_loader; +} + +static void ExitLoader() { + CHECK(in_loader > 0); + --in_loader; + UpdateShadow(); + if (in_loader == 0) { + shadow_update_lock.Unlock(); + } +} + +// Setup shadow for dlopen()ed libraries. +// The actual shadow setup happens after dlopen() returns, which means that +// a library can not be a target of any CFI checks while its constructors are +// running. It's unclear how to fix this without some extra help from libc. +// In glibc, mmap inside dlopen is not interceptable. +// Maybe a seccomp-bpf filter? +// We could insert a high-priority constructor into the library, but that would +// not help with the uninstrumented libraries. +INTERCEPTOR(void*, dlopen, const char *filename, int flag) { + EnterLoader(); + void *handle = REAL(dlopen)(filename, flag); + ExitLoader(); + return handle; +} + +INTERCEPTOR(int, dlclose, void *handle) { + EnterLoader(); + int res = REAL(dlclose)(handle); + ExitLoader(); + return res; } static ALWAYS_INLINE void CfiSlowPathCommon(u64 CallSiteTypeId, void *Ptr, @@ -201,7 +296,7 @@ if (DiagData) return; else - Die(); + Trap(); } if (sv.is_unchecked()) { VReport(2, "CFI: unchecked call (shadow=FFFF): %p\n", Ptr); @@ -263,13 +358,13 @@ uptr vma = GetMaxVirtualAddress(); // Shadow is 2 -> 2**kShadowGranularity. - uptr shadow_size = (vma >> (kShadowGranularity - 1)) + 1; - VReport(1, "CFI: VMA size %zx, shadow size %zx\n", vma, shadow_size); - void *shadow = MmapNoReserveOrDie(shadow_size, "CFI shadow"); - VReport(1, "CFI: shadow at %zx .. %zx\n", shadow, - reinterpret_cast(shadow) + shadow_size); - __cfi_shadow = (uptr)shadow; - init_shadow(); + __cfi_shadow_size = (vma >> (kShadowGranularity - 1)) + 1; + VReport(1, "CFI: VMA size %zx, shadow size %zx\n", vma, __cfi_shadow_size); + + InitShadow(); + + INTERCEPT_FUNCTION(dlopen); + INTERCEPT_FUNCTION(dlclose); #ifdef CFI_ENABLE_DIAG __ubsan::InitAsPlugin(); Index: lib/sanitizer_common/sanitizer_common.h =================================================================== --- lib/sanitizer_common/sanitizer_common.h +++ lib/sanitizer_common/sanitizer_common.h @@ -93,6 +93,7 @@ // Disallow access to a memory range. Use MmapNoAccess to allocate an // unaccessible memory. bool MprotectNoAccess(uptr addr, uptr size); +bool MprotectReadOnly(uptr addr, uptr size); // Used to check if we can map shadow memory to a fixed location. bool MemoryRangeIsAvailable(uptr range_start, uptr range_end); Index: lib/sanitizer_common/sanitizer_posix.cc =================================================================== --- lib/sanitizer_common/sanitizer_posix.cc +++ lib/sanitizer_common/sanitizer_posix.cc @@ -171,6 +171,10 @@ return 0 == internal_mprotect((void*)addr, size, PROT_NONE); } +bool MprotectReadOnly(uptr addr, uptr size) { + return 0 == internal_mprotect((void *)addr, size, PROT_READ); +} + fd_t OpenFile(const char *filename, FileAccessMode mode, error_t *errno_p) { int flags; switch (mode) { Index: test/cfi/cross-dso/dlopen.cpp =================================================================== --- /dev/null +++ test/cfi/cross-dso/dlopen.cpp @@ -0,0 +1,146 @@ +// RUN: %clangxx_cfi_dso -DSHARED_LIB %s -fPIC -shared -o %t1-so.so +// RUN: %clangxx_cfi_dso %s -o %t1 +// RUN: %expect_crash %t1 2>&1 | FileCheck --check-prefix=CFI %s +// RUN: %expect_crash %t1 cast 2>&1 | FileCheck --check-prefix=CFI-CAST %s +// RUN: %expect_crash %t1 dlclose 2>&1 | FileCheck --check-prefix=CFI %s + +// RUN: %clangxx_cfi_dso -DB32 -DSHARED_LIB %s -fPIC -shared -o %t2-so.so +// RUN: %clangxx_cfi_dso -DB32 %s -o %t2 +// RUN: %expect_crash %t2 2>&1 | FileCheck --check-prefix=CFI %s +// RUN: %expect_crash %t2 cast 2>&1 | FileCheck --check-prefix=CFI-CAST %s +// RUN: %expect_crash %t2 dlclose 2>&1 | FileCheck --check-prefix=CFI %s + +// RUN: %clangxx_cfi_dso -DB64 -DSHARED_LIB %s -fPIC -shared -o %t3-so.so +// RUN: %clangxx_cfi_dso -DB64 %s -o %t3 +// RUN: %expect_crash %t3 2>&1 | FileCheck --check-prefix=CFI %s +// RUN: %expect_crash %t3 cast 2>&1 | FileCheck --check-prefix=CFI-CAST %s +// RUN: %expect_crash %t3 dlclose 2>&1 | FileCheck --check-prefix=CFI %s + +// RUN: %clangxx_cfi_dso -DBM -DSHARED_LIB %s -fPIC -shared -o %t4-so.so +// RUN: %clangxx_cfi_dso -DBM %s -o %t4 +// RUN: %expect_crash %t4 2>&1 | FileCheck --check-prefix=CFI %s +// RUN: %expect_crash %t4 cast 2>&1 | FileCheck --check-prefix=CFI-CAST %s +// RUN: %expect_crash %t4 dlclose 2>&1 | FileCheck --check-prefix=CFI %s + +// RUN: %clangxx -g -DBM -DSHARED_LIB -DNOCFI %s -fPIC -shared -o %t5-so.so +// RUN: %clangxx -g -DBM -DNOCFI %s -ldl -o %t5 +// RUN: %t5 2>&1 | FileCheck --check-prefix=NCFI %s +// RUN: %t5 cast 2>&1 | FileCheck --check-prefix=NCFI %s +// RUN: %t5 dlclose 2>&1 | FileCheck --check-prefix=NCFI %s + +// Test that calls to uninstrumented library are unchecked. +// RUN: %clangxx -DBM -DSHARED_LIB %s -fPIC -shared -o %t6-so.so +// RUN: %clangxx_cfi_dso -DBM %s -o %t6 +// RUN: %t6 2>&1 | FileCheck --check-prefix=NCFI %s +// RUN: %t6 cast 2>&1 | FileCheck --check-prefix=NCFI %s + +// Call-after-dlclose is checked on the caller side. +// RUN: %expect_crash %t6 dlclose 2>&1 | FileCheck --check-prefix=CFI %s + +// Tests calls into dlopen-ed library. +// REQUIRES: cxxabi + +#include +#include +#include +#include +#include +#include + +struct A { + virtual void f(); +}; + +#ifdef SHARED_LIB + +#include "../utils.h" +struct B { + virtual void f(); +}; +void B::f() {} + +extern "C" void *create_B() { + create_derivers(); + return (void *)(new B()); +} + +extern "C" void do_nothing() __attribute__((aligned(4096))) {} + +#else + +void A::f() {} + +static const int kCodeAlign = 4096; +static const int kCodeSize = 4096; +static char saved_code[kCodeSize]; +static char *real_start; + +static void save_code(char *p) { + real_start = (char *)(((uintptr_t)p) & ~(kCodeAlign - 1)); + memcpy(saved_code, real_start, kCodeSize); +} + +static void restore_code() { + char *code = (char *)mmap(real_start, kCodeSize, PROT_WRITE | PROT_EXEC, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, 0, 0); + assert(code == real_start); + memcpy(code, saved_code, kCodeSize); +} + +int main(int argc, char *argv[]) { + const bool test_cast = argc > 1 && strcmp(argv[1], "cast") == 0; + const bool test_dlclose = argc > 1 && strcmp(argv[1], "dlclose") == 0; + + char name[100]; + snprintf(name, sizeof(name), "%s-so.so", argv[0]); + void *handle = dlopen(name, RTLD_NOW); + assert(handle); + void *(*create_B)() = (void *(*)())dlsym(handle, "create_B"); + assert(create_B); + + void *p = create_B(); + A *a; + + // CFI: =0= + // CFI-CAST: =0= + // NCFI: =0= + fprintf(stderr, "=0=\n"); + + if (test_cast) { + // Test cast. BOOM. + a = (A*)p; + } else { + // Invisible to CFI. Test virtual call later. + memcpy(&a, &p, sizeof(a)); + } + + // CFI: =1= + // CFI-CAST-NOT: =1= + // NCFI: =1= + fprintf(stderr, "=1=\n"); + + if (test_dlclose) { + // Imitate an attacker sneaking in an executable page where a dlclose()d + // library was loaded. This needs to pass w/o CFI, so for the testing + // purpose, we just copy the bytes of a "void f() {}" function back and + // forth. + void (*do_nothing)() = (void (*)())dlsym(handle, "do_nothing"); + assert(do_nothing); + save_code((char *)do_nothing); + + int res = dlclose(handle); + assert(res == 0); + + restore_code(); + + do_nothing(); // UB here + } else { + a->f(); // UB here + } + + // CFI-NOT: =2= + // CFI-CAST-NOT: =2= + // NCFI: =2= + fprintf(stderr, "=2=\n"); +} +#endif Index: test/cfi/cross-dso/shadow_is_read_only.cpp =================================================================== --- /dev/null +++ test/cfi/cross-dso/shadow_is_read_only.cpp @@ -0,0 +1,82 @@ +// RUN: %clangxx_cfi_dso -std=c++11 -g -DSHARED_LIB %s -fPIC -shared -o %t-cfi-so.so +// RUN: %clangxx -std=c++11 -g -DSHARED_LIB %s -fPIC -shared -o %t-nocfi-so.so +// RUN: %clangxx_cfi_dso -std=c++11 -g %s -o %t + +// RUN: %expect_crash %t start 2>&1 | FileCheck %s +// RUN: %expect_crash %t mmap 2>&1 | FileCheck %s +// RUN: %expect_crash %t dlopen %t-cfi-so.so 2>&1 | FileCheck %s +// RUN: %expect_crash %t dlclose %t-cfi-so.so 2>&1 | FileCheck %s +// RUN: %expect_crash %t dlopen %t-nocfi-so.so 2>&1 | FileCheck %s +// RUN: %expect_crash %t dlclose %t-nocfi-so.so 2>&1 | FileCheck %s + +// Tests that shadow is read-only most of the time. +// REQUIRES: cxxabi + +#include +#include +#include +#include +#include +#include +#include + +struct A { + virtual void f(); +}; + +#ifdef SHARED_LIB + +void A::f() {} + +extern "C" A *create_A() { return new A(); } + +#else + +constexpr unsigned kShadowGranularity = 12; +uintptr_t GetShadow(); + +void write_shadow(void *ptr) { + uintptr_t base = GetShadow(); + uint16_t *s = + (uint16_t *)(base + (((uintptr_t)ptr >> kShadowGranularity) << 1)); + fprintf(stderr, "going to crash\n"); + // CHECK: going to crash + *s = 42; + fprintf(stderr, "did not crash\n"); + // CHECK-NOT: did not crash + exit(1); +} + +int main(int argc, char *argv[]) { + assert(argc > 1); + const bool test_mmap = strcmp(argv[1], "mmap") == 0; + const bool test_start = strcmp(argv[1], "start") == 0; + const bool test_dlopen = strcmp(argv[1], "dlopen") == 0; + const bool test_dlclose = strcmp(argv[1], "dlclose") == 0; + const char *lib = argc > 2 ? argv[2] : nullptr; + + if (test_start) + write_shadow((void *)&main); + + if (test_mmap) { + void *p = mmap(nullptr, 1 << 20, PROT_READ | PROT_WRITE | PROT_EXEC, + MAP_PRIVATE | MAP_ANONYMOUS, 0, 0); + assert(p != MAP_FAILED); + write_shadow((char *)p + 100); + } else { + void *handle = dlopen(lib, RTLD_NOW); + assert(handle); + void *create_A = dlsym(handle, "create_A"); + assert(create_A); + + if (test_dlopen) + write_shadow(create_A); + + int res = dlclose(handle); + assert(res == 0); + + if (test_dlclose) + write_shadow(create_A); + } +} +#endif