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move mpk code to separate file, cleanup some of the interfaces
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@struct
struct committed Jul 21, 2019
1 parent 3cc6733 commit 53a6945
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Showing 5 changed files with 489 additions and 263 deletions.
6 changes: 3 additions & 3 deletions src/Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ library: clean
## Build a debug version of the library
library_debug: clean
mkdir -p ../build/
$(CC) $(CFLAGS) $(LIBRARY) $(DEBUG_FLAGS) mapguard.c vector.c -o ../build/libmapguard.so
$(CC) $(CFLAGS) $(LIBRARY) $(DEBUG_FLAGS) mapguard.c mapguard_mpk.c vector.c -o ../build/libmapguard.so

## Build the unit test
test: clean library
Expand All @@ -29,8 +29,8 @@ test: clean library
## Build a debug version of the unit test
debug_test: clean library_debug
mkdir -p ../build/
$(CC) $(CFLAGS) $(EXE_CFLAGS) $(DEBUG_FLAGS) mapguard_test.c vector.c -o ../build/mapguard_test -L../build/ -lmapguard
$(CC) $(CFLAGS) $(EXE_CFLAGS) $(DEBUG_FLAGS) mapguard_thread_test.c vector.c -o ../build/mapguard_thread_test -L../build/ -lmapguard -lpthread
$(CC) $(CFLAGS) $(EXE_CFLAGS) $(DEBUG_FLAGS) mapguard_test.c vector.c -o ../build/mapguard_test -L../build/ -lmapguard -ldl
$(CC) $(CFLAGS) $(EXE_CFLAGS) $(DEBUG_FLAGS) mapguard_thread_test.c vector.c -o ../build/mapguard_thread_test -L../build/ -lmapguard -lpthread -ldl

## Build the vector tests
vector_test:
Expand Down
276 changes: 27 additions & 249 deletions src/mapguard.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,8 @@ __attribute__((constructor)) void mapguard_ctor() {
g_real_pkey_mprotect = dlsym(RTLD_NEXT, "pkey_mprotect");
g_real_pkey_alloc = dlsym(RTLD_NEXT, "pkey_alloc");
g_real_pkey_free = dlsym(RTLD_NEXT, "pkey_free");
g_real_pkey_set = dlsym(RTLD_NEXT, "pkey_set");
g_real_pkey_get = dlsym(RTLD_NEXT, "pkey_get");
#endif

vector_init(&g_map_cache_vector);
Expand Down Expand Up @@ -60,10 +62,6 @@ int32_t env_to_int(char *string) {
return strtoul(p, NULL, 0);
}

inline __attribute__((always_inline)) void *get_base_page(void *addr) {
return (void *) ((uintptr_t) addr & ~(g_page_size-1));
}

/* Checks if we have a cache entry for this mapping */
void *is_mapguard_entry_cached(void *p, void *data) {
mapguard_cache_entry_t *mce = (mapguard_cache_entry_t *) p;
Expand All @@ -80,6 +78,11 @@ void *is_mapguard_entry_cached(void *p, void *data) {
return NULL;
}

mapguard_cache_entry_t *get_cache_entry(void *addr) {
mapguard_cache_entry_t *mce = (mapguard_cache_entry_t *) vector_for_each(&g_map_cache_vector, (vector_for_each_callback_t *) is_mapguard_entry_cached, addr);
return mce;
}

void *map_guard_page(void *addr) {
return g_real_mmap(get_base_page(addr), g_page_size, PROT_NONE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
}
Expand All @@ -106,7 +109,7 @@ void unmap_guard_pages(mapguard_cache_entry_t *mce) {
}

void map_bottom_guard_page(mapguard_cache_entry_t *mce) {
if(mce == NULL || mce->guard_bottom != 0) {
if(mce == NULL || mce->guard_bottom) {
return;
}

Expand All @@ -122,7 +125,7 @@ void map_bottom_guard_page(mapguard_cache_entry_t *mce) {
}

void map_top_guard_page(mapguard_cache_entry_t *mce) {
if(mce == NULL || mce->guard_top != 0) {
if(mce == NULL || mce->guard_top) {
return;
}

Expand All @@ -138,7 +141,7 @@ void map_top_guard_page(mapguard_cache_entry_t *mce) {
}

void map_guard_pages(mapguard_cache_entry_t *mce) {
if(mce->start == 0 && mce->size != 0) {
if(mce->start == 0 && mce->size) {
return;
}

Expand Down Expand Up @@ -217,7 +220,7 @@ int munmap(void *addr, size_t length) {

/* Remove tracked pages from the cache */
if(g_mapguard_policy.use_mapping_cache) {
mce = (mapguard_cache_entry_t *) vector_for_each(&g_map_cache_vector, (vector_for_each_callback_t *) is_mapguard_entry_cached, (void *) addr);
mce = get_cache_entry(addr);

if(mce) {
LOG("Found mapguard cache entry for mapping %p", mce->start);
Expand Down Expand Up @@ -254,17 +257,20 @@ int munmap(void *addr, size_t length) {
return ret;
}
} else {
ret = g_real_munmap(addr, length);

/* Continue tracking a failed unmapping */
if(ret != 0) {
return ret;
}
#ifdef MPK_SUPPORT
if(mce->pkey) {
/* This is a full unmapping so we call pkey_free */
g_real_pkey_set(mce->pkey, 0);
g_real_pkey_free(mce->pkey);
}
#endif
ret = g_real_munmap(addr, length);

/* Continue tracking a failed unmapping */
if(ret) {
return ret;
}

unmap_guard_pages(mce);
LOG("Deleting cache entry for %p", mce->start);
vector_delete_at(&g_map_cache_vector, mce->cache_index);
Expand Down Expand Up @@ -292,8 +298,7 @@ int mprotect(void *addr, size_t len, int prot) {

/* Disallow transition to/from X (requires the mapping cache) */
if(g_mapguard_policy.use_mapping_cache) {
mce = (mapguard_cache_entry_t *) vector_for_each(&g_map_cache_vector, (vector_for_each_callback_t *) is_mapguard_entry_cached, (void *) addr);

mce = get_cache_entry(addr);
#ifdef MPK_SUPPORT
if(mce != NULL && mce->xom_enabled == 0) {
#else
Expand Down Expand Up @@ -332,28 +337,12 @@ int mprotect(void *addr, size_t len, int prot) {
return ret;
}

/* Hook pkey_mprotect in libc */
int pkey_mprotect(void *addr, size_t len, int prot, int pkey) {
/* No support for other pkey callers just yet */
return ERROR;
}

int pkey_alloc(unsigned int flags, unsigned int access_rights) {
/* No support for other pkey callers just yet */
return ERROR;
}

int pkey_free(int pkey) {
/* No support for other pkey callers just yet */
return ERROR;
}

/* Hook mremap in libc */
void* mremap(void *__addr, size_t __old_len, size_t __new_len, int __flags, ...) {
void *map_ptr = g_real_mremap(__addr, __old_len, __new_len, __flags);

if(g_mapguard_policy.use_mapping_cache) {
mapguard_cache_entry_t *mce = (mapguard_cache_entry_t *) vector_for_each(&g_map_cache_vector, (vector_for_each_callback_t *) is_mapguard_entry_cached, (void *) __addr);
mapguard_cache_entry_t *mce = get_cache_entry(__addr);

/* We are remapping a previously tracked allocation. This
* means we may have to reallocate guard pages and update
Expand All @@ -376,21 +365,14 @@ void* mremap(void *__addr, size_t __old_len, size_t __new_len, int __flags, ...)
map_guard_pages(mce);

#ifdef MPK_SUPPORT
/* If this mapping had previously utilized MPK support we
* need to setup that up again */
/* If this mapping had previously utilized MPK
* support we need to setup that up again. We
* cheat and reuse the existing pkey and assume
* the desired access rights are the same */
if(mce->pkey) {
g_real_pkey_free(mce->pkey);
mce->pkey = g_real_pkey_alloc(0, mce->pkey_access_rights);

/* This shouldn't happen... */
if(mce->pkey == 0) {
LOG("Failed to allocate protection key for address %p", mce->start);
return map_ptr;
}

int32_t ret = g_real_pkey_mprotect(mce->start, mce->size, mce->current_prot, mce->pkey);

if(ret != 0) {
if(ret) {
LOG("Failed to call pkey_mprotect for address %p", mce->start);
}
}
Expand All @@ -400,207 +382,3 @@ void* mremap(void *__addr, size_t __old_len, size_t __new_len, int __flags, ...)

return map_ptr;
}

#ifdef MPK_SUPPORT

/* Memory Protection Keys is a feature on newer Intel x64 Skylake processors
* that allows a program set permission bits on a per-page mapping. The advantage
* of MPK over mprotect() is that its a lot faster. This feature of MapGuard
* has only been tested on AWS EC2 C5 instances and it may not even work there
* depending on your kernel version and program design.
*
* To know if your kernel supports MPK try the following:
* cat /proc/cpuinfo | grep -E 'pku|ospke'
*
* The Map Guard APIs that work with MPK always works terms of page ranges.
* This means for API functions like protect_mapping which take a start
* and end pointer we may end up protecting an entire region of memory
* and not just the page represented by the start pointer. Theres no easy
* way to implement this except for with explicit documentation detailing
* the implicit behavior.
*/

/* memcpy_xom - Allocates writeable memory, copies src_size bytes from src
* into those pages, and then marks the allocation execute only. Upon
* failure it returns MAP_FAILED. Upon success it returns a pointer to the
* Execute Only memory region */
void *memcpy_xom(size_t allocation_size, void *src, size_t src_size) {

if(g_mapguard_policy.use_mapping_cache == 0) {
LOG("Cannot allocate XOM memory without MG_USE_MAPPING_CACHE enabled");
return MAP_FAILED;
}

if(src == NULL || src_size == 0) {
LOG("XOM allocation failed, src is %p and src_size = %ld", src, src_size);
return MAP_FAILED;
}

if(src_size > allocation_size) {
LOG("XOM allocation failed, src size larger than allocation size")
return MAP_FAILED;
}

void *map_ptr = g_real_mmap(0x0, allocation_size, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);

if(map_ptr == MAP_FAILED) {
LOG("XOM mmap failed");
return MAP_FAILED;
}

memcpy(map_ptr, src, src_size);

mapguard_cache_entry_t *mce = (mapguard_cache_entry_t *) malloc(sizeof(mapguard_cache_entry_t));
memset(mce, 0x0, sizeof(mapguard_cache_entry_t));

mce->start = map_ptr;
mce->size = allocation_size;
mce->immutable_prot |= PROT_EXEC;
mce->current_prot = PROT_EXEC;
mce->xom_enabled = 1;
/* We use -1 here as a stand in for the kernels execute_only_pkey */
mce->pkey = -1;
mce->pkey_access_rights = PKEY_DISABLE_ACCESS;

int32_t ret = g_real_mprotect(map_ptr, allocation_size, PROT_EXEC);

if(ret != 0) {
LOG("XOM mprotect failed, unmapping memory");
g_real_munmap(map_ptr, allocation_size);
free(mce);
return MAP_FAILED;
}

mce->cache_index = vector_push(&g_map_cache_vector, mce);

return map_ptr;
}

int munmap_xom(void *addr, size_t length) {
mapguard_cache_entry_t *mce = (mapguard_cache_entry_t *) vector_for_each(&g_map_cache_vector, (vector_for_each_callback_t *) is_mapguard_entry_cached, (void *) addr);

if(mce != NULL) {
LOG("Found mapguard cache entry for mapping %p", mce->start);
g_real_pkey_free(mce->pkey);
vector_delete_at(&g_map_cache_vector, mce->cache_index);
free(mce);
} else {
return ERROR;
}

return OK;
}

/* addr - Address within a page range to protect
*
* This function derives the base page start is mapped in
* and then determines if Map Guard is currently tracking
* it. If so we check for an existing pkey or alloc a new
* one. A -1 return value means we are out of pkeys or
* the value of start was bad.
*
* If this function detects we are tracking an allocation
* of pages this address falls within the entire range will
* be protected with MPK, not just the page its on.
*/
int32_t protect_mapping(void *addr) {
if(addr == NULL) {
return ERROR;
}

mapguard_cache_entry_t *mce = (mapguard_cache_entry_t *) vector_for_each(&g_map_cache_vector, (vector_for_each_callback_t *) is_mapguard_entry_cached, addr);

if(mce == NULL) {
/* We aren't currently tracking these pages, so lets
* start doing that. We don't allocate guard pages
* because no r/w operations will take place here */
mce = new_mapguard_cache_entry();
mce->start = get_base_page(addr);
/* We only know a single address, so we default to 1 page */
mce->size = g_page_size;
mce->immutable_prot |= PROT_NONE;
mce->current_prot = PROT_NONE;
mce->cache_index = vector_push(&g_map_cache_vector, mce);
}

mce->pkey_access_rights = PKEY_DISABLE_ACCESS;

/* If there an existing key then we free it and allocate a new one */
if(mce->pkey != 0) {
g_real_pkey_free(mce->pkey);
pkeys_used--;
}

mce->pkey = g_real_pkey_alloc(0, mce->pkey_access_rights);

if(mce->pkey == 0) {
LOG("Failed to allocate protection key for address %p", mce->start);
return ERROR;
}

pkeys_used++;

int32_t ret = g_real_pkey_mprotect(mce->start, mce->size, PROT_NONE, mce->pkey);

if(ret != 0) {
LOG("Failed to call pkey_mprotect for address %p", mce->start);
return ret;
}

return OK;
}

int32_t unprotect_mapping(void *addr, int new_prot) {
if(addr == NULL) {
return ERROR;
}

mapguard_cache_entry_t *mce = (mapguard_cache_entry_t *) vector_for_each(&g_map_cache_vector, (vector_for_each_callback_t *) is_mapguard_entry_cached, addr);

if(mce != NULL && mce->pkey != 0) {
mprotect(get_base_page(addr), mce->size, new_prot);
mce->immutable_prot |= new_prot;
mce->current_prot = new_prot;
mce->pkey_access_rights = 0;
g_real_pkey_free(mce->pkey);
mce->pkey = 0;
}

return OK;
}

static int32_t map_guard_protect_code_callback(struct dl_phdr_info *info, size_t size, void *data) {
const char *lib_name = "unknown_object";

if(strlen(info->dlpi_name) != 0) {
lib_name = info->dlpi_name;
}

void *load_address = (void *) info->dlpi_addr;
int32_t ret = OK;

for(uint32_t i = 0; i < info->dlpi_phnum; i++) {
if(info->dlpi_phdr[i].p_type == PT_LOAD && (info->dlpi_phdr[i].p_flags & PF_X)) {
ret |= g_real_mprotect(load_address, info->dlpi_phdr[i].p_memsz, (int32_t) data);
}
}

return ret;
}

/* Uses the dynamic linker dl_iterate_phdr API to locate all
* currently mapped PT_LOAD segments with PF_X flags and then
* uses mprotect to mark them execute only */
int32_t protect_code() {
return dl_iterate_phdr(map_guard_protect_code_callback, (void *)PROT_EXEC);
}

/* Locate all currently mapped PT_LOAD segments with PF_X flags
* and mark them PROT_READ|PROT_EXEC. Its possible this will find
* segments of code that were not found when you called protect_code
* but that should be harmless */
int32_t unprotect_code() {
return dl_iterate_phdr(map_guard_protect_code_callback, (void *)(PROT_READ|PROT_EXEC));
}

#endif
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