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-rw-r--r--linker/linker_phdr.cpp464
1 files changed, 233 insertions, 231 deletions
diff --git a/linker/linker_phdr.cpp b/linker/linker_phdr.cpp
index acd18cd..64dbb70 100644
--- a/linker/linker_phdr.cpp
+++ b/linker/linker_phdr.cpp
@@ -26,10 +26,13 @@
* SUCH DAMAGE.
*/
+#include "linker_phdr.h"
+
#include <errno.h>
#include <sys/mman.h>
-#include "linker_phdr.h"
+#include "linker.h"
+#include "linker_debug.h"
/**
TECHNICAL NOTE ON ELF LOADING.
@@ -112,66 +115,116 @@
MAYBE_MAP_FLAG((x), PF_R, PROT_READ) | \
MAYBE_MAP_FLAG((x), PF_W, PROT_WRITE))
-/* Load the program header table from an ELF file into a read-only private
- * anonymous mmap-ed block.
- *
- * Input:
- * fd -> file descriptor
- * phdr_offset -> file offset of phdr table
- * phdr_num -> number of entries in the table.
- *
- * Output:
- * phdr_mmap -> address of mmap block in memory.
- * phdr_memsize -> size of mmap block in memory.
- * phdr_table -> address of first entry in memory.
- *
- * Return:
- * -1 on error, or 0 on success.
- */
-int phdr_table_load(int fd,
- Elf32_Addr phdr_offset,
- Elf32_Half phdr_num,
- void** phdr_mmap,
- Elf32_Addr* phdr_size,
- const Elf32_Phdr** phdr_table)
-{
- Elf32_Addr page_min, page_max, page_offset;
- void* mmap_result;
-
- /* Just like the kernel, we only accept program header tables that
- * are smaller than 64KB. */
- if (phdr_num < 1 || phdr_num > 65536/sizeof(Elf32_Phdr)) {
- errno = EINVAL;
- return -1;
- }
-
- page_min = PAGE_START(phdr_offset);
- page_max = PAGE_END(phdr_offset + phdr_num*sizeof(Elf32_Phdr));
- page_offset = PAGE_OFFSET(phdr_offset);
-
- mmap_result = mmap(NULL,
- page_max - page_min,
- PROT_READ,
- MAP_PRIVATE,
- fd,
- page_min);
+ElfReader::ElfReader(const char* name, int fd)
+ : name_(name), fd_(fd),
+ phdr_num_(0), phdr_mmap_(NULL), phdr_table_(NULL), phdr_size_(0),
+ load_start_(NULL), load_size_(0), load_bias_(0),
+ loaded_phdr_(NULL) {
+}
- if (mmap_result == MAP_FAILED) {
- return -1;
- }
+ElfReader::~ElfReader() {
+ if (fd_ != -1) {
+ close(fd_);
+ }
+ if (phdr_mmap_ != NULL) {
+ munmap(phdr_mmap_, phdr_size_);
+ }
+}
- *phdr_mmap = mmap_result;
- *phdr_size = page_max - page_min;
- *phdr_table = (Elf32_Phdr*)((char*)mmap_result + page_offset);
+bool ElfReader::Load() {
+ return ReadElfHeader() &&
+ VerifyElfHeader() &&
+ ReadProgramHeader() &&
+ ReserveAddressSpace() &&
+ LoadSegments() &&
+ FindPhdr();
+}
- return 0;
+bool ElfReader::ReadElfHeader() {
+ ssize_t rc = TEMP_FAILURE_RETRY(read(fd_, &header_, sizeof(header_)));
+ if (rc < 0) {
+ DL_ERR("can't read file \"%s\": %s", name_, strerror(errno));
+ return false;
+ }
+ if (rc != sizeof(header_)) {
+ DL_ERR("\"%s\" is too small to be an ELF executable", name_);
+ return false;
+ }
+ return true;
}
-void phdr_table_unload(void* phdr_mmap, Elf32_Addr phdr_memsize)
-{
- munmap(phdr_mmap, phdr_memsize);
+bool ElfReader::VerifyElfHeader() {
+ if (header_.e_ident[EI_MAG0] != ELFMAG0 ||
+ header_.e_ident[EI_MAG1] != ELFMAG1 ||
+ header_.e_ident[EI_MAG2] != ELFMAG2 ||
+ header_.e_ident[EI_MAG3] != ELFMAG3) {
+ DL_ERR("\"%s\" has bad ELF magic", name_);
+ return false;
+ }
+
+ if (header_.e_ident[EI_CLASS] != ELFCLASS32) {
+ DL_ERR("\"%s\" not 32-bit: %d", name_, header_.e_ident[EI_CLASS]);
+ return false;
+ }
+ if (header_.e_ident[EI_DATA] != ELFDATA2LSB) {
+ DL_ERR("\"%s\" not little-endian: %d", name_, header_.e_ident[EI_DATA]);
+ return false;
+ }
+
+ if (header_.e_type != ET_DYN) {
+ DL_ERR("\"%s\" has unexpected e_type: %d", name_, header_.e_type);
+ return false;
+ }
+
+ if (header_.e_version != EV_CURRENT) {
+ DL_ERR("\"%s\" has unexpected e_version: %d", name_, header_.e_version);
+ return false;
+ }
+
+ if (header_.e_machine !=
+#ifdef ANDROID_ARM_LINKER
+ EM_ARM
+#elif defined(ANDROID_MIPS_LINKER)
+ EM_MIPS
+#elif defined(ANDROID_X86_LINKER)
+ EM_386
+#endif
+ ) {
+ DL_ERR("\"%s\" has unexpected e_machine: %d", name_, header_.e_machine);
+ return false;
+ }
+
+ return true;
}
+// Loads the program header table from an ELF file into a read-only private
+// anonymous mmap-ed block.
+bool ElfReader::ReadProgramHeader() {
+ phdr_num_ = header_.e_phnum;
+
+ // Like the kernel, we only accept program header tables that
+ // are smaller than 64KiB.
+ if (phdr_num_ < 1 || phdr_num_ > 65536/sizeof(Elf32_Phdr)) {
+ DL_ERR("\"%s\" has invalid e_phnum: %d", name_, phdr_num_);
+ return false;
+ }
+
+ Elf32_Addr page_min = PAGE_START(header_.e_phoff);
+ Elf32_Addr page_max = PAGE_END(header_.e_phoff + (phdr_num_ * sizeof(Elf32_Phdr)));
+ Elf32_Addr page_offset = PAGE_OFFSET(header_.e_phoff);
+
+ phdr_size_ = page_max - page_min;
+
+ void* mmap_result = mmap(NULL, phdr_size_, PROT_READ, MAP_PRIVATE, fd_, page_min);
+ if (mmap_result == MAP_FAILED) {
+ DL_ERR("\"%s\" phdr mmap failed: %s", name_, strerror(errno));
+ return false;
+ }
+
+ phdr_mmap_ = mmap_result;
+ phdr_table_ = reinterpret_cast<Elf32_Phdr*>(reinterpret_cast<char*>(mmap_result) + page_offset);
+ return true;
+}
/* Compute the extent of all loadable segments in an ELF program header
* table. This corresponds to the page-aligned size in bytes that needs to be
@@ -211,134 +264,100 @@ Elf32_Addr phdr_table_get_load_size(const Elf32_Phdr* phdr_table,
return max_vaddr - min_vaddr;
}
-/* Reserve a virtual address range big enough to hold all loadable
- * segments of a program header table. This is done by creating a
- * private anonymous mmap() with PROT_NONE.
- *
- * Input:
- * phdr_table -> program header table
- * phdr_count -> number of entries in the tables
- * Output:
- * load_start -> first page of reserved address space range
- * load_size -> size in bytes of reserved address space range
- * load_bias -> load bias, as described in technical note above.
- *
- * Return:
- * 0 on success, -1 otherwise. Error code in errno.
- */
-int
-phdr_table_reserve_memory(const Elf32_Phdr* phdr_table,
- size_t phdr_count,
- void** load_start,
- Elf32_Addr* load_size,
- Elf32_Addr* load_bias)
-{
- Elf32_Addr size = phdr_table_get_load_size(phdr_table, phdr_count);
- if (size == 0) {
- errno = EINVAL;
- return -1;
- }
-
- int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS;
- void* start = mmap(NULL, size, PROT_NONE, mmap_flags, -1, 0);
- if (start == MAP_FAILED) {
- return -1;
+// Reserve a virtual address range big enough to hold all loadable
+// segments of a program header table. This is done by creating a
+// private anonymous mmap() with PROT_NONE.
+bool ElfReader::ReserveAddressSpace() {
+ load_size_ = phdr_table_get_load_size(phdr_table_, phdr_num_);
+ if (load_size_ == 0) {
+ DL_ERR("\"%s\" has no loadable segments", name_);
+ return false;
+ }
+
+ int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS;
+ void* start = mmap(NULL, load_size_, PROT_NONE, mmap_flags, -1, 0);
+ if (start == MAP_FAILED) {
+ DL_ERR("couldn't reserve %d bytes of address space for \"%s\"", load_size_, name_);
+ return false;
+ }
+
+ load_start_ = start;
+ load_bias_ = 0;
+
+ for (size_t i = 0; i < phdr_num_; ++i) {
+ const Elf32_Phdr* phdr = &phdr_table_[i];
+ if (phdr->p_type == PT_LOAD) {
+ load_bias_ = reinterpret_cast<Elf32_Addr>(start) - PAGE_START(phdr->p_vaddr);
+ break;
}
-
- *load_start = start;
- *load_size = size;
- *load_bias = 0;
-
- for (size_t i = 0; i < phdr_count; ++i) {
- const Elf32_Phdr* phdr = &phdr_table[i];
- if (phdr->p_type == PT_LOAD) {
- *load_bias = (Elf32_Addr)start - PAGE_START(phdr->p_vaddr);
- break;
- }
- }
- return 0;
+ }
+ return true;
}
-/* Map all loadable segments in process' address space.
- * This assumes you already called phdr_table_reserve_memory to
- * reserve the address space range for the library.
- *
- * Input:
- * phdr_table -> program header table
- * phdr_count -> number of entries in the table
- * load_bias -> load offset.
- * fd -> input file descriptor.
- *
- * Return:
- * 0 on success, -1 otherwise. Error code in errno.
- */
-int
-phdr_table_load_segments(const Elf32_Phdr* phdr_table,
- int phdr_count,
- Elf32_Addr load_bias,
- int fd)
-{
- int nn;
+// Map all loadable segments in process' address space.
+// This assumes you already called phdr_table_reserve_memory to
+// reserve the address space range for the library.
+// TODO: assert assumption.
+bool ElfReader::LoadSegments() {
+ for (size_t i = 0; i < phdr_num_; ++i) {
+ const Elf32_Phdr* phdr = &phdr_table_[i];
- for (nn = 0; nn < phdr_count; nn++) {
- const Elf32_Phdr* phdr = &phdr_table[nn];
- void* seg_addr;
-
- if (phdr->p_type != PT_LOAD)
- continue;
-
- /* Segment addresses in memory */
- Elf32_Addr seg_start = phdr->p_vaddr + load_bias;
- Elf32_Addr seg_end = seg_start + phdr->p_memsz;
+ if (phdr->p_type != PT_LOAD) {
+ continue;
+ }
- Elf32_Addr seg_page_start = PAGE_START(seg_start);
- Elf32_Addr seg_page_end = PAGE_END(seg_end);
+ // Segment addresses in memory.
+ Elf32_Addr seg_start = phdr->p_vaddr + load_bias_;
+ Elf32_Addr seg_end = seg_start + phdr->p_memsz;
- Elf32_Addr seg_file_end = seg_start + phdr->p_filesz;
+ Elf32_Addr seg_page_start = PAGE_START(seg_start);
+ Elf32_Addr seg_page_end = PAGE_END(seg_end);
- /* File offsets */
- Elf32_Addr file_start = phdr->p_offset;
- Elf32_Addr file_end = file_start + phdr->p_filesz;
+ Elf32_Addr seg_file_end = seg_start + phdr->p_filesz;
- Elf32_Addr file_page_start = PAGE_START(file_start);
+ // File offsets.
+ Elf32_Addr file_start = phdr->p_offset;
+ Elf32_Addr file_end = file_start + phdr->p_filesz;
- seg_addr = mmap((void*)seg_page_start,
- file_end - file_page_start,
- PFLAGS_TO_PROT(phdr->p_flags),
- MAP_FIXED|MAP_PRIVATE,
- fd,
- file_page_start);
+ Elf32_Addr file_page_start = PAGE_START(file_start);
- if (seg_addr == MAP_FAILED) {
- return -1;
- }
-
- /* if the segment is writable, and does not end on a page boundary,
- * zero-fill it until the page limit. */
- if ((phdr->p_flags & PF_W) != 0 && PAGE_OFFSET(seg_file_end) > 0) {
- memset((void*)seg_file_end, 0, PAGE_SIZE - PAGE_OFFSET(seg_file_end));
- }
+ void* seg_addr = mmap((void*)seg_page_start,
+ file_end - file_page_start,
+ PFLAGS_TO_PROT(phdr->p_flags),
+ MAP_FIXED|MAP_PRIVATE,
+ fd_,
+ file_page_start);
+ if (seg_addr == MAP_FAILED) {
+ DL_ERR("couldn't map \"%s\" segment %d: %s", name_, i, strerror(errno));
+ return false;
+ }
- seg_file_end = PAGE_END(seg_file_end);
+ // if the segment is writable, and does not end on a page boundary,
+ // zero-fill it until the page limit.
+ if ((phdr->p_flags & PF_W) != 0 && PAGE_OFFSET(seg_file_end) > 0) {
+ memset((void*)seg_file_end, 0, PAGE_SIZE - PAGE_OFFSET(seg_file_end));
+ }
- /* seg_file_end is now the first page address after the file
- * content. If seg_end is larger, we need to zero anything
- * between them. This is done by using a private anonymous
- * map for all extra pages.
- */
- if (seg_page_end > seg_file_end) {
- void* zeromap = mmap((void*)seg_file_end,
- seg_page_end - seg_file_end,
- PFLAGS_TO_PROT(phdr->p_flags),
- MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
- -1,
- 0);
- if (zeromap == MAP_FAILED) {
- return -1;
- }
- }
+ seg_file_end = PAGE_END(seg_file_end);
+
+ // seg_file_end is now the first page address after the file
+ // content. If seg_end is larger, we need to zero anything
+ // between them. This is done by using a private anonymous
+ // map for all extra pages.
+ if (seg_page_end > seg_file_end) {
+ void* zeromap = mmap((void*)seg_file_end,
+ seg_page_end - seg_file_end,
+ PFLAGS_TO_PROT(phdr->p_flags),
+ MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
+ -1,
+ 0);
+ if (zeromap == MAP_FAILED) {
+ DL_ERR("couldn't zero fill \"%s\" gap: %s", name_, strerror(errno));
+ return false;
+ }
}
- return 0;
+ }
+ return true;
}
/* Used internally. Used to set the protection bits of all loaded segments
@@ -577,72 +596,55 @@ phdr_table_get_dynamic_section(const Elf32_Phdr* phdr_table,
}
}
-/* Return the address of the program header table as it appears in the loaded
- * segments in memory. This is in contrast with the input 'phdr_table' which
- * is temporary and will be released before the library is relocated.
- *
- * Input:
- * phdr_table -> program header table
- * phdr_count -> number of entries in tables
- * load_bias -> load bias
- * Return:
- * Address of loaded program header table on success (it has
- * 'phdr_count' entries), or NULL on failure (no error code).
- */
-const Elf32_Phdr*
-phdr_table_get_loaded_phdr(const Elf32_Phdr* phdr_table,
- int phdr_count,
- Elf32_Addr load_bias)
-{
- const Elf32_Phdr* phdr = phdr_table;
- const Elf32_Phdr* phdr_limit = phdr + phdr_count;
- Elf32_Addr loaded = 0;
- Elf32_Addr loaded_end;
+// Returns the address of the program header table as it appears in the loaded
+// segments in memory. This is in contrast with 'phdr_table_' which
+// is temporary and will be released before the library is relocated.
+bool ElfReader::FindPhdr() {
+ const Elf32_Phdr* phdr_limit = phdr_table_ + phdr_num_;
- /* If there is a PT_PHDR, use it directly */
- for (phdr = phdr_table; phdr < phdr_limit; phdr++) {
- if (phdr->p_type == PT_PHDR) {
- loaded = load_bias + phdr->p_vaddr;
- goto CHECK;
- }
+ // If there is a PT_PHDR, use it directly.
+ for (const Elf32_Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
+ if (phdr->p_type == PT_PHDR) {
+ return CheckPhdr(load_bias_ + phdr->p_vaddr);
}
-
- /* Otherwise, check the first loadable segment. If its file offset
- * is 0, it starts with the ELF header, and we can trivially find the
- * loaded program header from it. */
- for (phdr = phdr_table; phdr < phdr_limit; phdr++) {
- if (phdr->p_type == PT_LOAD) {
- if (phdr->p_offset == 0) {
- Elf32_Addr elf_addr = load_bias + phdr->p_vaddr;
- const Elf32_Ehdr* ehdr = (const Elf32_Ehdr*)(void*)elf_addr;
- Elf32_Addr offset = ehdr->e_phoff;
- loaded = (Elf32_Addr)ehdr + offset;
- goto CHECK;
- }
- break;
- }
+ }
+
+ // Otherwise, check the first loadable segment. If its file offset
+ // is 0, it starts with the ELF header, and we can trivially find the
+ // loaded program header from it.
+ for (const Elf32_Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
+ if (phdr->p_type == PT_LOAD) {
+ if (phdr->p_offset == 0) {
+ Elf32_Addr elf_addr = load_bias_ + phdr->p_vaddr;
+ const Elf32_Ehdr* ehdr = (const Elf32_Ehdr*)(void*)elf_addr;
+ Elf32_Addr offset = ehdr->e_phoff;
+ return CheckPhdr((Elf32_Addr)ehdr + offset);
+ }
+ break;
}
+ }
- /* We didn't find it, let the client know. He may be able to
- * keep a copy of the input phdr_table instead. */
- return NULL;
-
-CHECK:
- /* Ensure that our program header is actually within a loadable
- * segment. This should help catch badly-formed ELF files that
- * would cause the linker to crash later when trying to access it.
- */
- loaded_end = loaded + phdr_count*sizeof(Elf32_Phdr);
-
- for (phdr = phdr_table; phdr < phdr_limit; phdr++) {
- if (phdr->p_type != PT_LOAD)
- continue;
- Elf32_Addr seg_start = phdr->p_vaddr + load_bias;
- Elf32_Addr seg_end = phdr->p_filesz + seg_start;
+ DL_ERR("can't find loaded phdr for \"%s\"", name_);
+ return false;
+}
- if (seg_start <= loaded && loaded_end <= seg_end) {
- return (const Elf32_Phdr*)loaded;
- }
+// Ensures that our program header is actually within a loadable
+// segment. This should help catch badly-formed ELF files that
+// would cause the linker to crash later when trying to access it.
+bool ElfReader::CheckPhdr(Elf32_Addr loaded) {
+ const Elf32_Phdr* phdr_limit = phdr_table_ + phdr_num_;
+ Elf32_Addr loaded_end = loaded + (phdr_num_ * sizeof(Elf32_Phdr));
+ for (Elf32_Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
+ if (phdr->p_type != PT_LOAD) {
+ continue;
+ }
+ Elf32_Addr seg_start = phdr->p_vaddr + load_bias_;
+ Elf32_Addr seg_end = phdr->p_filesz + seg_start;
+ if (seg_start <= loaded && loaded_end <= seg_end) {
+ loaded_phdr_ = reinterpret_cast<const Elf32_Phdr*>(loaded);
+ return true;
}
- return NULL;
+ }
+ DL_ERR("\"%s\" loaded phdr %x not in loadable segment", name_, loaded);
+ return false;
}
generated by cgit v1.1 at 2024-09-27 02:27:51 +0000