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skip ELF image validation
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Gautham
parent
a9cb14668e
commit
850a7dab74
1 changed files with 0 additions and 165 deletions
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@ -199,170 +199,6 @@ static void GetOpts(int argc, char *argv[]) {
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exepath = argv[optind];
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}
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static void ValidateElfImage(Elf64_Ehdr *e, Elf64_Off esize, //
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const char *epath) {
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// validate elf header
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if (e->e_type != ET_EXEC && e->e_type != ET_DYN)
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Die(epath, "elf binary isn't an executable");
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if (!e->e_phnum)
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Die(epath, "elf executable needs at least one program header");
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if (e->e_phnum > 65534)
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Die(epath, "elf with more than 65534 phdrs not supported");
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if (e->e_phentsize != sizeof(Elf64_Phdr))
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Die(epath, "elf e_phentsize isn't sizeof(Elf64_Phdr)");
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if (e->e_phoff > esize)
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Die(epath, "elf program header offset points past image eof");
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if (e->e_phoff & 7)
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Die(epath, "elf e_phoff must be aligned on an 8-byte boundary");
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if (e->e_phoff + e->e_phoff + e->e_phnum * sizeof(Elf64_Phdr) > esize)
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Die(epath, "elf program header array overlaps image eof");
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// determine microprocessor page size requirement
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//
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// even though operating systems (windows) and c libraries (cosmo)
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// sometimes impose a larger page size requirement than the actual
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// microprocessor itself, the cpu page size is still the only page
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// size that actually matters when it comes to executable loading.
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unsigned long pagesz;
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if (e->e_machine == EM_AARCH64) {
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pagesz = 16384; // apple m1 (xnu, linux)
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} else { //
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pagesz = 4096; // x86-64, raspberry pi
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}
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// remove empty segment loads
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// empty loads should be inconsequential; linux ignores them
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// however they tend to trip up many systems such as openbsd
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int i, j;
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Elf64_Phdr *p = (Elf64_Phdr *)((char *)e + e->e_phoff);
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for (i = 0; i < e->e_phnum;) {
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if (p[i].p_type == PT_LOAD && !p[i].p_memsz) {
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if (i + 1 < e->e_phnum) {
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memmove(p + i, p + i + 1, (e->e_phnum - (i + 1)) * sizeof(*p));
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}
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--e->e_phnum;
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} else {
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++i;
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}
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}
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// oracle says loadable segment entries in the program header table
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// appear in ascending order, sorted on the p_vaddr member.
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int found_load = 0;
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Elf64_Addr last_vaddr = 0;
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for (i = 0; i < e->e_phnum; ++i) {
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if (p[i].p_type != PT_LOAD)
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continue;
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if (found_load && p[i].p_vaddr <= last_vaddr) {
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Die(epath, "ELF PT_LOAD segments must be ordered by p_vaddr");
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}
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last_vaddr = p[i].p_vaddr;
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found_load = 1;
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}
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if (!found_load) {
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Die(epath, "ELF must have at least one PT_LOAD segment");
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}
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// merge adjacent loads that are contiguous with equal protection
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for (i = 0; i + 1 < e->e_phnum;) {
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if (p[i].p_type == PT_LOAD && p[i + 1].p_type == PT_LOAD &&
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((p[i].p_flags & (PF_R | PF_W | PF_X)) ==
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(p[i + 1].p_flags & (PF_R | PF_W | PF_X))) &&
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((p[i].p_offset + p[i].p_filesz + (pagesz - 1)) & -pagesz) -
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(p[i + 1].p_offset & -pagesz) <=
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pagesz &&
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((p[i].p_vaddr + p[i].p_memsz + (pagesz - 1)) & -pagesz) -
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(p[i + 1].p_vaddr & -pagesz) <=
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pagesz) {
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p[i].p_memsz = (p[i + 1].p_vaddr + p[i + 1].p_memsz) - p[i].p_vaddr;
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p[i].p_filesz = (p[i + 1].p_offset + p[i + 1].p_filesz) - p[i].p_offset;
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if (i + 2 < e->e_phnum) {
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memmove(p + i + 1, p + i + 2, (e->e_phnum - (i + 2)) * sizeof(*p));
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}
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--e->e_phnum;
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} else {
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++i;
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}
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}
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// validate program headers
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bool found_entry = false;
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for (i = 0; i < e->e_phnum; ++i) {
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if (p[i].p_type == PT_INTERP) {
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Die(epath, "ELF has PT_INTERP which isn't supported");
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}
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if (p[i].p_type == PT_DYNAMIC) {
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Die(epath, "ELF has PT_DYNAMIC which isn't supported");
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}
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if (p[i].p_type != PT_LOAD) {
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continue;
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}
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if (!p[i].p_memsz) {
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Die(epath, "ELF PT_LOAD p_memsz was zero");
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}
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if (p[i].p_offset > esize) {
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Die(epath, "ELF PT_LOAD p_offset points past EOF");
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}
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if (p[i].p_filesz > p[i].p_memsz) {
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Die(epath, "ELF PT_LOAD p_filesz exceeds p_memsz");
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}
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if (p[i].p_align > 1 && (p[i].p_align & (p[i].p_align - 1))) {
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Die(epath, "ELF PT_LOAD p_align must be two power");
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}
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if (p[i].p_vaddr + p[i].p_memsz < p[i].p_vaddr ||
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p[i].p_vaddr + p[i].p_memsz + (pagesz - 1) < p[i].p_vaddr) {
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Die(epath, "ELF PT_LOAD p_vaddr + p_memsz overflow");
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}
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if (p[i].p_offset + p[i].p_filesz < p[i].p_offset ||
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p[i].p_offset + p[i].p_filesz + (pagesz - 1) < p[i].p_offset) {
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Die(epath, "ELF PT_LOAD p_offset + p_filesz overflow");
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}
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if (p[i].p_align > 1 && ((p[i].p_vaddr & (p[i].p_align - 1)) !=
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(p[i].p_offset & (p[i].p_align - 1)))) {
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Die(epath, "ELF p_vaddr incongruent w/ p_offset modulo p_align");
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}
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if ((p[i].p_vaddr & (pagesz - 1)) != (p[i].p_offset & (pagesz - 1))) {
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Die(epath, "ELF p_vaddr incongruent w/ p_offset modulo AT_PAGESZ");
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}
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if (p[i].p_offset + p[i].p_filesz > esize) {
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Die(epath, "ELF PT_LOAD p_offset and p_filesz overlaps image EOF");
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}
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Elf64_Off a = p[i].p_vaddr & -pagesz;
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Elf64_Off b = (p[i].p_vaddr + p[i].p_memsz + (pagesz - 1)) & -pagesz;
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for (j = i + 1; j < e->e_phnum; ++j) {
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if (p[j].p_type != PT_LOAD)
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continue;
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Elf64_Off c = p[j].p_vaddr & -pagesz;
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Elf64_Off d = (p[j].p_vaddr + p[j].p_memsz + (pagesz - 1)) & -pagesz;
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if (MAX(a, c) < MIN(b, d)) {
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Die(epath,
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"ELF PT_LOAD phdrs %d and %d overlap each others virtual memory");
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}
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}
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if (e->e_machine == EM_AARCH64 &&
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p[i].p_vaddr + p[i].p_memsz > 0x0001000000000000) {
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Die(epath, "this is an ARM ELF program but it loads to virtual"
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" memory addresses outside the legal range [0,2^48)");
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}
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if (e->e_machine == EM_NEXGEN32E &&
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!(-140737488355328 <= (Elf64_Sxword)p[i].p_vaddr &&
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(Elf64_Sxword)(p[i].p_vaddr + p[i].p_memsz) <= 140737488355328)) {
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Die(epath, "this is an x86-64 ELF program, but it loads to virtual"
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" memory addresses outside the legal range [-2^47,2^47)");
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}
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if ((p[i].p_flags & PF_X) && //
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p[i].p_vaddr <= e->e_entry &&
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e->e_entry < p[i].p_vaddr + p[i].p_memsz) {
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found_entry = 1;
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}
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}
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if (!found_entry) {
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Die(epath, "ELF entrypoint not found in PT_LOAD with PF_X");
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}
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}
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struct Input {
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union {
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char *map;
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@ -417,7 +253,6 @@ int main(int argc, char *argv[]) {
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GetOpts(argc, argv);
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OpenInput(exepath);
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ValidateElfImage(input.elf, input.size, input.path);
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rodata = FindElfSectionByName(
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input.elf, input.size,
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GetElfSectionNameStringTable(input.elf, input.size), ".rodata");
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