├── .gitignore ├── LICENSE ├── Makefile ├── README.md └── src ├── cpuid.c ├── cpuid.h ├── cpuid.inc ├── library.c ├── library.h ├── loader.c ├── loader.h ├── syscalls.c └── syscalls.h /.gitignore: -------------------------------------------------------------------------------- 1 | *.o 2 | *.so 3 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /Makefile: -------------------------------------------------------------------------------- 1 | CFLAGS += -g -O2 -fPIC -pie -Wall -fno-stack-protector -fvisibility=hidden -fno-builtin 2 | LDFLAGS += -fPIC -pie -static -nostdlib -Wl,-z,relro -Wl,-z,initfirst -Wl,-e_start 3 | 4 | DEPS = $(wildcard src/*.h) 5 | SOURCES = $(wildcard src/*.c) 6 | OBJECTS = $(SOURCES:.c=.o) 7 | TARGET = libcpuidoverride.so 8 | 9 | $(TARGET): $(OBJECTS) $(DEPS) 10 | $(CC) $(OBJECTS) $(LDFLAGS) -o $@ 11 | 12 | %.o: %.c $(DEPS) 13 | $(CC) -c $(CFLAGS) $< -o $@ 14 | 15 | %.o: %.c $(DEPS) 16 | $(CC) -c $(CFLAGS) $< -o $@ 17 | 18 | all: $(SOURCES) $(TARGET) 19 | 20 | .PHONY: clean 21 | 22 | clean: 23 | rm -f $(OBJECTS) $(TARGET) 24 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # libcpuidoverride 2 | 3 | A shim dynamic loader for overriding CPUID, using processor support for CPUID faulting on Ivy Bridge+, and the Linux kernel support for `ARCH_GET_CPUID` / `ARCH_SET_CPUID` subfunctions on 4.12+. This was implemented using a shim dynamic loader instead of e.g. `LD_PRELOAD`, because glibc 2.26+ performs CPU feature detection within the dynamic loader itself, which is too early to intercept with `LD_PRELOAD`. 4 | 5 | Writeup: https://www.dcddcc.com/blog/2019-05-01-processor-cpuid-faulting-and-dynamic-loader-interposing.html 6 | 7 | Overridable CPUID features: [`SSE`](https://en.wikipedia.org/wiki/Streaming_SIMD_Extensions), [`SSE2`](https://en.wikipedia.org/wiki/SSE2), [`SSE3`](https://en.wikipedia.org/wiki/SSE3), [`SSSE3`](https://en.wikipedia.org/wiki/SSSE3), [`SSE41`](https://en.wikipedia.org/wiki/SSE4#SSE4.1), [`SSE42`](https://en.wikipedia.org/wiki/SSE4#SSE4.2), [`AVX`](https://en.wikipedia.org/wiki/Advanced_Vector_Extensions), [`AVX2`](https://en.wikipedia.org/wiki/Advanced_Vector_Extensions#AVX2), [`AVX512`](https://en.wikipedia.org/wiki/AVX-512), [`HLE`](https://en.wikipedia.org/wiki/Transactional_Synchronization_Extensions#Hardware_Lock_Elision), [`RTM`](https://en.wikipedia.org/wiki/Transactional_Synchronization_Extensions#Restricted_Transactional_Memory). 8 | 9 | ## Usage 10 | 11 | ``` 12 | cp 13 | patchelf --set-interpreter /libcpuidoverride.so 14 | NO_=1 15 | ``` 16 | 17 | For example, to disable AVX2 for the `cpuid` binary: 18 | 19 | ``` 20 | cp `which cpuid` patched_cpuid 21 | patchelf --set-interpreter `pwd`/libcpuidoverride.so patched_cpuid 22 | NO_AVX2=1 patched_cpuid 23 | ``` 24 | 25 | Alternatively, build with `-Wl,--dynamic-linker=/libcpuidoverride.so`. 26 | -------------------------------------------------------------------------------- /src/cpuid.c: -------------------------------------------------------------------------------- 1 | #define _GNU_SOURCE 2 | 3 | #include 4 | #include 5 | #include 6 | #include 7 | 8 | #include 9 | #include 10 | #include 11 | 12 | #include "cpuid.h" 13 | #include "library.h" 14 | #include "syscalls.h" 15 | 16 | /* List of disabled CPUID features */ 17 | feature_t disabled; 18 | /* Previous signal handler */ 19 | struct sigaction old_handler; 20 | 21 | void get_features(feature_t *disabled) { 22 | /* Mark feature disabled if environment variable defined */ 23 | #define FEATURE(name, leaf, subleaf, reg, bit) if (my_getenv("NO_" #name)) { disabled->name = 1; my_puts("Overriding feature " #name "!"); } 24 | #define FEATURE2(name, leaf, subleaf, reg, bit) /* nothing */ 25 | #include "cpuid.inc" 26 | #undef FEATURE2 27 | #undef FEATURE 28 | } 29 | 30 | void sigsegv_handler(int signal, siginfo_t *info, void *ucontext) { 31 | /* Check if CPUID was executed */ 32 | const uint8_t *ip = (const uint8_t *)GET_REGISTER(ucontext, IP); 33 | if (info->si_code == SI_KERNEL && ip[0] == CPUID_INSN0 && ip[1] == CPUID_INSN1) { 34 | unsigned int AX, BX, CX, DX; 35 | greg_t leaf = GET_REGISTER(ucontext, AX), subleaf = GET_REGISTER(ucontext, CX); 36 | 37 | my_puts("Intercepted call to CPUID!"); 38 | 39 | // FIXME: May be racy. Either pre-cache CPUID values, or clone a child to retrieve the actual value 40 | /* Disable CPUID faulting */ 41 | if (my_arch_prctl(ARCH_SET_CPUID, 1) < 0) { 42 | my_puts("Failed to disable CPUID faulting!"); 43 | my_abort(); 44 | } 45 | 46 | /* Obtain the actual CPUID */ 47 | __cpuid_count(leaf, subleaf, AX, BX, CX, DX); 48 | 49 | /* Mask off anything that should be disabled */ 50 | int subleaf_valid = SUBLEAF_LEAVES(leaf); 51 | 52 | #define FEATURE(name, lf, slf, reg, bit) if (lf == leaf && (!subleaf_valid || slf == subleaf) && disabled.name) { reg &= ~(bit); my_puts("Hiding feature " #name "!"); } 53 | #define FEATURE2(name, leaf, subleaf, reg, bit) FEATURE(name, leaf, subleaf, reg, bit) 54 | #include "cpuid.inc" 55 | #undef FEATURE2 56 | #undef FEATURE 57 | 58 | /* Emulate the behavior of CPUID */ 59 | GET_REGISTER(ucontext, IP) += 2; 60 | GET_REGISTER(ucontext, AX) = AX; 61 | GET_REGISTER(ucontext, BX) = BX; 62 | GET_REGISTER(ucontext, CX) = CX; 63 | GET_REGISTER(ucontext, DX) = DX; 64 | 65 | /* Re-enable CPUID faulting */ 66 | if (my_arch_prctl(ARCH_SET_CPUID, 0) < 0) { 67 | my_puts("Failed to re-enable CPUID faulting!"); 68 | my_abort(); 69 | } 70 | } else { 71 | /* Call the previous signal handler */ 72 | if (old_handler.sa_flags & SA_SIGINFO && old_handler.sa_sigaction) 73 | old_handler.sa_sigaction(signal, info, ucontext); 74 | else if (old_handler.sa_handler) 75 | old_handler.sa_handler(signal); 76 | else { 77 | /* Disable this signal handler */ 78 | struct sigaction new = { 79 | .sa_handler = SIG_DFL, 80 | .sa_flags = SA_SIGINFO, 81 | }; 82 | if (my_sigaction(SIGSEGV, &new, NULL) < 0) { 83 | my_puts("Failed to change SIGSEGV signal handler!"); 84 | my_abort(); 85 | } 86 | 87 | /* Signal is fatal, so just re-raise it */ 88 | my_tgkill(my_getpid(), my_gettid(), SIGSEGV); 89 | } 90 | } 91 | } 92 | 93 | int hook_cpuid() { 94 | /* Determine which CPUID features should be disabled */ 95 | get_features(&disabled); 96 | 97 | /* Set the signal handler for SIGSEGV */ 98 | struct sigaction new = { 99 | .sa_sigaction = sigsegv_handler, 100 | .sa_flags = SA_SIGINFO, 101 | }; 102 | if (my_sigaction(SIGSEGV, &new, &old_handler) < 0) { 103 | my_puts("Failed to register SIGSEGV handler!"); 104 | return 0; 105 | } 106 | 107 | /* Enable CPUID faulting */ 108 | if (my_arch_prctl(ARCH_SET_CPUID, 0) < 0) { 109 | my_puts("Failed to enable CPUID faulting!"); 110 | return 0; 111 | } 112 | 113 | return 1; 114 | } 115 | -------------------------------------------------------------------------------- /src/cpuid.h: -------------------------------------------------------------------------------- 1 | #ifndef __CPUID_H__ 2 | #define __CPUID_H__ 3 | 4 | #include 5 | #include 6 | 7 | /* Access to registers from context */ 8 | #ifdef __x86_64__ 9 | # define GET_REGISTER(uctx, reg) ((ucontext_t *)uctx)->uc_mcontext.gregs[REG_R##reg] 10 | #elif defined(__i386__) 11 | # define GET_REGISTER(uctx, reg) ((ucontext_t *)uctx)->uc_mcontext.gregs[REG_E##reg] 12 | #else 13 | # error "Unsupported architecture!" 14 | #endif 15 | 16 | /* Define feature bits for compatibility with older GCC versions */ 17 | #ifdef __GNUC__ 18 | # if GCC_VERSION < 80100 19 | # define bit_AVX512VBMI2 (1 << 6) 20 | # define bit_AVX512VNNI (1 << 11) 21 | # define bit_AVX512BITALG (1 << 12) 22 | # endif /* GCC_VERSION < 8.1.0 */ 23 | #endif /* __GNUC__ */ 24 | 25 | /* Raw values of the CPUID instruction */ 26 | #define CPUID_INSN0 0x0f 27 | #define CPUID_INSN1 0xa2 28 | 29 | /* Leaves that contain subleaves */ 30 | #define SUBLEAF_LEAVES(x) ((x) == 0x04 || (x) == 0x07 || (x) == 0x0b || (x) == 0x0d || (x) == 0x0f || (x) == 0x10 || (x) == 0x12 || (x) == 0x14 || (x) == 0x17 || (x) == 0x18 || (x) == 0x1f) 31 | 32 | /* Structure of supported features */ 33 | typedef struct { 34 | #define FEATURE(name, leaf, subleaf, reg, bit) bool name; 35 | #define FEATURE2(name, leaf, subleaf, reg, bit) /* nothing */ 36 | #include "cpuid.inc" 37 | #undef FEATURE2 38 | #undef FEATURE 39 | } feature_t; 40 | 41 | int hook_cpuid(); 42 | 43 | #endif /* __CPUID_H__ */ 44 | -------------------------------------------------------------------------------- /src/cpuid.inc: -------------------------------------------------------------------------------- 1 | FEATURE(SSE, 1, 0, DX, bit_SSE) \ 2 | FEATURE(SSE2, 1, 0, DX, bit_SSE2) \ 3 | FEATURE(SSE3, 1, 0, CX, bit_SSE3) \ 4 | FEATURE(SSSE3, 1, 0, CX, bit_SSSE3) \ 5 | FEATURE(SSE41, 1, 0, CX, bit_SSE4_1) \ 6 | FEATURE(SSE42, 1, 0, CX, bit_SSE4_2) \ 7 | FEATURE(AVX, 1, 0, CX, bit_AVX) \ 8 | FEATURE(AVX2, 7, 0, BX, bit_AVX2) \ 9 | FEATURE(AVX512, 7, 0, BX, bit_AVX512F | bit_AVX512DQ | bit_AVX512IFMA | bit_AVX512PF | bit_AVX512ER | bit_AVX512CD | bit_AVX512BW | bit_AVX512VL) \ 10 | FEATURE2(AVX512, 7, 0, CX, bit_AVX512VBMI | bit_AVX512VBMI2 | bit_AVX512VNNI | bit_AVX512BITALG | bit_AVX512VPOPCNTDQ) \ 11 | FEATURE2(AVX512, 7, 0, DX, bit_AVX5124VNNIW | bit_AVX5124FMAPS) \ 12 | FEATURE(HLE, 7, 0, BX, bit_HLE) \ 13 | FEATURE(RTM, 7, 0, BX, bit_RTM) 14 | -------------------------------------------------------------------------------- /src/library.c: -------------------------------------------------------------------------------- 1 | #include 2 | #include 3 | #include 4 | #include 5 | #include 6 | 7 | #include "library.h" 8 | #include "syscalls.h" 9 | 10 | extern const char **envp; 11 | 12 | #ifdef __x86_64__ 13 | # define STRINGIFY_(x) #x 14 | # define STRINGIFY(x) STRINGIFY_(x) 15 | 16 | # define SA_RESTORER 0x04000000 17 | 18 | /* See RESTORE2 in glibc/sysdeps/unix/sysv/linux//sigaction.c */ 19 | void __restore_rt(); 20 | 21 | __asm__ ("\n\ 22 | .global __restore_rt\n\ 23 | .type __restore_rt,@function\n\ 24 | __restore_rt:\n\ 25 | mov $" STRINGIFY(SYS_rt_sigreturn) ", %eax\n\ 26 | syscall\n\ 27 | "); 28 | #else 29 | # error "Unsupported architecture!" 30 | #endif 31 | 32 | void my_abort() { 33 | // FIXME: Unblock SIGABRT 34 | my_tgkill(my_getpid(), my_gettid(), SIGABRT); 35 | } 36 | 37 | const char *my_getenv(const char *name) { 38 | const char **env = envp; 39 | 40 | while (*env) { 41 | if (!my_strcmp(*env, name)) { 42 | size_t len = my_strlen(name); 43 | if ((*env)[len] == '=') 44 | return &(*env)[len + 1]; 45 | } 46 | 47 | ++env; 48 | } 49 | 50 | return NULL; 51 | } 52 | 53 | int my_memcmp(const void *ptr1, const void *ptr2, size_t sz) { 54 | for (unsigned int i = 0; i < sz; ++i) { 55 | const uint8_t p1 = ((const uint8_t *)ptr1)[i], p2 = ((const uint8_t *)ptr2)[i]; 56 | if (p1 != p2) 57 | return p1 < p2 ? -1 : 1; 58 | } 59 | 60 | return 0; 61 | } 62 | 63 | int my_putchar(int character) { 64 | uint8_t c = character; 65 | 66 | if (my_write(STDOUT_FILENO, &c, 1) < 0) 67 | return EOF; 68 | 69 | return character; 70 | } 71 | 72 | int my_puts(const char *str) { 73 | if (my_write(STDOUT_FILENO, str, my_strlen(str)) < 0) 74 | return EOF; 75 | 76 | if (my_putchar('\n') == EOF) 77 | return EOF; 78 | 79 | return 1; 80 | } 81 | 82 | int my_sigaction(int signum, const struct sigaction *act, struct sigaction *old_act) { 83 | struct kernel_sigaction kact, kold_act; 84 | 85 | if (act) { 86 | kact.k_sa_handler = act->sa_handler; 87 | #ifdef __x86_64__ 88 | kact.sa_flags = act->sa_flags | SA_RESTORER; 89 | kact.sa_restorer = __restore_rt; 90 | #else 91 | kact.sa_flags = act->sa_flags; 92 | #endif /* __x86_64__ */ 93 | kact.sa_mask = act->sa_mask; 94 | } 95 | 96 | /* Note: Documentation says to use sizeof(sigset_t) = 128, but this will result in -EINVAL */ 97 | /* See __libc_sigaction in glibc/sysdeps/unix/sysv/linux/sigaction.c */ 98 | int ret = my_rt_sigaction(signum, &kact, old_act ? &kold_act : NULL, NSIG / 8); 99 | 100 | if (ret && old_act) { 101 | old_act->sa_handler = kold_act.k_sa_handler; 102 | #ifdef __x86_64__ 103 | old_act->sa_flags = kold_act.sa_flags & ~SA_RESTORER; 104 | #else 105 | old_act->sa_flags = kold_act.sa_flag; 106 | #endif /* __x86_64__ */ 107 | old_act->sa_mask = kold_act.sa_mask; 108 | } 109 | 110 | return ret; 111 | } 112 | 113 | int my_strcmp(const char *str1, const char *str2) { 114 | char c1, c2; 115 | 116 | while ((c1 = *str1++) && (c2 = *str2++)) { 117 | if (c1 != c2) 118 | return c1 < c2 ? -1 : 1; 119 | } 120 | 121 | return 0; 122 | } 123 | 124 | size_t my_strlen(const char *str) { 125 | size_t sz = 0; 126 | 127 | while (*str++) 128 | ++sz; 129 | 130 | return sz; 131 | } 132 | 133 | void my_strncpy(char *dst, const char *src, size_t sz) { 134 | int done = 0; 135 | 136 | for (unsigned int i = 0; i < sz; ++i) { 137 | if (!done) { 138 | const char c = src[i]; 139 | done = !c; 140 | dst[i] = c; 141 | } else 142 | dst[i] = '\0'; 143 | } 144 | } 145 | -------------------------------------------------------------------------------- /src/library.h: -------------------------------------------------------------------------------- 1 | #ifndef __STDLIB_H__ 2 | #define __STDLIB_H__ 3 | 4 | #include 5 | #include 6 | 7 | void my_abort(); 8 | 9 | const char *my_getenv(const char *name); 10 | 11 | int my_memcmp(const void *ptr1, const void *ptr2, size_t sz); 12 | 13 | int my_putchar(int character); 14 | 15 | int my_puts(const char *str); 16 | 17 | int my_sigaction(int signum, const struct sigaction *act, struct sigaction *old_act); 18 | 19 | int my_strcmp(const char *str1, const char *str2); 20 | 21 | size_t my_strlen(const char *str); 22 | 23 | void my_strncpy(char *dst, const char *src, size_t sz); 24 | 25 | #endif /* __STDLIB_H__ */ 26 | -------------------------------------------------------------------------------- /src/loader.c: -------------------------------------------------------------------------------- 1 | #include 2 | #include 3 | #include 4 | 5 | #include 6 | 7 | #include "cpuid.h" 8 | #include "library.h" 9 | #include "loader.h" 10 | #include "syscalls.h" 11 | 12 | int argc; 13 | const char **argv, **envp; 14 | const Elf_auxv_t *auxv; 15 | 16 | /* Architecture-specific definitions */ 17 | /* See RTLD_START in glibc/sysdeps//dl-machine.h */ 18 | #ifdef __x86_64__ 19 | __asm__ ("\n\ 20 | .global _start\n\ 21 | .type _start,@function\n\ 22 | _start:\n\ 23 | mov %rsp, %rdi\n\ 24 | call loader_init\n\ 25 | jmp *%rax\n\ 26 | "); 27 | #else 28 | # error "Unsupported architecture!" 29 | #endif 30 | 31 | /* Parse the stack set up by the kernel ELF loader */ 32 | /* See create_elf_tables in linux/fs/binfmt_elf.c */ 33 | void elf_stack_parse(Elf_Addr *stack) { 34 | int argc = stack[0]; 35 | argv = (const char **)&stack[1]; 36 | envp = (const char **)&stack[1 + argc + 1]; 37 | while (*envp++) { }; 38 | auxv = (Elf_auxv_t *)envp; 39 | envp = (const char **)&stack[1 + argc + 1]; 40 | } 41 | 42 | /* Parse the auxiliary vector and PT_INTERP program header */ 43 | void elf_auxv_parse(unsigned int *page_sz, uint8_t **rand) { 44 | while (auxv && auxv->a_type != AT_NULL) { 45 | if (auxv->a_type == AT_PAGESZ) { 46 | *page_sz = auxv->a_un.a_val; 47 | } else if (auxv->a_type == AT_RANDOM) { 48 | *rand = (uint8_t *)auxv->a_un.a_val; 49 | } 50 | 51 | ++auxv; 52 | } 53 | } 54 | 55 | /* Validate the ELF header */ 56 | int elf_ehdr_validate(const Elf_Ehdr *ehdr, bool exec) { 57 | return !my_memcmp(ehdr->e_ident, ELFMAG, SELFMAG) && ((exec && ehdr->e_type == ET_EXEC) || ehdr->e_type == ET_DYN) && GET_ELF_MACHINE(ehdr->e_machine) && ehdr->e_ehsize == sizeof(Elf_Ehdr) && ehdr->e_phentsize == sizeof(Elf_Phdr); 58 | } 59 | 60 | /* Fetch the interpreter offset from the ELF program header PT_INTERP */ 61 | Elf_Off elf_phdr_interpreter(const Elf_Phdr *phdr, unsigned int num_phdr) { 62 | for (unsigned int i = 0; i < num_phdr; ++i) { 63 | if (phdr[i].p_type == PT_INTERP) 64 | return phdr[i].p_offset; 65 | } 66 | 67 | return 0; 68 | } 69 | 70 | /* Convert the ELF segment flags into mmap access permissions */ 71 | int elf_phdr_flags_prot(Elf_Word flags) { 72 | return (flags & PF_R ? PROT_READ : PROT_NONE) | (flags & PF_W ? PROT_WRITE : PROT_NONE) | (flags & PF_X ? PROT_EXEC : PROT_NONE); 73 | } 74 | 75 | /* Load all ELF program header PT_LOAD into memory, and handle executable stack from program header PT_GNU_STACK */ 76 | void elf_phdr_load(const Elf_Phdr *phdr, unsigned int num_phdr, int fd, unsigned long base, void *stack, unsigned int page_sz) { 77 | /* See executable_stack in linux/fs/binfmt_elf.c */ 78 | unsigned int stack_prot = PF_R | PF_W | PF_X; 79 | 80 | for (unsigned int i = 0; i < num_phdr; ++i) { 81 | if (phdr[i].p_type == PT_LOAD) { 82 | /* Map in the page from the file */ 83 | void *addr = my_mmap((void *)(ALIGN(base + phdr[i].p_vaddr, page_sz)), phdr[i].p_vaddr - ALIGN(phdr[i].p_vaddr, page_sz) + phdr[i].p_filesz, elf_phdr_flags_prot(phdr[i].p_flags), MAP_FIXED_NOREPLACE | MAP_PRIVATE, fd, ALIGN(phdr[i].p_offset, page_sz)); 84 | if (addr == MAP_FAILED) { 85 | my_puts("Failed to map page from file!"); 86 | my_abort(); 87 | } 88 | 89 | /* Map in additional anonymous pages, if necessary */ 90 | /* See load_elf_binary in linux/fs/binfmt_elf.c */ 91 | if (phdr[i].p_vaddr + phdr[i].p_memsz > ALIGN_UP(phdr[i].p_vaddr + phdr[i].p_filesz, page_sz)) { 92 | void *addr = my_mmap((void *)(ALIGN_UP(base + phdr[i].p_vaddr + phdr[i].p_filesz, page_sz)), (phdr[i].p_vaddr + phdr[i].p_memsz) - ALIGN_UP(phdr[i].p_vaddr + phdr[i].p_filesz, page_sz), elf_phdr_flags_prot(phdr[i].p_flags), MAP_FIXED_NOREPLACE | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); 93 | if (addr == MAP_FAILED) { 94 | my_puts("Failed to map anonymous page!"); 95 | my_abort(); 96 | } 97 | } 98 | } else if (phdr[i].p_type == PT_GNU_STACK) { 99 | stack_prot = phdr[i].p_flags; 100 | } 101 | } 102 | 103 | /* Set the stack executable if necessary */ 104 | if (stack_prot & PF_X) { 105 | if (my_mprotect((void *)ALIGN((uintptr_t)stack, page_sz), page_sz, elf_phdr_flags_prot(stack_prot)) < 0) { 106 | my_puts("Failed to set stack permissions!"); 107 | my_abort(); 108 | } 109 | } 110 | } 111 | 112 | /* Open the executable and fetch the interpreter */ 113 | bool parse_executable(const char *executable, char *interp) { 114 | bool ret = false; 115 | 116 | /* Open the executable */ 117 | int fd = my_openat(AT_FDCWD, executable, O_RDONLY, 0); 118 | if (fd < 0) { 119 | my_puts("Failed to open executable!"); 120 | return ret; 121 | } 122 | 123 | /* Get the size of the executable */ 124 | struct stat sb; 125 | if (my_fstat(fd, &sb) < 0) { 126 | my_puts("Failed to get executable size!"); 127 | goto out_fd; 128 | } 129 | 130 | /* Map the executable into memory */ 131 | void *addr = my_mmap(NULL, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0); 132 | if (addr == MAP_FAILED) { 133 | my_puts("Failed to map executable into memory!"); 134 | goto out_fd; 135 | } 136 | 137 | /* Validate the executable as an executable */ 138 | if (!elf_ehdr_validate((const Elf_Ehdr *)addr, 1)) { 139 | my_puts("Failed to validate executable ELF header!"); 140 | goto out_mmap; 141 | } 142 | 143 | /* Get the interpreter offset */ 144 | Elf_Off interp_off = elf_phdr_interpreter((const Elf_Phdr *)((uintptr_t)addr + ((const Elf_Ehdr *)addr)->e_phoff), ((const Elf_Ehdr *)addr)->e_phnum); 145 | if (interp_off) { 146 | my_strncpy(interp, (const char *)((uintptr_t)addr + interp_off), PATH_MAX - 1); 147 | interp[PATH_MAX - 1] = '\0'; 148 | } 149 | 150 | ret = true; 151 | /* Cleanup */ 152 | out_mmap: 153 | my_munmap(addr, sb.st_size); 154 | out_fd: 155 | my_close(fd); 156 | 157 | return ret; 158 | } 159 | 160 | /* Parse the interpreter, load it into memory, and return the entry point */ 161 | void *parse_interpreter(const char *interp, void *stack, const uint8_t *rand, unsigned int page_sz) { 162 | void *ep = NULL; 163 | 164 | /* Open the interpreter */ 165 | int fd = my_openat(0, interp, O_RDONLY, 0); 166 | if (fd < 0) { 167 | my_puts("Failed to open interpreter!"); 168 | return ep; 169 | } 170 | 171 | /* Get the size of the interpreter */ 172 | struct stat sb; 173 | if (my_fstat(fd, &sb) < 0) { 174 | my_puts("Failed to get interpreter size!"); 175 | goto out_fd; 176 | } 177 | 178 | /* Map the interpreter into memory */ 179 | void *addr = my_mmap(NULL, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0); 180 | if (addr == MAP_FAILED) { 181 | my_puts("Failed to map interpreter into memory!"); 182 | goto out_fd; 183 | } 184 | 185 | /* Validate the interpreter as a library */ 186 | if (!elf_ehdr_validate((const Elf_Ehdr *)addr, 0)) { 187 | my_puts("Failed to validate interpreter ELF header!"); 188 | goto out_mmap; 189 | } 190 | 191 | /* Re-map the interpreter, at a (preferably) randomized base address, with correct permissions for each segment, and an executable stack (if necessary) */ 192 | /* Note: Cannot map everything RWX, so must map each segment individually */ 193 | unsigned long base = ALIGN(rand ? GET_RANDOM_BASE(rand) : FALLBACK_LOADER_BASE, page_sz); 194 | elf_phdr_load((const Elf_Phdr *)((uintptr_t)addr + ((const Elf_Ehdr *)addr)->e_phoff), ((const Elf_Ehdr *)addr)->e_phnum, fd, base, stack, page_sz); 195 | 196 | /* Compute the entry point */ 197 | ep = (void *)(base + ((const Elf_Ehdr *)addr)->e_entry); 198 | 199 | /* Cleanup */ 200 | out_mmap: 201 | my_munmap(addr, sb.st_size); 202 | out_fd: 203 | my_close(fd); 204 | 205 | return ep; 206 | } 207 | 208 | /* Called when executed as a dynamic loader */ 209 | void *loader_init(void *stack) { 210 | /* Parse the stack set up by the kernel's ELF executable loader */ 211 | elf_stack_parse((Elf_Addr *)stack); 212 | 213 | /* Get the page size and some random bytes */ 214 | uint8_t *rand = NULL; 215 | unsigned int page_sz = 4096; 216 | elf_auxv_parse(&page_sz, &rand); 217 | 218 | /* Open the executable and parse out the actual interpreter */ 219 | // char interp[PATH_MAX]; 220 | // if (!parse_executable(argv[0], interp)) 221 | // my_abort(); 222 | 223 | /* Open the interpreter, load it into memory, and return the entry point */ 224 | void *ep = parse_interpreter(ELF_INTERPRETER, stack, rand, page_sz); 225 | // void *ep = parse_interpreter(interp, stack, rand, page_sz); 226 | if (!ep) 227 | my_abort(); 228 | 229 | /* Enable CPUID hooking */ 230 | if (!hook_cpuid()) 231 | my_abort(); 232 | 233 | return ep; 234 | } 235 | -------------------------------------------------------------------------------- /src/loader.h: -------------------------------------------------------------------------------- 1 | #ifndef __LOADER_H__ 2 | #define __LOADER_H__ 3 | 4 | #include 5 | #include 6 | 7 | /* Architecture-specific definitions */ 8 | /* See linux/Documentation/x86/x86_64/mm.txt */ 9 | #ifdef __x86_64__ 10 | #define ELF_INTERPRETER "/lib64/ld-linux-x86-64.so.2" 11 | 12 | # define GET_RANDOM_BASE(x) ((*(uint64_t *)x) & 0x7fffffffffffUL) 13 | # define GET_ELF_MACHINE(x) ((x) == EM_X86_64) 14 | typedef Elf64_Addr Elf_Addr; 15 | typedef Elf64_Off Elf_Off; 16 | typedef Elf64_Word Elf_Word; 17 | typedef Elf64_Xword Elf_Xword; 18 | typedef Elf64_auxv_t Elf_auxv_t; 19 | typedef Elf64_Ehdr Elf_Ehdr; 20 | typedef Elf64_Phdr Elf_Phdr; 21 | #elif defined(__i386__) 22 | #define ELF_INTERPRETER "/lib/ld-linux.so.2" 23 | 24 | # define GET_RANDOM_BASE(x) ((*(uint32_t *)x) & 0xc0000000) 25 | # define GET_ELF_MACHINE(x) ((x) == EM_386 || (x) == EM_486) 26 | typedef Elf32_Addr Elf_Addr; 27 | typedef Elf32_Off Elf_Off; 28 | typedef Elf32_Word Elf_Word; 29 | typedef Elf32_Word Elf_Xword; 30 | typedef Elf32_auxv_t Elf_auxv_t; 31 | typedef Elf32_Ehdr Elf_Ehdr; 32 | typedef Elf32_Phdr Elf_Phdr; 33 | #else 34 | # error "Unsupported architecture!" 35 | #endif 36 | 37 | #define ALIGN(a, x) ((a) & ~(unsigned long)((x) - 1)) 38 | #define ALIGN_UP(a, x) ALIGN((a) + (x) - 1, (x)) 39 | 40 | /* Workaround for older non-4.17+ kernels */ 41 | #ifndef MAP_FIXED_NOREPLACE 42 | # define MAP_FIXED_NOREPLACE MAP_FIXED 43 | #endif /* MAP_FIXED_NOREPLACE */ 44 | 45 | /* Arbitrary fallback virtual address for mapping the actual interpreter */ 46 | #define FALLBACK_LOADER_BASE 0xa0000000 47 | 48 | void elf_stack_parse(Elf_Addr *stack); 49 | 50 | void elf_auxv_parse(unsigned int *page_sz, uint8_t **rand); 51 | 52 | int elf_ehdr_validate(const Elf_Ehdr *ehdr, bool exec); 53 | 54 | Elf_Off elf_phdr_interpreter(const Elf_Phdr *phdr, unsigned int num_phdr); 55 | 56 | int elf_phdr_flags_prot(Elf_Word flags); 57 | 58 | void elf_phdr_load(const Elf_Phdr *phdr, unsigned int num_phdr, int fd, unsigned long base, void *stack, unsigned int page_sz); 59 | 60 | bool parse_executable(const char *executable, char *interp); 61 | 62 | void *parse_interpreter(const char *interp, void *stack, const uint8_t *rand, unsigned int page_sz); 63 | 64 | #endif /* __LOADER_H__ */ 65 | -------------------------------------------------------------------------------- /src/syscalls.c: -------------------------------------------------------------------------------- 1 | #include 2 | #include 3 | 4 | #include "syscalls.h" 5 | 6 | int errno = 0; 7 | 8 | /* Architecture-specific definitions */ 9 | #ifdef __x86_64__ 10 | # define SA_RESTORER 0x04000000 11 | 12 | # define SYSCALL0(num) ({ unsigned long long _ret; asm volatile ("syscall\n\t" : "=a"(_ret) : "0"(num) : "memory", "cc", "r11", "cx"); (_ret); }) 13 | # define SYSCALL1(num, a1) ({ unsigned long long _ret; register __typeof__(a1) _a1 asm ("rdi") = a1; asm volatile ("syscall\n\t" : "=a"(_ret) : "0"(num), "r"(_a1) : "memory", "cc", "r11", "cx"); (_ret); }) 14 | # define SYSCALL2(num, a1, a2) ({ unsigned long long _ret; register __typeof__(a1) _a1 asm ("rdi") = a1; register __typeof__(a2) _a2 asm ("rsi") = a2; asm volatile ("syscall\n\t" : "=a"(_ret) : "0"(num), "r"(_a1), "r"(_a2) : "memory", "cc", "r11", "cx"); (_ret); }) 15 | # define SYSCALL3(num, a1, a2, a3) ({ unsigned long long _ret; register __typeof__(a1) _a1 asm ("rdi") = a1; register __typeof__(a2) _a2 asm ("rsi") = a2; register __typeof__(a3) _a3 asm ("rdx") = a3; asm volatile ("syscall\n\t" : "=a"(_ret) : "0"(num), "r"(_a1), "r"(_a2), "r"(_a3) : "memory", "cc", "r11", "cx"); (_ret); }) 16 | # define SYSCALL4(num, a1, a2, a3, a4) ({ unsigned long long _ret; register __typeof__(a1) _a1 asm ("rdi") = a1; register __typeof__(a2) _a2 asm ("rsi") = a2; register __typeof__(a3) _a3 asm ("rdx") = a3; register __typeof__(a4) _a4 asm ("r10") = a4; asm volatile ("syscall\n\t" : "=a"(_ret) : "0"(num), "r"(_a1), "r"(_a2), "r"(_a3), "r"(_a4) : "memory", "cc", "r11", "cx"); (_ret); }) 17 | # define SYSCALL5(num, a1, a2, a3, a4, a5) ({ unsigned long long _ret; register __typeof__(a1) _a1 asm ("rdi") = a1; register __typeof__(a2) _a2 asm ("rsi") = a2; register __typeof__(a3) _a3 asm ("rdx") = a3; register __typeof__(a4) _a4 asm ("r10") = a4; register __typeof__(a5) _a5 asm ("r8") = a5; asm volatile ("syscall\n\t" : "=a"(_ret) : "0"(num), "r"(_a1), "r"(_a2), "r"(_a3), "r"(_a4), "r"(_a5) : "memory", "cc", "r11", "cx"); (_ret); }) 18 | # define SYSCALL6(num, a1, a2, a3, a4, a5, a6) ({ unsigned long long _ret; register __typeof__(a1) _a1 asm ("rdi") = a1; register __typeof__(a2) _a2 asm ("rsi") = a2; register __typeof__(a3) _a3 asm ("rdx") = a3; register __typeof__(a4) _a4 asm ("r10") = a4; register __typeof__(a5) _a5 asm ("r8") = a5; register __typeof__(a6) _a6 asm ("r9") = a6; asm volatile ("syscall\n\t" : "=a"(_ret) : "0"(num), "r"(_a1), "r"(_a2), "r"(_a3), "r"(_a4), "r"(_a5), "r"(_a6) : "memory", "cc", "r11", "cx"); (_ret); }) 19 | #else 20 | # error "Unsupported architecture!" 21 | #endif 22 | 23 | #define SET_ERRNO(x) ({intptr_t r = (intptr_t)x; if (r < 0 && r > -4096) { errno = r & 4095; r = -1; } (__typeof__(x))r; }) 24 | 25 | int my_arch_prctl(int code, unsigned long addr) { 26 | return SET_ERRNO(SYSCALL2(SYS_arch_prctl, code, addr)); 27 | } 28 | 29 | int my_close(int fd) { 30 | return SET_ERRNO(SYSCALL1(SYS_close, fd)); 31 | } 32 | 33 | int my_fstat(int fd, struct stat *buf) { 34 | return SET_ERRNO(SYSCALL2(SYS_fstat, fd, buf)); 35 | } 36 | 37 | pid_t my_getpid() { 38 | return SET_ERRNO(SYSCALL0(SYS_getpid)); 39 | } 40 | 41 | pid_t my_gettid() { 42 | return SET_ERRNO(SYSCALL0(SYS_gettid)); 43 | } 44 | 45 | void *my_mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset) { 46 | return SET_ERRNO((void *)SYSCALL6(SYS_mmap, addr, length, prot, flags, fd, offset)); 47 | } 48 | 49 | int my_mprotect(void *addr, size_t len, int prot) { 50 | return SET_ERRNO(SYSCALL3(SYS_mprotect, addr, len, prot)); 51 | } 52 | 53 | int my_munmap(void *addr, size_t length) { 54 | return SET_ERRNO(SYSCALL2(SYS_munmap, addr, length)); 55 | } 56 | 57 | int my_openat(int dirfd, const char *pathname, int flags, mode_t mode) { 58 | return SET_ERRNO(SYSCALL4(SYS_openat, dirfd, pathname, flags, mode)); 59 | } 60 | 61 | int my_tgkill(int tgid, int tid, int sig) { 62 | return SET_ERRNO(SYSCALL3(SYS_tgkill, tgid, tid, sig)); 63 | } 64 | 65 | int my_rt_sigaction(int signum, const struct kernel_sigaction *act, struct kernel_sigaction *old_act, size_t set_sz) { 66 | return SET_ERRNO(SYSCALL4(SYS_rt_sigaction, signum, act, old_act, set_sz)); 67 | } 68 | 69 | ssize_t my_write(int fd, const void *buf, size_t count) { 70 | return SET_ERRNO(SYSCALL3(SYS_write, fd, buf, count)); 71 | } 72 | -------------------------------------------------------------------------------- /src/syscalls.h: -------------------------------------------------------------------------------- 1 | #ifndef __SYSCALLS_H__ 2 | #define __SYSCALLS_H__ 3 | 4 | #include 5 | #include 6 | #include 7 | 8 | #ifdef __x86_64__ 9 | struct kernel_sigaction { 10 | __sighandler_t k_sa_handler; 11 | unsigned long sa_flags; 12 | void (*sa_restorer) (void); 13 | sigset_t sa_mask; 14 | }; 15 | #else 16 | # error "Unsupported architecture!" 17 | #endif 18 | 19 | int my_arch_prctl(int code, unsigned long addr); 20 | 21 | int my_close(int fd); 22 | 23 | int my_fstat(int fd, struct stat *buf); 24 | 25 | pid_t my_getpid(); 26 | 27 | pid_t my_gettid(); 28 | 29 | void *my_mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset); 30 | 31 | int my_mprotect(void *addr, size_t len, int prot); 32 | 33 | int my_munmap(void *addr, size_t length); 34 | 35 | int my_openat(int dirfd, const char *pathname, int flags, mode_t mode); 36 | 37 | int my_tgkill(int tgid, int tid, int sig); 38 | 39 | int my_rt_sigaction(int signum, const struct kernel_sigaction *act, struct kernel_sigaction *old_act, size_t set_sz); 40 | 41 | ssize_t my_write(int fd, const void *buf, size_t count); 42 | 43 | #endif /* __SYSCALLS_H__ */ 44 | --------------------------------------------------------------------------------