/* * Copyright 2002-2019 Intel Corporation. * * This software is provided to you as Sample Source Code as defined in the accompanying * End User License Agreement for the Intel(R) Software Development Products ("Agreement") * section 1.L. * * This software and the related documents are provided as is, with no express or implied * warranties, other than those that are expressly stated in the License. */ #include #include #include #include #include #include #include #include #include #include #define NTHREADS 4 typedef struct { unsigned int entry_number; unsigned int base_addr; unsigned int limit; unsigned int seg_32bit:1; unsigned int contents:2; unsigned int read_exec_only:1; unsigned int limit_in_pages:1; unsigned int seg_not_present:1; unsigned int useable:1; }UserDesc; # define TLS_GET_GS_REG() \ ({ int __seg; __asm ("movw %%gs, %w0" : "=q" (__seg)); __seg & 0xffff; }) # define TLS_SET_GS_REG(val) \ __asm ("movw %w0, %%gs" :: "q" (val)) #define LDT_GET 0 #define LDT_SET 1 #define FILL_ENTRIES 10 struct LDT_TABLE_ENTRY { LDT_TABLE_ENTRY(): _val1(0), _val2(0) {} unsigned int _val1; unsigned int _val2; }; inline unsigned int LDTEntryA(unsigned int base) { return base << 16; } char buf[NTHREADS][3000]; void * thread_func (void *arg) { unsigned long thread_no = (unsigned long)arg+1; unsigned int gs_value = TLS_GET_GS_REG(); sprintf(buf[thread_no-1],"gs value for thread %ld is 0x%x\n", thread_no, gs_value ); LDT_TABLE_ENTRY ldtEntries[FILL_ENTRIES]; unsigned int sizeInBytes = sizeof(LDT_TABLE_ENTRY)*FILL_ENTRIES; int res = syscall(SYS_modify_ldt, LDT_GET, ldtEntries, sizeInBytes); if (res != sizeInBytes) { printf("LDT_GET failed\n"); return 0; } if (((gs_value >> 2)& 1) == 0) { sprintf(buf[thread_no-1],"%sGS points to GDT\n", buf[thread_no-1]); for (unsigned int i=0; i> 3; if (LDTEntryA(entry) == ldtEntries[entry]._val1) { sprintf(buf[thread_no-1],"%sThread %d: original LDT entry %d\n", buf[thread_no-1], thread_no, entry); } else { sprintf(buf[thread_no-1],"%sThread %d: modified LDT entry %d\n", buf[thread_no-1], thread_no, entry); } } return 0; } int main (int argc, char *argv[]) { pthread_t h[NTHREADS]; UserDesc tr[FILL_ENTRIES]; int res; memset(tr, 0, sizeof(UserDesc)*FILL_ENTRIES); unsigned long num = pthread_self(); for (unsigned int i = 1; i < FILL_ENTRIES; i++) { tr[i].entry_number = i; tr[i].base_addr = i; res = syscall(SYS_modify_ldt, LDT_SET, &tr[i], sizeof(UserDesc)); if (res < 0) { printf("main thread: LDT_GET for entry %d failed, code %d, %s\n", i, errno, strerror(errno) ); } } LDT_TABLE_ENTRY ldtEntries[FILL_ENTRIES]; unsigned int sizeInBytes = sizeof(LDT_TABLE_ENTRY)*FILL_ENTRIES; res = syscall(SYS_modify_ldt, LDT_GET, ldtEntries, sizeInBytes); if (res != sizeInBytes) { printf("LDT_GET failed\n"); return 0; } for (unsigned int i = 1; i < FILL_ENTRIES; i++) { printf("ldt entry %d 0x%x \n", i, ldtEntries[i]._val1); } printf("Original GS for the main thread is 0x%x\n", TLS_GET_GS_REG() ); for (unsigned long i = 0; i < NTHREADS; i++) { pthread_create (&h[i], 0, thread_func, (void *)i); } for (unsigned long i = 0; i < NTHREADS; i++) { pthread_join (h[i], 0); } for (unsigned long i = 0; i < NTHREADS; i++) { printf("%s", buf[i]); } }