1 /* 2 * x86 single-step support code, common to 32-bit and 64-bit. 3 */ 4 #include <linux/sched.h> 5 #include <linux/mm.h> 6 #include <linux/ptrace.h> 7 8 unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs) 9 { 10 unsigned long addr, seg; 11 12 addr = regs->ip; 13 seg = regs->cs & 0xffff; 14 if (v8086_mode(regs)) { 15 addr = (addr & 0xffff) + (seg << 4); 16 return addr; 17 } 18 19 /* 20 * We'll assume that the code segments in the GDT 21 * are all zero-based. That is largely true: the 22 * TLS segments are used for data, and the PNPBIOS 23 * and APM bios ones we just ignore here. 24 */ 25 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { 26 u32 *desc; 27 unsigned long base; 28 29 seg &= ~7UL; 30 31 mutex_lock(&child->mm->context.lock); 32 if (unlikely((seg >> 3) >= child->mm->context.size)) 33 addr = -1L; /* bogus selector, access would fault */ 34 else { 35 desc = child->mm->context.ldt + seg; 36 base = ((desc[0] >> 16) | 37 ((desc[1] & 0xff) << 16) | 38 (desc[1] & 0xff000000)); 39 40 /* 16-bit code segment? */ 41 if (!((desc[1] >> 22) & 1)) 42 addr &= 0xffff; 43 addr += base; 44 } 45 mutex_unlock(&child->mm->context.lock); 46 } 47 48 return addr; 49 } 50 51 static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) 52 { 53 int i, copied; 54 unsigned char opcode[15]; 55 unsigned long addr = convert_ip_to_linear(child, regs); 56 57 copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0); 58 for (i = 0; i < copied; i++) { 59 switch (opcode[i]) { 60 /* popf and iret */ 61 case 0x9d: case 0xcf: 62 return 1; 63 64 /* CHECKME: 64 65 */ 65 66 /* opcode and address size prefixes */ 67 case 0x66: case 0x67: 68 continue; 69 /* irrelevant prefixes (segment overrides and repeats) */ 70 case 0x26: case 0x2e: 71 case 0x36: case 0x3e: 72 case 0x64: case 0x65: 73 case 0xf0: case 0xf2: case 0xf3: 74 continue; 75 76 #ifdef CONFIG_X86_64 77 case 0x40 ... 0x4f: 78 if (regs->cs != __USER_CS) 79 /* 32-bit mode: register increment */ 80 return 0; 81 /* 64-bit mode: REX prefix */ 82 continue; 83 #endif 84 85 /* CHECKME: f2, f3 */ 86 87 /* 88 * pushf: NOTE! We should probably not let 89 * the user see the TF bit being set. But 90 * it's more pain than it's worth to avoid 91 * it, and a debugger could emulate this 92 * all in user space if it _really_ cares. 93 */ 94 case 0x9c: 95 default: 96 return 0; 97 } 98 } 99 return 0; 100 } 101 102 /* 103 * Enable single-stepping. Return nonzero if user mode is not using TF itself. 104 */ 105 static int enable_single_step(struct task_struct *child) 106 { 107 struct pt_regs *regs = task_pt_regs(child); 108 unsigned long oflags; 109 110 /* 111 * If we stepped into a sysenter/syscall insn, it trapped in 112 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. 113 * If user-mode had set TF itself, then it's still clear from 114 * do_debug() and we need to set it again to restore the user 115 * state so we don't wrongly set TIF_FORCED_TF below. 116 * If enable_single_step() was used last and that is what 117 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are 118 * already set and our bookkeeping is fine. 119 */ 120 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP))) 121 regs->flags |= X86_EFLAGS_TF; 122 123 /* 124 * Always set TIF_SINGLESTEP - this guarantees that 125 * we single-step system calls etc.. This will also 126 * cause us to set TF when returning to user mode. 127 */ 128 set_tsk_thread_flag(child, TIF_SINGLESTEP); 129 130 oflags = regs->flags; 131 132 /* Set TF on the kernel stack.. */ 133 regs->flags |= X86_EFLAGS_TF; 134 135 /* 136 * ..but if TF is changed by the instruction we will trace, 137 * don't mark it as being "us" that set it, so that we 138 * won't clear it by hand later. 139 * 140 * Note that if we don't actually execute the popf because 141 * of a signal arriving right now or suchlike, we will lose 142 * track of the fact that it really was "us" that set it. 143 */ 144 if (is_setting_trap_flag(child, regs)) { 145 clear_tsk_thread_flag(child, TIF_FORCED_TF); 146 return 0; 147 } 148 149 /* 150 * If TF was already set, check whether it was us who set it. 151 * If not, we should never attempt a block step. 152 */ 153 if (oflags & X86_EFLAGS_TF) 154 return test_tsk_thread_flag(child, TIF_FORCED_TF); 155 156 set_tsk_thread_flag(child, TIF_FORCED_TF); 157 158 return 1; 159 } 160 161 /* 162 * Install this value in MSR_IA32_DEBUGCTLMSR whenever child is running. 163 */ 164 static void write_debugctlmsr(struct task_struct *child, unsigned long val) 165 { 166 if (child->thread.debugctlmsr == val) 167 return; 168 169 child->thread.debugctlmsr = val; 170 171 if (child != current) 172 return; 173 174 update_debugctlmsr(val); 175 } 176 177 /* 178 * Enable single or block step. 179 */ 180 static void enable_step(struct task_struct *child, bool block) 181 { 182 /* 183 * Make sure block stepping (BTF) is not enabled unless it should be. 184 * Note that we don't try to worry about any is_setting_trap_flag() 185 * instructions after the first when using block stepping. 186 * So noone should try to use debugger block stepping in a program 187 * that uses user-mode single stepping itself. 188 */ 189 if (enable_single_step(child) && block) { 190 set_tsk_thread_flag(child, TIF_DEBUGCTLMSR); 191 write_debugctlmsr(child, 192 child->thread.debugctlmsr | DEBUGCTLMSR_BTF); 193 } else { 194 write_debugctlmsr(child, 195 child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF); 196 197 if (!child->thread.debugctlmsr) 198 clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR); 199 } 200 } 201 202 void user_enable_single_step(struct task_struct *child) 203 { 204 enable_step(child, 0); 205 } 206 207 void user_enable_block_step(struct task_struct *child) 208 { 209 enable_step(child, 1); 210 } 211 212 void user_disable_single_step(struct task_struct *child) 213 { 214 /* 215 * Make sure block stepping (BTF) is disabled. 216 */ 217 write_debugctlmsr(child, 218 child->thread.debugctlmsr & ~DEBUGCTLMSR_BTF); 219 220 if (!child->thread.debugctlmsr) 221 clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR); 222 223 /* Always clear TIF_SINGLESTEP... */ 224 clear_tsk_thread_flag(child, TIF_SINGLESTEP); 225 226 /* But touch TF only if it was set by us.. */ 227 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF)) 228 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; 229 } 230