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 #include <asm/desc.h> 8 9 unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs) 10 { 11 unsigned long addr, seg; 12 13 addr = regs->ip; 14 seg = regs->cs & 0xffff; 15 if (v8086_mode(regs)) { 16 addr = (addr & 0xffff) + (seg << 4); 17 return addr; 18 } 19 20 /* 21 * We'll assume that the code segments in the GDT 22 * are all zero-based. That is largely true: the 23 * TLS segments are used for data, and the PNPBIOS 24 * and APM bios ones we just ignore here. 25 */ 26 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { 27 struct desc_struct *desc; 28 unsigned long base; 29 30 seg &= ~7UL; 31 32 mutex_lock(&child->mm->context.lock); 33 if (unlikely((seg >> 3) >= child->mm->context.size)) 34 addr = -1L; /* bogus selector, access would fault */ 35 else { 36 desc = child->mm->context.ldt + seg; 37 base = get_desc_base(desc); 38 39 /* 16-bit code segment? */ 40 if (!desc->d) 41 addr &= 0xffff; 42 addr += base; 43 } 44 mutex_unlock(&child->mm->context.lock); 45 } 46 47 return addr; 48 } 49 50 static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) 51 { 52 int i, copied; 53 unsigned char opcode[15]; 54 unsigned long addr = convert_ip_to_linear(child, regs); 55 56 copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0); 57 for (i = 0; i < copied; i++) { 58 switch (opcode[i]) { 59 /* popf and iret */ 60 case 0x9d: case 0xcf: 61 return 1; 62 63 /* CHECKME: 64 65 */ 64 65 /* opcode and address size prefixes */ 66 case 0x66: case 0x67: 67 continue; 68 /* irrelevant prefixes (segment overrides and repeats) */ 69 case 0x26: case 0x2e: 70 case 0x36: case 0x3e: 71 case 0x64: case 0x65: 72 case 0xf0: case 0xf2: case 0xf3: 73 continue; 74 75 #ifdef CONFIG_X86_64 76 case 0x40 ... 0x4f: 77 if (!user_64bit_mode(regs)) 78 /* 32-bit mode: register increment */ 79 return 0; 80 /* 64-bit mode: REX prefix */ 81 continue; 82 #endif 83 84 /* CHECKME: f2, f3 */ 85 86 /* 87 * pushf: NOTE! We should probably not let 88 * the user see the TF bit being set. But 89 * it's more pain than it's worth to avoid 90 * it, and a debugger could emulate this 91 * all in user space if it _really_ cares. 92 */ 93 case 0x9c: 94 default: 95 return 0; 96 } 97 } 98 return 0; 99 } 100 101 /* 102 * Enable single-stepping. Return nonzero if user mode is not using TF itself. 103 */ 104 static int enable_single_step(struct task_struct *child) 105 { 106 struct pt_regs *regs = task_pt_regs(child); 107 unsigned long oflags; 108 109 /* 110 * If we stepped into a sysenter/syscall insn, it trapped in 111 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. 112 * If user-mode had set TF itself, then it's still clear from 113 * do_debug() and we need to set it again to restore the user 114 * state so we don't wrongly set TIF_FORCED_TF below. 115 * If enable_single_step() was used last and that is what 116 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are 117 * already set and our bookkeeping is fine. 118 */ 119 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP))) 120 regs->flags |= X86_EFLAGS_TF; 121 122 /* 123 * Always set TIF_SINGLESTEP - this guarantees that 124 * we single-step system calls etc.. This will also 125 * cause us to set TF when returning to user mode. 126 */ 127 set_tsk_thread_flag(child, TIF_SINGLESTEP); 128 129 oflags = regs->flags; 130 131 /* Set TF on the kernel stack.. */ 132 regs->flags |= X86_EFLAGS_TF; 133 134 /* 135 * ..but if TF is changed by the instruction we will trace, 136 * don't mark it as being "us" that set it, so that we 137 * won't clear it by hand later. 138 * 139 * Note that if we don't actually execute the popf because 140 * of a signal arriving right now or suchlike, we will lose 141 * track of the fact that it really was "us" that set it. 142 */ 143 if (is_setting_trap_flag(child, regs)) { 144 clear_tsk_thread_flag(child, TIF_FORCED_TF); 145 return 0; 146 } 147 148 /* 149 * If TF was already set, check whether it was us who set it. 150 * If not, we should never attempt a block step. 151 */ 152 if (oflags & X86_EFLAGS_TF) 153 return test_tsk_thread_flag(child, TIF_FORCED_TF); 154 155 set_tsk_thread_flag(child, TIF_FORCED_TF); 156 157 return 1; 158 } 159 160 void set_task_blockstep(struct task_struct *task, bool on) 161 { 162 unsigned long debugctl; 163 164 /* 165 * Ensure irq/preemption can't change debugctl in between. 166 * Note also that both TIF_BLOCKSTEP and debugctl should 167 * be changed atomically wrt preemption. 168 * 169 * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if 170 * task is current or it can't be running, otherwise we can race 171 * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but 172 * PTRACE_KILL is not safe. 173 */ 174 local_irq_disable(); 175 debugctl = get_debugctlmsr(); 176 if (on) { 177 debugctl |= DEBUGCTLMSR_BTF; 178 set_tsk_thread_flag(task, TIF_BLOCKSTEP); 179 } else { 180 debugctl &= ~DEBUGCTLMSR_BTF; 181 clear_tsk_thread_flag(task, TIF_BLOCKSTEP); 182 } 183 if (task == current) 184 update_debugctlmsr(debugctl); 185 local_irq_enable(); 186 } 187 188 /* 189 * Enable single or block step. 190 */ 191 static void enable_step(struct task_struct *child, bool block) 192 { 193 /* 194 * Make sure block stepping (BTF) is not enabled unless it should be. 195 * Note that we don't try to worry about any is_setting_trap_flag() 196 * instructions after the first when using block stepping. 197 * So no one should try to use debugger block stepping in a program 198 * that uses user-mode single stepping itself. 199 */ 200 if (enable_single_step(child) && block) 201 set_task_blockstep(child, true); 202 else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) 203 set_task_blockstep(child, false); 204 } 205 206 void user_enable_single_step(struct task_struct *child) 207 { 208 enable_step(child, 0); 209 } 210 211 void user_enable_block_step(struct task_struct *child) 212 { 213 enable_step(child, 1); 214 } 215 216 void user_disable_single_step(struct task_struct *child) 217 { 218 /* 219 * Make sure block stepping (BTF) is disabled. 220 */ 221 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) 222 set_task_blockstep(child, false); 223 224 /* Always clear TIF_SINGLESTEP... */ 225 clear_tsk_thread_flag(child, TIF_SINGLESTEP); 226 227 /* But touch TF only if it was set by us.. */ 228 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF)) 229 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; 230 } 231