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 #include <asm/mmu_context.h> 9 10 unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs) 11 { 12 unsigned long addr, seg; 13 14 addr = regs->ip; 15 seg = regs->cs & 0xffff; 16 if (v8086_mode(regs)) { 17 addr = (addr & 0xffff) + (seg << 4); 18 return addr; 19 } 20 21 /* 22 * We'll assume that the code segments in the GDT 23 * are all zero-based. That is largely true: the 24 * TLS segments are used for data, and the PNPBIOS 25 * and APM bios ones we just ignore here. 26 */ 27 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { 28 struct desc_struct *desc; 29 unsigned long base; 30 31 seg >>= 3; 32 33 mutex_lock(&child->mm->context.lock); 34 if (unlikely(!child->mm->context.ldt || 35 seg >= child->mm->context.ldt->size)) 36 addr = -1L; /* bogus selector, access would fault */ 37 else { 38 desc = &child->mm->context.ldt->entries[seg]; 39 base = get_desc_base(desc); 40 41 /* 16-bit code segment? */ 42 if (!desc->d) 43 addr &= 0xffff; 44 addr += base; 45 } 46 mutex_unlock(&child->mm->context.lock); 47 } 48 49 return addr; 50 } 51 52 static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) 53 { 54 int i, copied; 55 unsigned char opcode[15]; 56 unsigned long addr = convert_ip_to_linear(child, regs); 57 58 copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0); 59 for (i = 0; i < copied; i++) { 60 switch (opcode[i]) { 61 /* popf and iret */ 62 case 0x9d: case 0xcf: 63 return 1; 64 65 /* CHECKME: 64 65 */ 66 67 /* opcode and address size prefixes */ 68 case 0x66: case 0x67: 69 continue; 70 /* irrelevant prefixes (segment overrides and repeats) */ 71 case 0x26: case 0x2e: 72 case 0x36: case 0x3e: 73 case 0x64: case 0x65: 74 case 0xf0: case 0xf2: case 0xf3: 75 continue; 76 77 #ifdef CONFIG_X86_64 78 case 0x40 ... 0x4f: 79 if (!user_64bit_mode(regs)) 80 /* 32-bit mode: register increment */ 81 return 0; 82 /* 64-bit mode: REX prefix */ 83 continue; 84 #endif 85 86 /* CHECKME: f2, f3 */ 87 88 /* 89 * pushf: NOTE! We should probably not let 90 * the user see the TF bit being set. But 91 * it's more pain than it's worth to avoid 92 * it, and a debugger could emulate this 93 * all in user space if it _really_ cares. 94 */ 95 case 0x9c: 96 default: 97 return 0; 98 } 99 } 100 return 0; 101 } 102 103 /* 104 * Enable single-stepping. Return nonzero if user mode is not using TF itself. 105 */ 106 static int enable_single_step(struct task_struct *child) 107 { 108 struct pt_regs *regs = task_pt_regs(child); 109 unsigned long oflags; 110 111 /* 112 * If we stepped into a sysenter/syscall insn, it trapped in 113 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. 114 * If user-mode had set TF itself, then it's still clear from 115 * do_debug() and we need to set it again to restore the user 116 * state so we don't wrongly set TIF_FORCED_TF below. 117 * If enable_single_step() was used last and that is what 118 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are 119 * already set and our bookkeeping is fine. 120 */ 121 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP))) 122 regs->flags |= X86_EFLAGS_TF; 123 124 /* 125 * Always set TIF_SINGLESTEP - this guarantees that 126 * we single-step system calls etc.. This will also 127 * cause us to set TF when returning to user mode. 128 */ 129 set_tsk_thread_flag(child, TIF_SINGLESTEP); 130 131 oflags = regs->flags; 132 133 /* Set TF on the kernel stack.. */ 134 regs->flags |= X86_EFLAGS_TF; 135 136 /* 137 * ..but if TF is changed by the instruction we will trace, 138 * don't mark it as being "us" that set it, so that we 139 * won't clear it by hand later. 140 * 141 * Note that if we don't actually execute the popf because 142 * of a signal arriving right now or suchlike, we will lose 143 * track of the fact that it really was "us" that set it. 144 */ 145 if (is_setting_trap_flag(child, regs)) { 146 clear_tsk_thread_flag(child, TIF_FORCED_TF); 147 return 0; 148 } 149 150 /* 151 * If TF was already set, check whether it was us who set it. 152 * If not, we should never attempt a block step. 153 */ 154 if (oflags & X86_EFLAGS_TF) 155 return test_tsk_thread_flag(child, TIF_FORCED_TF); 156 157 set_tsk_thread_flag(child, TIF_FORCED_TF); 158 159 return 1; 160 } 161 162 void set_task_blockstep(struct task_struct *task, bool on) 163 { 164 unsigned long debugctl; 165 166 /* 167 * Ensure irq/preemption can't change debugctl in between. 168 * Note also that both TIF_BLOCKSTEP and debugctl should 169 * be changed atomically wrt preemption. 170 * 171 * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if 172 * task is current or it can't be running, otherwise we can race 173 * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but 174 * PTRACE_KILL is not safe. 175 */ 176 local_irq_disable(); 177 debugctl = get_debugctlmsr(); 178 if (on) { 179 debugctl |= DEBUGCTLMSR_BTF; 180 set_tsk_thread_flag(task, TIF_BLOCKSTEP); 181 } else { 182 debugctl &= ~DEBUGCTLMSR_BTF; 183 clear_tsk_thread_flag(task, TIF_BLOCKSTEP); 184 } 185 if (task == current) 186 update_debugctlmsr(debugctl); 187 local_irq_enable(); 188 } 189 190 /* 191 * Enable single or block step. 192 */ 193 static void enable_step(struct task_struct *child, bool block) 194 { 195 /* 196 * Make sure block stepping (BTF) is not enabled unless it should be. 197 * Note that we don't try to worry about any is_setting_trap_flag() 198 * instructions after the first when using block stepping. 199 * So no one should try to use debugger block stepping in a program 200 * that uses user-mode single stepping itself. 201 */ 202 if (enable_single_step(child) && block) 203 set_task_blockstep(child, true); 204 else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) 205 set_task_blockstep(child, false); 206 } 207 208 void user_enable_single_step(struct task_struct *child) 209 { 210 enable_step(child, 0); 211 } 212 213 void user_enable_block_step(struct task_struct *child) 214 { 215 enable_step(child, 1); 216 } 217 218 void user_disable_single_step(struct task_struct *child) 219 { 220 /* 221 * Make sure block stepping (BTF) is disabled. 222 */ 223 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) 224 set_task_blockstep(child, false); 225 226 /* Always clear TIF_SINGLESTEP... */ 227 clear_tsk_thread_flag(child, TIF_SINGLESTEP); 228 229 /* But touch TF only if it was set by us.. */ 230 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF)) 231 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; 232 } 233