1// SPDX-License-Identifier: GPL-2.0 2/* 3 * x86 single-step support code, common to 32-bit and 64-bit. 4 */ 5#include <linux/sched.h> 6#include <linux/sched/task_stack.h> 7#include <linux/mm.h> 8#include <linux/ptrace.h> 9#include <asm/desc.h> 10#include <asm/mmu_context.h> 11 12unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs) 13{ 14 unsigned long addr, seg; 15 16 addr = regs->ip; 17 seg = regs->cs; 18 if (v8086_mode(regs)) { 19 addr = (addr & 0xffff) + (seg << 4); 20 return addr; 21 } 22 23#ifdef CONFIG_MODIFY_LDT_SYSCALL 24 /* 25 * We'll assume that the code segments in the GDT 26 * are all zero-based. That is largely true: the 27 * TLS segments are used for data, and the PNPBIOS 28 * and APM bios ones we just ignore here. 29 */ 30 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { 31 struct desc_struct *desc; 32 unsigned long base; 33 34 seg >>= 3; 35 36 mutex_lock(&child->mm->context.lock); 37 if (unlikely(!child->mm->context.ldt || 38 seg >= child->mm->context.ldt->nr_entries)) 39 addr = -1L; /* bogus selector, access would fault */ 40 else { 41 desc = &child->mm->context.ldt->entries[seg]; 42 base = get_desc_base(desc); 43 44 /* 16-bit code segment? */ 45 if (!desc->d) 46 addr &= 0xffff; 47 addr += base; 48 } 49 mutex_unlock(&child->mm->context.lock); 50 } 51#endif 52 53 return addr; 54} 55 56static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) 57{ 58 int i, copied; 59 unsigned char opcode[15]; 60 unsigned long addr = convert_ip_to_linear(child, regs); 61 62 copied = access_process_vm(child, addr, opcode, sizeof(opcode), 63 FOLL_FORCE); 64 for (i = 0; i < copied; i++) { 65 switch (opcode[i]) { 66 /* popf and iret */ 67 case 0x9d: case 0xcf: 68 return 1; 69 70 /* CHECKME: 64 65 */ 71 72 /* opcode and address size prefixes */ 73 case 0x66: case 0x67: 74 continue; 75 /* irrelevant prefixes (segment overrides and repeats) */ 76 case 0x26: case 0x2e: 77 case 0x36: case 0x3e: 78 case 0x64: case 0x65: 79 case 0xf0: case 0xf2: case 0xf3: 80 continue; 81 82#ifdef CONFIG_X86_64 83 case 0x40 ... 0x4f: 84 if (!user_64bit_mode(regs)) 85 /* 32-bit mode: register increment */ 86 return 0; 87 /* 64-bit mode: REX prefix */ 88 continue; 89#endif 90 91 /* CHECKME: f2, f3 */ 92 93 /* 94 * pushf: NOTE! We should probably not let 95 * the user see the TF bit being set. But 96 * it's more pain than it's worth to avoid 97 * it, and a debugger could emulate this 98 * all in user space if it _really_ cares. 99 */ 100 case 0x9c: 101 default: 102 return 0; 103 } 104 } 105 return 0; 106} 107 108/* 109 * Enable single-stepping. Return nonzero if user mode is not using TF itself. 110 */ 111static int enable_single_step(struct task_struct *child) 112{ 113 struct pt_regs *regs = task_pt_regs(child); 114 unsigned long oflags; 115 116 /* 117 * If we stepped into a sysenter/syscall insn, it trapped in 118 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. 119 * If user-mode had set TF itself, then it's still clear from 120 * do_debug() and we need to set it again to restore the user 121 * state so we don't wrongly set TIF_FORCED_TF below. 122 * If enable_single_step() was used last and that is what 123 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are 124 * already set and our bookkeeping is fine. 125 */ 126 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP))) 127 regs->flags |= X86_EFLAGS_TF; 128 129 /* 130 * Always set TIF_SINGLESTEP. This will also 131 * cause us to set TF when returning to user mode. 132 */ 133 set_tsk_thread_flag(child, TIF_SINGLESTEP); 134 135 /* 136 * Ensure that a trap is triggered once stepping out of a system 137 * call prior to executing any user instruction. 138 */ 139 set_task_syscall_work(child, SYSCALL_EXIT_TRAP); 140 141 oflags = regs->flags; 142 143 /* Set TF on the kernel stack.. */ 144 regs->flags |= X86_EFLAGS_TF; 145 146 /* 147 * ..but if TF is changed by the instruction we will trace, 148 * don't mark it as being "us" that set it, so that we 149 * won't clear it by hand later. 150 * 151 * Note that if we don't actually execute the popf because 152 * of a signal arriving right now or suchlike, we will lose 153 * track of the fact that it really was "us" that set it. 154 */ 155 if (is_setting_trap_flag(child, regs)) { 156 clear_tsk_thread_flag(child, TIF_FORCED_TF); 157 return 0; 158 } 159 160 /* 161 * If TF was already set, check whether it was us who set it. 162 * If not, we should never attempt a block step. 163 */ 164 if (oflags & X86_EFLAGS_TF) 165 return test_tsk_thread_flag(child, TIF_FORCED_TF); 166 167 set_tsk_thread_flag(child, TIF_FORCED_TF); 168 169 return 1; 170} 171 172void set_task_blockstep(struct task_struct *task, bool on) 173{ 174 unsigned long debugctl; 175 176 /* 177 * Ensure irq/preemption can't change debugctl in between. 178 * Note also that both TIF_BLOCKSTEP and debugctl should 179 * be changed atomically wrt preemption. 180 * 181 * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if 182 * task is current or it can't be running, otherwise we can race 183 * with __switch_to_xtra(). We rely on ptrace_freeze_traced(). 184 */ 185 local_irq_disable(); 186 debugctl = get_debugctlmsr(); 187 if (on) { 188 debugctl |= DEBUGCTLMSR_BTF; 189 set_tsk_thread_flag(task, TIF_BLOCKSTEP); 190 } else { 191 debugctl &= ~DEBUGCTLMSR_BTF; 192 clear_tsk_thread_flag(task, TIF_BLOCKSTEP); 193 } 194 if (task == current) 195 update_debugctlmsr(debugctl); 196 local_irq_enable(); 197} 198 199/* 200 * Enable single or block step. 201 */ 202static void enable_step(struct task_struct *child, bool block) 203{ 204 /* 205 * Make sure block stepping (BTF) is not enabled unless it should be. 206 * Note that we don't try to worry about any is_setting_trap_flag() 207 * instructions after the first when using block stepping. 208 * So no one should try to use debugger block stepping in a program 209 * that uses user-mode single stepping itself. 210 */ 211 if (enable_single_step(child) && block) 212 set_task_blockstep(child, true); 213 else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) 214 set_task_blockstep(child, false); 215} 216 217void user_enable_single_step(struct task_struct *child) 218{ 219 enable_step(child, 0); 220} 221 222void user_enable_block_step(struct task_struct *child) 223{ 224 enable_step(child, 1); 225} 226 227void user_disable_single_step(struct task_struct *child) 228{ 229 /* 230 * Make sure block stepping (BTF) is disabled. 231 */ 232 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) 233 set_task_blockstep(child, false); 234 235 /* Always clear TIF_SINGLESTEP... */ 236 clear_tsk_thread_flag(child, TIF_SINGLESTEP); 237 clear_task_syscall_work(child, SYSCALL_EXIT_TRAP); 238 239 /* But touch TF only if it was set by us.. */ 240 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF)) 241 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF; 242} 243