2 * x86 single-step support code, common to 32-bit and 64-bit.
4 #include <linux/sched.h>
6 #include <linux/ptrace.h>
8 #include <asm/mmu_context.h>
10 unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
12 unsigned long addr, seg;
15 seg = regs->cs & 0xffff;
16 if (v8086_mode(regs)) {
17 addr = (addr & 0xffff) + (seg << 4);
21 #ifdef CONFIG_MODIFY_LDT_SYSCALL
23 * We'll assume that the code segments in the GDT
24 * are all zero-based. That is largely true: the
25 * TLS segments are used for data, and the PNPBIOS
26 * and APM bios ones we just ignore here.
28 if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
29 struct desc_struct *desc;
34 mutex_lock(&child->mm->context.lock);
35 if (unlikely(!child->mm->context.ldt ||
36 seg >= child->mm->context.ldt->size))
37 addr = -1L; /* bogus selector, access would fault */
39 desc = &child->mm->context.ldt->entries[seg];
40 base = get_desc_base(desc);
42 /* 16-bit code segment? */
47 mutex_unlock(&child->mm->context.lock);
54 static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
57 unsigned char opcode[15];
58 unsigned long addr = convert_ip_to_linear(child, regs);
60 copied = access_process_vm(child, addr, opcode, sizeof(opcode),
62 for (i = 0; i < copied; i++) {
70 /* opcode and address size prefixes */
73 /* irrelevant prefixes (segment overrides and repeats) */
77 case 0xf0: case 0xf2: case 0xf3:
82 if (!user_64bit_mode(regs))
83 /* 32-bit mode: register increment */
85 /* 64-bit mode: REX prefix */
92 * pushf: NOTE! We should probably not let
93 * the user see the TF bit being set. But
94 * it's more pain than it's worth to avoid
95 * it, and a debugger could emulate this
96 * all in user space if it _really_ cares.
107 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
109 static int enable_single_step(struct task_struct *child)
111 struct pt_regs *regs = task_pt_regs(child);
112 unsigned long oflags;
115 * If we stepped into a sysenter/syscall insn, it trapped in
116 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
117 * If user-mode had set TF itself, then it's still clear from
118 * do_debug() and we need to set it again to restore the user
119 * state so we don't wrongly set TIF_FORCED_TF below.
120 * If enable_single_step() was used last and that is what
121 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
122 * already set and our bookkeeping is fine.
124 if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
125 regs->flags |= X86_EFLAGS_TF;
128 * Always set TIF_SINGLESTEP - this guarantees that
129 * we single-step system calls etc.. This will also
130 * cause us to set TF when returning to user mode.
132 set_tsk_thread_flag(child, TIF_SINGLESTEP);
134 oflags = regs->flags;
136 /* Set TF on the kernel stack.. */
137 regs->flags |= X86_EFLAGS_TF;
140 * ..but if TF is changed by the instruction we will trace,
141 * don't mark it as being "us" that set it, so that we
142 * won't clear it by hand later.
144 * Note that if we don't actually execute the popf because
145 * of a signal arriving right now or suchlike, we will lose
146 * track of the fact that it really was "us" that set it.
148 if (is_setting_trap_flag(child, regs)) {
149 clear_tsk_thread_flag(child, TIF_FORCED_TF);
154 * If TF was already set, check whether it was us who set it.
155 * If not, we should never attempt a block step.
157 if (oflags & X86_EFLAGS_TF)
158 return test_tsk_thread_flag(child, TIF_FORCED_TF);
160 set_tsk_thread_flag(child, TIF_FORCED_TF);
165 void set_task_blockstep(struct task_struct *task, bool on)
167 unsigned long debugctl;
170 * Ensure irq/preemption can't change debugctl in between.
171 * Note also that both TIF_BLOCKSTEP and debugctl should
172 * be changed atomically wrt preemption.
174 * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if
175 * task is current or it can't be running, otherwise we can race
176 * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but
177 * PTRACE_KILL is not safe.
180 debugctl = get_debugctlmsr();
182 debugctl |= DEBUGCTLMSR_BTF;
183 set_tsk_thread_flag(task, TIF_BLOCKSTEP);
185 debugctl &= ~DEBUGCTLMSR_BTF;
186 clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
189 update_debugctlmsr(debugctl);
194 * Enable single or block step.
196 static void enable_step(struct task_struct *child, bool block)
199 * Make sure block stepping (BTF) is not enabled unless it should be.
200 * Note that we don't try to worry about any is_setting_trap_flag()
201 * instructions after the first when using block stepping.
202 * So no one should try to use debugger block stepping in a program
203 * that uses user-mode single stepping itself.
205 if (enable_single_step(child) && block)
206 set_task_blockstep(child, true);
207 else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
208 set_task_blockstep(child, false);
211 void user_enable_single_step(struct task_struct *child)
213 enable_step(child, 0);
216 void user_enable_block_step(struct task_struct *child)
218 enable_step(child, 1);
221 void user_disable_single_step(struct task_struct *child)
224 * Make sure block stepping (BTF) is disabled.
226 if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
227 set_task_blockstep(child, false);
229 /* Always clear TIF_SINGLESTEP... */
230 clear_tsk_thread_flag(child, TIF_SINGLESTEP);
232 /* But touch TF only if it was set by us.. */
233 if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
234 task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;