]>
git.proxmox.com Git - mirror_ubuntu-artful-kernel.git/blob - arch/x86/kernel/step.c
2 * x86 single-step support code, common to 32-bit and 64-bit.
4 #include <linux/sched.h>
6 #include <linux/ptrace.h>
9 unsigned long convert_ip_to_linear(struct task_struct
*child
, struct pt_regs
*regs
)
11 unsigned long addr
, seg
;
14 seg
= regs
->cs
& 0xffff;
15 if (v8086_mode(regs
)) {
16 addr
= (addr
& 0xffff) + (seg
<< 4);
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.
26 if ((seg
& SEGMENT_TI_MASK
) == SEGMENT_LDT
) {
27 struct desc_struct
*desc
;
32 mutex_lock(&child
->mm
->context
.lock
);
33 if (unlikely((seg
>> 3) >= child
->mm
->context
.size
))
34 addr
= -1L; /* bogus selector, access would fault */
36 desc
= child
->mm
->context
.ldt
+ seg
;
37 base
= get_desc_base(desc
);
39 /* 16-bit code segment? */
44 mutex_unlock(&child
->mm
->context
.lock
);
50 static int is_setting_trap_flag(struct task_struct
*child
, struct pt_regs
*regs
)
53 unsigned char opcode
[15];
54 unsigned long addr
= convert_ip_to_linear(child
, regs
);
56 copied
= access_process_vm(child
, addr
, opcode
, sizeof(opcode
), 0);
57 for (i
= 0; i
< copied
; i
++) {
65 /* opcode and address size prefixes */
68 /* irrelevant prefixes (segment overrides and repeats) */
72 case 0xf0: case 0xf2: case 0xf3:
77 if (!user_64bit_mode(regs
))
78 /* 32-bit mode: register increment */
80 /* 64-bit mode: REX prefix */
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.
102 * Enable single-stepping. Return nonzero if user mode is not using TF itself.
104 static int enable_single_step(struct task_struct
*child
)
106 struct pt_regs
*regs
= task_pt_regs(child
);
107 unsigned long oflags
;
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.
119 if (unlikely(test_tsk_thread_flag(child
, TIF_SINGLESTEP
)))
120 regs
->flags
|= X86_EFLAGS_TF
;
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.
127 set_tsk_thread_flag(child
, TIF_SINGLESTEP
);
129 oflags
= regs
->flags
;
131 /* Set TF on the kernel stack.. */
132 regs
->flags
|= X86_EFLAGS_TF
;
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.
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.
143 if (is_setting_trap_flag(child
, regs
)) {
144 clear_tsk_thread_flag(child
, TIF_FORCED_TF
);
149 * If TF was already set, check whether it was us who set it.
150 * If not, we should never attempt a block step.
152 if (oflags
& X86_EFLAGS_TF
)
153 return test_tsk_thread_flag(child
, TIF_FORCED_TF
);
155 set_tsk_thread_flag(child
, TIF_FORCED_TF
);
160 void set_task_blockstep(struct task_struct
*task
, bool on
)
162 unsigned long debugctl
;
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.
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.
175 debugctl
= get_debugctlmsr();
177 debugctl
|= DEBUGCTLMSR_BTF
;
178 set_tsk_thread_flag(task
, TIF_BLOCKSTEP
);
180 debugctl
&= ~DEBUGCTLMSR_BTF
;
181 clear_tsk_thread_flag(task
, TIF_BLOCKSTEP
);
184 update_debugctlmsr(debugctl
);
189 * Enable single or block step.
191 static void enable_step(struct task_struct
*child
, bool block
)
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.
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);
206 void user_enable_single_step(struct task_struct
*child
)
208 enable_step(child
, 0);
211 void user_enable_block_step(struct task_struct
*child
)
213 enable_step(child
, 1);
216 void user_disable_single_step(struct task_struct
*child
)
219 * Make sure block stepping (BTF) is disabled.
221 if (test_tsk_thread_flag(child
, TIF_BLOCKSTEP
))
222 set_task_blockstep(child
, false);
224 /* Always clear TIF_SINGLESTEP... */
225 clear_tsk_thread_flag(child
, TIF_SINGLESTEP
);
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
;