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Ole André Vadla Ravnås
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51358 changed files with 23120455 additions and 0 deletions
230
arch/x86/kernel/step.c
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230
arch/x86/kernel/step.c
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/*
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* x86 single-step support code, common to 32-bit and 64-bit.
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*/
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/ptrace.h>
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#include <asm/desc.h>
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unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
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{
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unsigned long addr, seg;
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addr = regs->ip;
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seg = regs->cs & 0xffff;
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if (v8086_mode(regs)) {
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addr = (addr & 0xffff) + (seg << 4);
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return addr;
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}
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/*
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* We'll assume that the code segments in the GDT
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* are all zero-based. That is largely true: the
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* TLS segments are used for data, and the PNPBIOS
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* and APM bios ones we just ignore here.
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*/
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if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
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struct desc_struct *desc;
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unsigned long base;
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seg &= ~7UL;
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mutex_lock(&child->mm->context.lock);
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if (unlikely((seg >> 3) >= child->mm->context.size))
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addr = -1L; /* bogus selector, access would fault */
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else {
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desc = child->mm->context.ldt + seg;
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base = get_desc_base(desc);
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/* 16-bit code segment? */
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if (!desc->d)
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addr &= 0xffff;
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addr += base;
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}
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mutex_unlock(&child->mm->context.lock);
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}
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return addr;
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}
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static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
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{
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int i, copied;
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unsigned char opcode[15];
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unsigned long addr = convert_ip_to_linear(child, regs);
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copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0);
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for (i = 0; i < copied; i++) {
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switch (opcode[i]) {
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/* popf and iret */
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case 0x9d: case 0xcf:
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return 1;
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/* CHECKME: 64 65 */
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/* opcode and address size prefixes */
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case 0x66: case 0x67:
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continue;
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/* irrelevant prefixes (segment overrides and repeats) */
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case 0x26: case 0x2e:
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case 0x36: case 0x3e:
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case 0x64: case 0x65:
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case 0xf0: case 0xf2: case 0xf3:
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continue;
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#ifdef CONFIG_X86_64
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case 0x40 ... 0x4f:
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if (!user_64bit_mode(regs))
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/* 32-bit mode: register increment */
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return 0;
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/* 64-bit mode: REX prefix */
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continue;
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#endif
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/* CHECKME: f2, f3 */
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/*
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* pushf: NOTE! We should probably not let
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* the user see the TF bit being set. But
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* it's more pain than it's worth to avoid
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* it, and a debugger could emulate this
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* all in user space if it _really_ cares.
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*/
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case 0x9c:
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default:
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return 0;
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}
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}
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return 0;
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}
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/*
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* Enable single-stepping. Return nonzero if user mode is not using TF itself.
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*/
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static int enable_single_step(struct task_struct *child)
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{
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struct pt_regs *regs = task_pt_regs(child);
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unsigned long oflags;
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/*
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* If we stepped into a sysenter/syscall insn, it trapped in
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* kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
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* If user-mode had set TF itself, then it's still clear from
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* do_debug() and we need to set it again to restore the user
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* state so we don't wrongly set TIF_FORCED_TF below.
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* If enable_single_step() was used last and that is what
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* set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
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* already set and our bookkeeping is fine.
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*/
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if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
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regs->flags |= X86_EFLAGS_TF;
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/*
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* Always set TIF_SINGLESTEP - this guarantees that
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* we single-step system calls etc.. This will also
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* cause us to set TF when returning to user mode.
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*/
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set_tsk_thread_flag(child, TIF_SINGLESTEP);
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oflags = regs->flags;
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/* Set TF on the kernel stack.. */
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regs->flags |= X86_EFLAGS_TF;
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/*
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* ..but if TF is changed by the instruction we will trace,
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* don't mark it as being "us" that set it, so that we
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* won't clear it by hand later.
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*
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* Note that if we don't actually execute the popf because
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* of a signal arriving right now or suchlike, we will lose
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* track of the fact that it really was "us" that set it.
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*/
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if (is_setting_trap_flag(child, regs)) {
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clear_tsk_thread_flag(child, TIF_FORCED_TF);
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return 0;
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}
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/*
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* If TF was already set, check whether it was us who set it.
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* If not, we should never attempt a block step.
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*/
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if (oflags & X86_EFLAGS_TF)
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return test_tsk_thread_flag(child, TIF_FORCED_TF);
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set_tsk_thread_flag(child, TIF_FORCED_TF);
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return 1;
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}
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void set_task_blockstep(struct task_struct *task, bool on)
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{
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unsigned long debugctl;
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/*
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* Ensure irq/preemption can't change debugctl in between.
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* Note also that both TIF_BLOCKSTEP and debugctl should
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* be changed atomically wrt preemption.
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*
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* NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if
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* task is current or it can't be running, otherwise we can race
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* with __switch_to_xtra(). We rely on ptrace_freeze_traced() but
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* PTRACE_KILL is not safe.
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*/
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local_irq_disable();
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debugctl = get_debugctlmsr();
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if (on) {
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debugctl |= DEBUGCTLMSR_BTF;
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set_tsk_thread_flag(task, TIF_BLOCKSTEP);
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} else {
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debugctl &= ~DEBUGCTLMSR_BTF;
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clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
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}
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if (task == current)
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update_debugctlmsr(debugctl);
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local_irq_enable();
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}
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/*
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* Enable single or block step.
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*/
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static void enable_step(struct task_struct *child, bool block)
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{
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/*
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* Make sure block stepping (BTF) is not enabled unless it should be.
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* Note that we don't try to worry about any is_setting_trap_flag()
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* instructions after the first when using block stepping.
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* So no one should try to use debugger block stepping in a program
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* that uses user-mode single stepping itself.
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*/
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if (enable_single_step(child) && block)
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set_task_blockstep(child, true);
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else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
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set_task_blockstep(child, false);
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}
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void user_enable_single_step(struct task_struct *child)
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{
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enable_step(child, 0);
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}
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void user_enable_block_step(struct task_struct *child)
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{
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enable_step(child, 1);
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}
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void user_disable_single_step(struct task_struct *child)
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{
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/*
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* Make sure block stepping (BTF) is disabled.
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*/
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if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
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set_task_blockstep(child, false);
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/* Always clear TIF_SINGLESTEP... */
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clear_tsk_thread_flag(child, TIF_SINGLESTEP);
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/* But touch TF only if it was set by us.. */
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if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
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task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
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}
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