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