![Renzo Davoli](/assets/img/avatar_default.png)
It is currently impossible to run a user-mode linux machine inside another user-mode linux (UML on UML). It breaks after a few instructions. When it tries to check whether SYSEMU is installed (the inner) UML receives an inconsistent result (from the outer UML). This is the output of a broken attempt: $ ./linux mem=256m ubd0=cow Locating the bottom of the address space ... 0x0 Locating the top of the address space ... 0xc0000000 Core dump limits : soft - 0 hard - NONE Checking that ptrace can change system call numbers...OK Checking ptrace new tags for syscall emulation...unsupported Checking syscall emulation patch for ptrace...check_sysemu : expected SIGTRAP, got status = 256 $ The problem is the following: PTRACE_SYSCALL/SINGLESTEP is currently managed inside arch_ptrace for ARCH=um. PTRACE_SYSEMU/SUSEMU_SINGLESTEP is not captured in arch_ptrace's switch, therefore it is erroneously passed back to ptrace_request (in kernel/ptrace). This simple patch simply forces ptrace to return an error on PTRACE_SYSEMU/SUSEMU_SINGLESTEP as it is unsupported on ARCH=um, and fixes the problem. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Renzo Davoli <renzo@cs.unibo.it> Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com> Cc: Jeff Dike <jdike@addtoit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
300 lines
6.8 KiB
C
300 lines
6.8 KiB
C
/*
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* Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
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* Licensed under the GPL
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*/
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#include "linux/audit.h"
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#include "linux/ptrace.h"
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#include "linux/sched.h"
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#include "asm/uaccess.h"
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#ifdef CONFIG_PROC_MM
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#include "proc_mm.h"
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#endif
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#include "skas_ptrace.h"
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static inline void set_singlestepping(struct task_struct *child, int on)
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{
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if (on)
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child->ptrace |= PT_DTRACE;
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else
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child->ptrace &= ~PT_DTRACE;
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child->thread.singlestep_syscall = 0;
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#ifdef SUBARCH_SET_SINGLESTEPPING
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SUBARCH_SET_SINGLESTEPPING(child, on);
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#endif
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}
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/*
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* Called by kernel/ptrace.c when detaching..
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*/
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void ptrace_disable(struct task_struct *child)
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{
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set_singlestepping(child,0);
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}
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extern int peek_user(struct task_struct * child, long addr, long data);
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extern int poke_user(struct task_struct * child, long addr, long data);
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long arch_ptrace(struct task_struct *child, long request, long addr, long data)
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{
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int i, ret;
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unsigned long __user *p = (void __user *)(unsigned long)data;
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switch (request) {
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/* read word at location addr. */
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case PTRACE_PEEKTEXT:
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case PTRACE_PEEKDATA:
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ret = generic_ptrace_peekdata(child, addr, data);
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break;
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/* read the word at location addr in the USER area. */
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case PTRACE_PEEKUSR:
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ret = peek_user(child, addr, data);
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break;
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/* write the word at location addr. */
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case PTRACE_POKETEXT:
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case PTRACE_POKEDATA:
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ret = generic_ptrace_pokedata(child, addr, data);
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break;
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/* write the word at location addr in the USER area */
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case PTRACE_POKEUSR:
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ret = poke_user(child, addr, data);
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break;
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case PTRACE_SYSEMU:
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case PTRACE_SYSEMU_SINGLESTEP:
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ret = -EIO;
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break;
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/* continue and stop at next (return from) syscall */
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case PTRACE_SYSCALL:
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/* restart after signal. */
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case PTRACE_CONT: {
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ret = -EIO;
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if (!valid_signal(data))
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break;
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set_singlestepping(child, 0);
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if (request == PTRACE_SYSCALL)
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set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
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else clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
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child->exit_code = data;
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wake_up_process(child);
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ret = 0;
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break;
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}
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/*
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* make the child exit. Best I can do is send it a sigkill.
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* perhaps it should be put in the status that it wants to
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* exit.
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*/
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case PTRACE_KILL: {
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ret = 0;
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if (child->exit_state == EXIT_ZOMBIE) /* already dead */
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break;
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set_singlestepping(child, 0);
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child->exit_code = SIGKILL;
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wake_up_process(child);
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break;
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}
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case PTRACE_SINGLESTEP: { /* set the trap flag. */
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ret = -EIO;
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if (!valid_signal(data))
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break;
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clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
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set_singlestepping(child, 1);
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child->exit_code = data;
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/* give it a chance to run. */
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wake_up_process(child);
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ret = 0;
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break;
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}
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#ifdef PTRACE_GETREGS
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case PTRACE_GETREGS: { /* Get all gp regs from the child. */
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if (!access_ok(VERIFY_WRITE, p, MAX_REG_OFFSET)) {
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ret = -EIO;
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break;
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}
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for ( i = 0; i < MAX_REG_OFFSET; i += sizeof(long) ) {
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__put_user(getreg(child, i), p);
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p++;
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}
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ret = 0;
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break;
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}
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#endif
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#ifdef PTRACE_SETREGS
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case PTRACE_SETREGS: { /* Set all gp regs in the child. */
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unsigned long tmp = 0;
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if (!access_ok(VERIFY_READ, p, MAX_REG_OFFSET)) {
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ret = -EIO;
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break;
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}
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for ( i = 0; i < MAX_REG_OFFSET; i += sizeof(long) ) {
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__get_user(tmp, p);
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putreg(child, i, tmp);
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p++;
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}
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ret = 0;
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break;
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}
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#endif
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#ifdef PTRACE_GETFPREGS
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case PTRACE_GETFPREGS: /* Get the child FPU state. */
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ret = get_fpregs((struct user_i387_struct __user *) data,
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child);
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break;
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#endif
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#ifdef PTRACE_SETFPREGS
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case PTRACE_SETFPREGS: /* Set the child FPU state. */
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ret = set_fpregs((struct user_i387_struct __user *) data,
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child);
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break;
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#endif
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case PTRACE_GET_THREAD_AREA:
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ret = ptrace_get_thread_area(child, addr,
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(struct user_desc __user *) data);
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break;
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case PTRACE_SET_THREAD_AREA:
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ret = ptrace_set_thread_area(child, addr,
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(struct user_desc __user *) data);
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break;
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case PTRACE_FAULTINFO: {
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/*
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* Take the info from thread->arch->faultinfo,
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* but transfer max. sizeof(struct ptrace_faultinfo).
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* On i386, ptrace_faultinfo is smaller!
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*/
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ret = copy_to_user(p, &child->thread.arch.faultinfo,
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sizeof(struct ptrace_faultinfo));
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break;
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}
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#ifdef PTRACE_LDT
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case PTRACE_LDT: {
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struct ptrace_ldt ldt;
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if (copy_from_user(&ldt, p, sizeof(ldt))) {
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ret = -EIO;
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break;
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}
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/*
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* This one is confusing, so just punt and return -EIO for
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* now
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*/
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ret = -EIO;
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break;
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}
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#endif
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#ifdef CONFIG_PROC_MM
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case PTRACE_SWITCH_MM: {
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struct mm_struct *old = child->mm;
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struct mm_struct *new = proc_mm_get_mm(data);
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if (IS_ERR(new)) {
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ret = PTR_ERR(new);
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break;
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}
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atomic_inc(&new->mm_users);
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child->mm = new;
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child->active_mm = new;
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mmput(old);
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ret = 0;
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break;
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}
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#endif
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#ifdef PTRACE_ARCH_PRCTL
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case PTRACE_ARCH_PRCTL:
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/* XXX Calls ptrace on the host - needs some SMP thinking */
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ret = arch_prctl(child, data, (void *) addr);
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break;
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#endif
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default:
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ret = ptrace_request(child, request, addr, data);
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if (ret == -EIO)
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ret = subarch_ptrace(child, request, addr, data);
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break;
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}
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return ret;
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}
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static void send_sigtrap(struct task_struct *tsk, struct uml_pt_regs *regs,
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int error_code)
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{
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struct siginfo info;
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memset(&info, 0, sizeof(info));
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info.si_signo = SIGTRAP;
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info.si_code = TRAP_BRKPT;
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/* User-mode eip? */
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info.si_addr = UPT_IS_USER(regs) ? (void __user *) UPT_IP(regs) : NULL;
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/* Send us the fake SIGTRAP */
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force_sig_info(SIGTRAP, &info, tsk);
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}
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/*
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* XXX Check PT_DTRACE vs TIF_SINGLESTEP for singlestepping check and
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* PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
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*/
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void syscall_trace(struct uml_pt_regs *regs, int entryexit)
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{
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int is_singlestep = (current->ptrace & PT_DTRACE) && entryexit;
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int tracesysgood;
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if (unlikely(current->audit_context)) {
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if (!entryexit)
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audit_syscall_entry(HOST_AUDIT_ARCH,
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UPT_SYSCALL_NR(regs),
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UPT_SYSCALL_ARG1(regs),
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UPT_SYSCALL_ARG2(regs),
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UPT_SYSCALL_ARG3(regs),
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UPT_SYSCALL_ARG4(regs));
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else audit_syscall_exit(AUDITSC_RESULT(UPT_SYSCALL_RET(regs)),
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UPT_SYSCALL_RET(regs));
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}
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/* Fake a debug trap */
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if (is_singlestep)
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send_sigtrap(current, regs, 0);
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if (!test_thread_flag(TIF_SYSCALL_TRACE))
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return;
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if (!(current->ptrace & PT_PTRACED))
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return;
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/*
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* the 0x80 provides a way for the tracing parent to distinguish
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* between a syscall stop and SIGTRAP delivery
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*/
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tracesysgood = (current->ptrace & PT_TRACESYSGOOD);
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ptrace_notify(SIGTRAP | (tracesysgood ? 0x80 : 0));
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if (entryexit) /* force do_signal() --> is_syscall() */
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set_thread_flag(TIF_SIGPENDING);
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/*
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* this isn't the same as continuing with a signal, but it will do
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* for normal use. strace only continues with a signal if the
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* stopping signal is not SIGTRAP. -brl
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*/
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if (current->exit_code) {
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send_sig(current->exit_code, current, 1);
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current->exit_code = 0;
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}
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}
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