Handle bogus %cs selector in single-step instruction decoding (CVE-2007-3731)

[linux-2.6.22.y-op.git] / arch / i386 / kernel / ptrace.c

/* ptrace.c */
/* By Ross Biro 1/23/92 */
/*
 * Pentium III FXSR, SSE support
 *      Gareth Hughes <gareth@valinux.com>, May 2000
 */

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/errno.h>
#include <linux/ptrace.h>
#include <linux/user.h>
#include <linux/security.h>
#include <linux/audit.h>
#include <linux/seccomp.h>
#include <linux/signal.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/system.h>
#include <asm/processor.h>
#include <asm/i387.h>
#include <asm/debugreg.h>
#include <asm/ldt.h>
#include <asm/desc.h>

/*
 * does not yet catch signals sent when the child dies.
 * in exit.c or in signal.c.
 */

/*
 * Determines which flags the user has access to [1 = access, 0 = no access].
 * Prohibits changing ID(21), VIP(20), VIF(19), VM(17), NT(14), IOPL(12-13), IF(9).
 * Also masks reserved bits (31-22, 15, 5, 3, 1).
 */
#define FLAG_MASK 0x00050dd5

/* set's the trap flag. */
#define TRAP_FLAG 0x100

/*
 * Offset of eflags on child stack..
 */
#define EFL_OFFSET offsetof(struct pt_regs, eflags)

static inline struct pt_regs *get_child_regs(struct task_struct *task)
{
        void *stack_top = (void *)task->thread.esp0;
        return stack_top - sizeof(struct pt_regs);
}

/*
 * This routine will get a word off of the processes privileged stack.
 * the offset is bytes into the pt_regs structure on the stack.
 * This routine assumes that all the privileged stacks are in our
 * data space.
 */   
static inline int get_stack_long(struct task_struct *task, int offset)
{
        unsigned char *stack;

        stack = (unsigned char *)task->thread.esp0 - sizeof(struct pt_regs);
        stack += offset;
        return (*((int *)stack));
}

/*
 * This routine will put a word on the processes privileged stack.
 * the offset is bytes into the pt_regs structure on the stack.
 * This routine assumes that all the privileged stacks are in our
 * data space.
 */
static inline int put_stack_long(struct task_struct *task, int offset,
        unsigned long data)
{
        unsigned char * stack;

        stack = (unsigned char *)task->thread.esp0 - sizeof(struct pt_regs);
        stack += offset;
        *(unsigned long *) stack = data;
        return 0;
}

static int putreg(struct task_struct *child,
        unsigned long regno, unsigned long value)
{
        switch (regno >> 2) {
                case GS:
                        if (value && (value & 3) != 3)
                                return -EIO;
                        child->thread.gs = value;
                        return 0;
                case DS:
                case ES:
                case FS:
                        if (value && (value & 3) != 3)
                                return -EIO;
                        value &= 0xffff;
                        break;
                case SS:
                case CS:
                        if ((value & 3) != 3)
                                return -EIO;
                        value &= 0xffff;
                        break;
                case EFL:
                        value &= FLAG_MASK;
                        value |= get_stack_long(child, EFL_OFFSET) & ~FLAG_MASK;
                        break;
        }
        if (regno > FS*4)
                regno -= 1*4;
        put_stack_long(child, regno, value);
        return 0;
}

static unsigned long getreg(struct task_struct *child,
        unsigned long regno)
{
        unsigned long retval = ~0UL;

        switch (regno >> 2) {
                case GS:
                        retval = child->thread.gs;
                        break;
                case DS:
                case ES:
                case FS:
                case SS:
                case CS:
                        retval = 0xffff;
                        /* fall through */
                default:
                        if (regno > FS*4)
                                regno -= 1*4;
                        retval &= get_stack_long(child, regno);
        }
        return retval;
}

#define LDT_SEGMENT 4

static unsigned long convert_eip_to_linear(struct task_struct *child, struct pt_regs *regs)
{
        unsigned long addr, seg;

        addr = regs->eip;
        seg = regs->xcs & 0xffff;
        if (regs->eflags & VM_MASK) {
                addr = (addr & 0xffff) + (seg << 4);
                return addr;
        }

        /*
         * 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 & LDT_SEGMENT) {
                u32 *desc;
                unsigned long base;

                seg &= ~7UL;

                down(&child->mm->context.sem);
                if (unlikely((seg >> 3) >= child->mm->context.size))
                        addr = -1L; /* bogus selector, access would fault */
                else {
                        desc = child->mm->context.ldt + seg;
                        base = ((desc[0] >> 16) |
                                ((desc[1] & 0xff) << 16) |
                                (desc[1] & 0xff000000));

                        /* 16-bit code segment? */
                        if (!((desc[1] >> 22) & 1))
                                addr &= 0xffff;
                        addr += base;
                }
                up(&child->mm->context.sem);
        }
        return addr;
}

static inline int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
{
        int i, copied;
        unsigned char opcode[15];
        unsigned long addr = convert_eip_to_linear(child, regs);

        copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0);
        for (i = 0; i < copied; i++) {
                switch (opcode[i]) {
                /* popf and iret */
                case 0x9d: case 0xcf:
                        return 1;
                /* 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;

                /*
                 * 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;
}

static void set_singlestep(struct task_struct *child)
{
        struct pt_regs *regs = get_child_regs(child);

        /*
         * 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);

        /*
         * If TF was already set, don't do anything else
         */
        if (regs->eflags & TRAP_FLAG)
                return;

        /* Set TF on the kernel stack.. */
        regs->eflags |= TRAP_FLAG;

        /*
         * ..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.
         */
        if (is_setting_trap_flag(child, regs))
                return;
        
        child->ptrace |= PT_DTRACE;
}

static void clear_singlestep(struct task_struct *child)
{
        /* Always clear TIF_SINGLESTEP... */
        clear_tsk_thread_flag(child, TIF_SINGLESTEP);

        /* But touch TF only if it was set by us.. */
        if (child->ptrace & PT_DTRACE) {
                struct pt_regs *regs = get_child_regs(child);
                regs->eflags &= ~TRAP_FLAG;
                child->ptrace &= ~PT_DTRACE;
        }
}

/*
 * Called by kernel/ptrace.c when detaching..
 *
 * Make sure the single step bit is not set.
 */
void ptrace_disable(struct task_struct *child)
{ 
        clear_singlestep(child);
        clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
        clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
}

/*
 * Perform get_thread_area on behalf of the traced child.
 */
static int
ptrace_get_thread_area(struct task_struct *child,
                       int idx, struct user_desc __user *user_desc)
{
        struct user_desc info;
        struct desc_struct *desc;

/*
 * Get the current Thread-Local Storage area:
 */

#define GET_BASE(desc) ( \
        (((desc)->a >> 16) & 0x0000ffff) | \
        (((desc)->b << 16) & 0x00ff0000) | \
        ( (desc)->b        & 0xff000000)   )

#define GET_LIMIT(desc) ( \
        ((desc)->a & 0x0ffff) | \
         ((desc)->b & 0xf0000) )

#define GET_32BIT(desc)         (((desc)->b >> 22) & 1)
#define GET_CONTENTS(desc)      (((desc)->b >> 10) & 3)
#define GET_WRITABLE(desc)      (((desc)->b >>  9) & 1)
#define GET_LIMIT_PAGES(desc)   (((desc)->b >> 23) & 1)
#define GET_PRESENT(desc)       (((desc)->b >> 15) & 1)
#define GET_USEABLE(desc)       (((desc)->b >> 20) & 1)

        if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
                return -EINVAL;

        desc = child->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;

        info.entry_number = idx;
        info.base_addr = GET_BASE(desc);
        info.limit = GET_LIMIT(desc);
        info.seg_32bit = GET_32BIT(desc);
        info.contents = GET_CONTENTS(desc);
        info.read_exec_only = !GET_WRITABLE(desc);
        info.limit_in_pages = GET_LIMIT_PAGES(desc);
        info.seg_not_present = !GET_PRESENT(desc);
        info.useable = GET_USEABLE(desc);

        if (copy_to_user(user_desc, &info, sizeof(info)))
                return -EFAULT;

        return 0;
}

/*
 * Perform set_thread_area on behalf of the traced child.
 */
static int
ptrace_set_thread_area(struct task_struct *child,
                       int idx, struct user_desc __user *user_desc)
{
        struct user_desc info;
        struct desc_struct *desc;

        if (copy_from_user(&info, user_desc, sizeof(info)))
                return -EFAULT;

        if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
                return -EINVAL;

        desc = child->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;
        if (LDT_empty(&info)) {
                desc->a = 0;
                desc->b = 0;
        } else {
                desc->a = LDT_entry_a(&info);
                desc->b = LDT_entry_b(&info);
        }

        return 0;
}

long arch_ptrace(struct task_struct *child, long request, long addr, long data)
{
        struct user * dummy = NULL;
        int i, ret;
        unsigned long __user *datap = (unsigned long __user *)data;

        switch (request) {
        /* when I and D space are separate, these will need to be fixed. */
        case PTRACE_PEEKTEXT: /* read word at location addr. */ 
        case PTRACE_PEEKDATA: {
                unsigned long tmp;
                int copied;

                copied = access_process_vm(child, addr, &tmp, sizeof(tmp), 0);
                ret = -EIO;
                if (copied != sizeof(tmp))
                        break;
                ret = put_user(tmp, datap);
                break;
        }

        /* read the word at location addr in the USER area. */
        case PTRACE_PEEKUSR: {
                unsigned long tmp;

                ret = -EIO;
                if ((addr & 3) || addr < 0 || 
                    addr > sizeof(struct user) - 3)
                        break;

                tmp = 0;  /* Default return condition */
                if(addr < FRAME_SIZE*sizeof(long))
                        tmp = getreg(child, addr);
                if(addr >= (long) &dummy->u_debugreg[0] &&
                   addr <= (long) &dummy->u_debugreg[7]){
                        addr -= (long) &dummy->u_debugreg[0];
                        addr = addr >> 2;
                        tmp = child->thread.debugreg[addr];
                }
                ret = put_user(tmp, datap);
                break;
        }

        /* when I and D space are separate, this will have to be fixed. */
        case PTRACE_POKETEXT: /* write the word at location addr. */
        case PTRACE_POKEDATA:
                ret = 0;
                if (access_process_vm(child, addr, &data, sizeof(data), 1) == sizeof(data))
                        break;
                ret = -EIO;
                break;

        case PTRACE_POKEUSR: /* write the word at location addr in the USER area */
                ret = -EIO;
                if ((addr & 3) || addr < 0 || 
                    addr > sizeof(struct user) - 3)
                        break;

                if (addr < FRAME_SIZE*sizeof(long)) {
                        ret = putreg(child, addr, data);
                        break;
                }
                /* We need to be very careful here.  We implicitly
                   want to modify a portion of the task_struct, and we
                   have to be selective about what portions we allow someone
                   to modify. */

                  ret = -EIO;
                  if(addr >= (long) &dummy->u_debugreg[0] &&
                     addr <= (long) &dummy->u_debugreg[7]){

                          if(addr == (long) &dummy->u_debugreg[4]) break;
                          if(addr == (long) &dummy->u_debugreg[5]) break;
                          if(addr < (long) &dummy->u_debugreg[4] &&
                             ((unsigned long) data) >= TASK_SIZE-3) break;
                          
                          /* Sanity-check data. Take one half-byte at once with
                           * check = (val >> (16 + 4*i)) & 0xf. It contains the
                           * R/Wi and LENi bits; bits 0 and 1 are R/Wi, and bits
                           * 2 and 3 are LENi. Given a list of invalid values,
                           * we do mask |= 1 << invalid_value, so that
                           * (mask >> check) & 1 is a correct test for invalid
                           * values.
                           *
                           * R/Wi contains the type of the breakpoint /
                           * watchpoint, LENi contains the length of the watched
                           * data in the watchpoint case.
                           *
                           * The invalid values are:
                           * - LENi == 0x10 (undefined), so mask |= 0x0f00.
                           * - R/Wi == 0x10 (break on I/O reads or writes), so
                           *   mask |= 0x4444.
                           * - R/Wi == 0x00 && LENi != 0x00, so we have mask |=
                           *   0x1110.
                           *
                           * Finally, mask = 0x0f00 | 0x4444 | 0x1110 == 0x5f54.
                           *
                           * See the Intel Manual "System Programming Guide",
                           * 15.2.4
                           *
                           * Note that LENi == 0x10 is defined on x86_64 in long
                           * mode (i.e. even for 32-bit userspace software, but
                           * 64-bit kernel), so the x86_64 mask value is 0x5454.
                           * See the AMD manual no. 24593 (AMD64 System
                           * Programming)*/

                          if(addr == (long) &dummy->u_debugreg[7]) {
                                  data &= ~DR_CONTROL_RESERVED;
                                  for(i=0; i<4; i++)
                                          if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
                                                  goto out_tsk;
                                  if (data)
                                          set_tsk_thread_flag(child, TIF_DEBUG);
                                  else
                                          clear_tsk_thread_flag(child, TIF_DEBUG);
                          }
                          addr -= (long) &dummy->u_debugreg;
                          addr = addr >> 2;
                          child->thread.debugreg[addr] = data;
                          ret = 0;
                  }
                  break;

        case PTRACE_SYSEMU: /* continue and stop at next syscall, which will not be executed */
        case PTRACE_SYSCALL:    /* continue and stop at next (return from) syscall */
        case PTRACE_CONT:       /* restart after signal. */
                ret = -EIO;
                if (!valid_signal(data))
                        break;
                if (request == PTRACE_SYSEMU) {
                        set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
                        clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
                } else if (request == PTRACE_SYSCALL) {
                        set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
                        clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
                } else {
                        clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
                        clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
                }
                child->exit_code = data;
                /* make sure the single step bit is not set. */
                clear_singlestep(child);
                wake_up_process(child);
                ret = 0;
                break;

/*
 * make the child exit.  Best I can do is send it a sigkill. 
 * perhaps it should be put in the status that it wants to 
 * exit.
 */
        case PTRACE_KILL:
                ret = 0;
                if (child->exit_state == EXIT_ZOMBIE)   /* already dead */
                        break;
                child->exit_code = SIGKILL;
                /* make sure the single step bit is not set. */
                clear_singlestep(child);
                wake_up_process(child);
                break;

        case PTRACE_SYSEMU_SINGLESTEP: /* Same as SYSEMU, but singlestep if not syscall */
        case PTRACE_SINGLESTEP: /* set the trap flag. */
                ret = -EIO;
                if (!valid_signal(data))
                        break;

                if (request == PTRACE_SYSEMU_SINGLESTEP)
                        set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
                else
                        clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);

                clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
                set_singlestep(child);
                child->exit_code = data;
                /* give it a chance to run. */
                wake_up_process(child);
                ret = 0;
                break;

        case PTRACE_DETACH:
                /* detach a process that was attached. */
                ret = ptrace_detach(child, data);
                break;

        case PTRACE_GETREGS: { /* Get all gp regs from the child. */
                if (!access_ok(VERIFY_WRITE, datap, FRAME_SIZE*sizeof(long))) {
                        ret = -EIO;
                        break;
                }
                for ( i = 0; i < FRAME_SIZE*sizeof(long); i += sizeof(long) ) {
                        __put_user(getreg(child, i), datap);
                        datap++;
                }
                ret = 0;
                break;
        }

        case PTRACE_SETREGS: { /* Set all gp regs in the child. */
                unsigned long tmp;
                if (!access_ok(VERIFY_READ, datap, FRAME_SIZE*sizeof(long))) {
                        ret = -EIO;
                        break;
                }
                for ( i = 0; i < FRAME_SIZE*sizeof(long); i += sizeof(long) ) {
                        __get_user(tmp, datap);
                        putreg(child, i, tmp);
                        datap++;
                }
                ret = 0;
                break;
        }

        case PTRACE_GETFPREGS: { /* Get the child FPU state. */
                if (!access_ok(VERIFY_WRITE, datap,
                               sizeof(struct user_i387_struct))) {
                        ret = -EIO;
                        break;
                }
                ret = 0;
                if (!tsk_used_math(child))
                        init_fpu(child);
                get_fpregs((struct user_i387_struct __user *)data, child);
                break;
        }

        case PTRACE_SETFPREGS: { /* Set the child FPU state. */
                if (!access_ok(VERIFY_READ, datap,
                               sizeof(struct user_i387_struct))) {
                        ret = -EIO;
                        break;
                }
                set_stopped_child_used_math(child);
                set_fpregs(child, (struct user_i387_struct __user *)data);
                ret = 0;
                break;
        }

        case PTRACE_GETFPXREGS: { /* Get the child extended FPU state. */
                if (!access_ok(VERIFY_WRITE, datap,
                               sizeof(struct user_fxsr_struct))) {
                        ret = -EIO;
                        break;
                }
                if (!tsk_used_math(child))
                        init_fpu(child);
                ret = get_fpxregs((struct user_fxsr_struct __user *)data, child);
                break;
        }

        case PTRACE_SETFPXREGS: { /* Set the child extended FPU state. */
                if (!access_ok(VERIFY_READ, datap,
                               sizeof(struct user_fxsr_struct))) {
                        ret = -EIO;
                        break;
                }
                set_stopped_child_used_math(child);
                ret = set_fpxregs(child, (struct user_fxsr_struct __user *)data);
                break;
        }

        case PTRACE_GET_THREAD_AREA:
                ret = ptrace_get_thread_area(child, addr,
                                        (struct user_desc __user *) data);
                break;

        case PTRACE_SET_THREAD_AREA:
                ret = ptrace_set_thread_area(child, addr,
                                        (struct user_desc __user *) data);
                break;

        default:
                ret = ptrace_request(child, request, addr, data);
                break;
        }
 out_tsk:
        return ret;
}

void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code)
{
        struct siginfo info;

        tsk->thread.trap_no = 1;
        tsk->thread.error_code = error_code;

        memset(&info, 0, sizeof(info));
        info.si_signo = SIGTRAP;
        info.si_code = TRAP_BRKPT;

        /* User-mode eip? */
        info.si_addr = user_mode_vm(regs) ? (void __user *) regs->eip : NULL;

        /* Send us the fakey SIGTRAP */
        force_sig_info(SIGTRAP, &info, tsk);
}

/* notification of system call entry/exit
 * - triggered by current->work.syscall_trace
 */
__attribute__((regparm(3)))
int do_syscall_trace(struct pt_regs *regs, int entryexit)
{
        int is_sysemu = test_thread_flag(TIF_SYSCALL_EMU);
        /*
         * With TIF_SYSCALL_EMU set we want to ignore TIF_SINGLESTEP for syscall
         * interception
         */
        int is_singlestep = !is_sysemu && test_thread_flag(TIF_SINGLESTEP);
        int ret = 0;

        /* do the secure computing check first */
        if (!entryexit)
                secure_computing(regs->orig_eax);

        if (unlikely(current->audit_context)) {
                if (entryexit)
                        audit_syscall_exit(AUDITSC_RESULT(regs->eax),
                                                regs->eax);
                /* Debug traps, when using PTRACE_SINGLESTEP, must be sent only
                 * on the syscall exit path. Normally, when TIF_SYSCALL_AUDIT is
                 * not used, entry.S will call us only on syscall exit, not
                 * entry; so when TIF_SYSCALL_AUDIT is used we must avoid
                 * calling send_sigtrap() on syscall entry.
                 *
                 * Note that when PTRACE_SYSEMU_SINGLESTEP is used,
                 * is_singlestep is false, despite his name, so we will still do
                 * the correct thing.
                 */
                else if (is_singlestep)
                        goto out;
        }

        if (!(current->ptrace & PT_PTRACED))
                goto out;

        /* If a process stops on the 1st tracepoint with SYSCALL_TRACE
         * and then is resumed with SYSEMU_SINGLESTEP, it will come in
         * here. We have to check this and return */
        if (is_sysemu && entryexit)
                return 0;

        /* Fake a debug trap */
        if (is_singlestep)
                send_sigtrap(current, regs, 0);

        if (!test_thread_flag(TIF_SYSCALL_TRACE) && !is_sysemu)
                goto out;

        /* the 0x80 provides a way for the tracing parent to distinguish
           between a syscall stop and SIGTRAP delivery */
        /* Note that the debugger could change the result of test_thread_flag!*/
        ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD) ? 0x80:0));

        /*
         * this isn't the same as continuing with a signal, but it will do
         * for normal use.  strace only continues with a signal if the
         * stopping signal is not SIGTRAP.  -brl
         */
        if (current->exit_code) {
                send_sig(current->exit_code, current, 1);
                current->exit_code = 0;
        }
        ret = is_sysemu;
out:
        if (unlikely(current->audit_context) && !entryexit)
                audit_syscall_entry(AUDIT_ARCH_I386, regs->orig_eax,
                                    regs->ebx, regs->ecx, regs->edx, regs->esi);
        if (ret == 0)
                return 0;

        regs->orig_eax = -1; /* force skip of syscall restarting */
        if (unlikely(current->audit_context))
                audit_syscall_exit(AUDITSC_RESULT(regs->eax), regs->eax);
        return 1;
}