signal.c

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/*
 * Based on arch/arm/kernel/signal.c
 *
 * Copyright (C) 1995-2009 Russell King
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/freezer.h>
#include <linux/uaccess.h>
#include <linux/tracehook.h>
#include <linux/ratelimit.h>

#include <asm/compat.h>
#include <asm/debug-monitors.h>
#include <asm/elf.h>
#include <asm/cacheflush.h>
#include <asm/ucontext.h>
#include <asm/unistd.h>
#include <asm/fpsimd.h>
#include <asm/signal32.h>
#include <asm/vdso.h>

/*
 * Do a signal return; undo the signal stack. These are aligned to 128-bit.
 */
struct rt_sigframe {
    struct siginfo info;
    struct ucontext uc;
};

static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
{
    struct fpsimd_state *fpsimd = &current->thread.fpsimd_state;
    int err;

    /* dump the hardware registers to the fpsimd_state structure */
    fpsimd_save_state(fpsimd);

    /* copy the FP and status/control registers */
    err = __copy_to_user(ctx->vregs, fpsimd->vregs, sizeof(fpsimd->vregs));
    __put_user_error(fpsimd->fpsr, &ctx->fpsr, err);
    __put_user_error(fpsimd->fpcr, &ctx->fpcr, err);

    /* copy the magic/size information */
    __put_user_error(FPSIMD_MAGIC, &ctx->head.magic, err);
    __put_user_error(sizeof(struct fpsimd_context), &ctx->head.size, err);

    return err ? -EFAULT : 0;
}

static int restore_fpsimd_context(struct fpsimd_context __user *ctx)
{
    struct fpsimd_state fpsimd;
    __u32 magic, size;
    int err = 0;

    /* check the magic/size information */
    __get_user_error(magic, &ctx->head.magic, err);
    __get_user_error(size, &ctx->head.size, err);
    if (err)
        return -EFAULT;
    if (magic != FPSIMD_MAGIC || size != sizeof(struct fpsimd_context))
        return -EINVAL;

    /* copy the FP and status/control registers */
    err = __copy_from_user(fpsimd.vregs, ctx->vregs,
                   sizeof(fpsimd.vregs));
    __get_user_error(fpsimd.fpsr, &ctx->fpsr, err);
    __get_user_error(fpsimd.fpcr, &ctx->fpcr, err);

    /* load the hardware registers from the fpsimd_state structure */
    if (!err) {
        preempt_disable();
        fpsimd_load_state(&fpsimd);
        preempt_enable();
    }

    return err ? -EFAULT : 0;
}

static int restore_sigframe(struct pt_regs *regs,
                struct rt_sigframe __user *sf)
{
    sigset_t set;
    int i, err;
    struct aux_context __user *aux =
        (struct aux_context __user *)sf->uc.uc_mcontext.__reserved;

    err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
    if (err == 0)
        set_current_blocked(&set);

    for (i = 0; i < 31; i++)
        __get_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i],
                 err);
    __get_user_error(regs->sp, &sf->uc.uc_mcontext.sp, err);
    __get_user_error(regs->pc, &sf->uc.uc_mcontext.pc, err);
    __get_user_error(regs->pstate, &sf->uc.uc_mcontext.pstate, err);

    /*
     * Avoid sys_rt_sigreturn() restarting.
     */
    regs->syscallno = ~0UL;

    err |= !valid_user_regs(&regs->user_regs);

    if (err == 0)
        err |= restore_fpsimd_context(&aux->fpsimd);

    return err;
}

asmlinkage long sys_rt_sigreturn(struct pt_regs *regs)
{
    struct rt_sigframe __user *frame;

    /* Always make any pending restarted system calls return -EINTR */
    current_thread_info()->restart_block.fn = do_no_restart_syscall;

    /*
     * Since we stacked the signal on a 128-bit boundary, then 'sp' should
     * be word aligned here.
     */
    if (regs->sp & 15)
        goto badframe;

    frame = (struct rt_sigframe __user *)regs->sp;

    if (!access_ok(VERIFY_READ, frame, sizeof (*frame)))
        goto badframe;

    if (restore_sigframe(regs, frame))
        goto badframe;

    if (do_sigaltstack(&frame->uc.uc_stack,
               NULL, regs->sp) == -EFAULT)
        goto badframe;

    return regs->regs[0];

badframe:
    if (show_unhandled_signals)
        pr_info_ratelimited("%s[%d]: bad frame in %s: pc=%08llx sp=%08llx\n",
                    current->comm, task_pid_nr(current), __func__,
                    regs->pc, regs->sp);
    force_sig(SIGSEGV, current);
    return 0;
}

asmlinkage long sys_sigaltstack(const stack_t __user *uss, stack_t __user *uoss,
                unsigned long sp)
{
    return do_sigaltstack(uss, uoss, sp);
}

static int setup_sigframe(struct rt_sigframe __user *sf,
              struct pt_regs *regs, sigset_t *set)
{
    int i, err = 0;
    struct aux_context __user *aux =
        (struct aux_context __user *)sf->uc.uc_mcontext.__reserved;

    for (i = 0; i < 31; i++)
        __put_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i],
                 err);
    __put_user_error(regs->sp, &sf->uc.uc_mcontext.sp, err);
    __put_user_error(regs->pc, &sf->uc.uc_mcontext.pc, err);
    __put_user_error(regs->pstate, &sf->uc.uc_mcontext.pstate, err);

    __put_user_error(current->thread.fault_address, &sf->uc.uc_mcontext.fault_address, err);

    err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set));

    if (err == 0)
        err |= preserve_fpsimd_context(&aux->fpsimd);

    /* set the "end" magic */
    __put_user_error(0, &aux->end.magic, err);
    __put_user_error(0, &aux->end.size, err);

    return err;
}

static void __user *get_sigframe(struct k_sigaction *ka, struct pt_regs *regs,
                 int framesize)
{
    unsigned long sp, sp_top;
    void __user *frame;

    sp = sp_top = regs->sp;

    /*
     * This is the X/Open sanctioned signal stack switching.
     */
    if ((ka->sa.sa_flags & SA_ONSTACK) && !sas_ss_flags(sp))
        sp = sp_top = current->sas_ss_sp + current->sas_ss_size;

    /* room for stack frame (FP, LR) */
    sp -= 16;

    sp = (sp - framesize) & ~15;
    frame = (void __user *)sp;

    /*
     * Check that we can actually write to the signal frame.
     */
    if (!access_ok(VERIFY_WRITE, frame, sp_top - sp))
        frame = NULL;

    return frame;
}

static int setup_return(struct pt_regs *regs, struct k_sigaction *ka,
            void __user *frame, int usig)
{
    int err = 0;
    __sigrestore_t sigtramp;
    unsigned long __user *sp = (unsigned long __user *)regs->sp;

    /* set up the stack frame */
    __put_user_error(regs->regs[29], sp - 2, err);
    __put_user_error(regs->regs[30], sp - 1, err);

    regs->regs[0] = usig;
    regs->regs[29] = regs->sp - 16;
    regs->sp = (unsigned long)frame;
    regs->pc = (unsigned long)ka->sa.sa_handler;

    if (ka->sa.sa_flags & SA_RESTORER)
        sigtramp = ka->sa.sa_restorer;
    else
        sigtramp = VDSO_SYMBOL(current->mm->context.vdso, sigtramp);

    regs->regs[30] = (unsigned long)sigtramp;

    return err;
}

static int setup_rt_frame(int usig, struct k_sigaction *ka, siginfo_t *info,
              sigset_t *set, struct pt_regs *regs)
{
    struct rt_sigframe __user *frame;
    stack_t stack;
    int err = 0;

    frame = get_sigframe(ka, regs, sizeof(*frame));
    if (!frame)
        return 1;

    __put_user_error(0, &frame->uc.uc_flags, err);
    __put_user_error(NULL, &frame->uc.uc_link, err);

    memset(&stack, 0, sizeof(stack));
    stack.ss_sp = (void __user *)current->sas_ss_sp;
    stack.ss_flags = sas_ss_flags(regs->sp);
    stack.ss_size = current->sas_ss_size;
    err |= __copy_to_user(&frame->uc.uc_stack, &stack, sizeof(stack));

    err |= setup_sigframe(frame, regs, set);
    if (err == 0)
        err = setup_return(regs, ka, frame, usig);

    if (err == 0 && ka->sa.sa_flags & SA_SIGINFO) {
        err |= copy_siginfo_to_user(&frame->info, info);
        regs->regs[1] = (unsigned long)&frame->info;
        regs->regs[2] = (unsigned long)&frame->uc;
    }

    return err;
}

static void setup_restart_syscall(struct pt_regs *regs)
{
    if (is_compat_task())
        compat_setup_restart_syscall(regs);
    else
        regs->regs[8] = __NR_restart_syscall;
}

/*
 * OK, we're invoking a handler
 */
static void handle_signal(unsigned long sig, struct k_sigaction *ka,
              siginfo_t *info, struct pt_regs *regs)
{
    struct thread_info *thread = current_thread_info();
    struct task_struct *tsk = current;
    sigset_t *oldset = sigmask_to_save();
    int usig = sig;
    int ret;

    /*
     * translate the signal
     */
    if (usig < 32 && thread->exec_domain && thread->exec_domain->signal_invmap)
        usig = thread->exec_domain->signal_invmap[usig];

    /*
     * Set up the stack frame
     */
    if (is_compat_task()) {
        if (ka->sa.sa_flags & SA_SIGINFO)
            ret = compat_setup_rt_frame(usig, ka, info, oldset,
                            regs);
        else
            ret = compat_setup_frame(usig, ka, oldset, regs);
    } else {
        ret = setup_rt_frame(usig, ka, info, oldset, regs);
    }

    /*
     * Check that the resulting registers are actually sane.
     */
    ret |= !valid_user_regs(&regs->user_regs);

    if (ret != 0) {
        force_sigsegv(sig, tsk);
        return;
    }

    /*
     * Fast forward the stepping logic so we step into the signal
     * handler.
     */
    user_fastforward_single_step(tsk);

    signal_delivered(sig, info, ka, regs, 0);
}

/*
 * Note that 'init' is a special process: it doesn't get signals it doesn't
 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 * mistake.
 *
 * Note that we go through the signals twice: once to check the signals that
 * the kernel can handle, and then we build all the user-level signal handling
 * stack-frames in one go after that.
 */
static void do_signal(struct pt_regs *regs)
{
    unsigned long continue_addr = 0, restart_addr = 0;
    struct k_sigaction ka;
    siginfo_t info;
    int signr, retval = 0;
    int syscall = (int)regs->syscallno;

    /*
     * If we were from a system call, check for system call restarting...
     */
    if (syscall >= 0) {
        continue_addr = regs->pc;
        restart_addr = continue_addr - (compat_thumb_mode(regs) ? 2 : 4);
        retval = regs->regs[0];

        /*
         * Avoid additional syscall restarting via ret_to_user.
         */
        regs->syscallno = ~0UL;

        /*
         * Prepare for system call restart. We do this here so that a
         * debugger will see the already changed PC.
         */
        switch (retval) {
        case -ERESTARTNOHAND:
        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTART_RESTARTBLOCK:
            regs->regs[0] = regs->orig_x0;
            regs->pc = restart_addr;
            break;
        }
    }

    /*
     * Get the signal to deliver. When running under ptrace, at this point
     * the debugger may change all of our registers.
     */
    signr = get_signal_to_deliver(&info, &ka, regs, NULL);
    if (signr > 0) {
        /*
         * Depending on the signal settings, we may need to revert the
         * decision to restart the system call, but skip this if a
         * debugger has chosen to restart at a different PC.
         */
        if (regs->pc == restart_addr &&
            (retval == -ERESTARTNOHAND ||
             retval == -ERESTART_RESTARTBLOCK ||
             (retval == -ERESTARTSYS &&
              !(ka.sa.sa_flags & SA_RESTART)))) {
            regs->regs[0] = -EINTR;
            regs->pc = continue_addr;
        }

        handle_signal(signr, &ka, &info, regs);
        return;
    }

    /*
     * Handle restarting a different system call. As above, if a debugger
     * has chosen to restart at a different PC, ignore the restart.
     */
    if (syscall >= 0 && regs->pc == restart_addr) {
        if (retval == -ERESTART_RESTARTBLOCK)
            setup_restart_syscall(regs);
        user_rewind_single_step(current);
    }

    restore_saved_sigmask();
}

asmlinkage void do_notify_resume(struct pt_regs *regs,
                 unsigned int thread_flags)
{
    if (thread_flags & _TIF_SIGPENDING)
        do_signal(regs);

    if (thread_flags & _TIF_NOTIFY_RESUME) {
        clear_thread_flag(TIF_NOTIFY_RESUME);
        tracehook_notify_resume(regs);
    }
}