arm64: Signal handling support

This patch adds support for signal handling. The sigreturn is done via
VDSO, introduced by a previous patch. The SA_RESTORER is still defined
as it is required for 32-bit (compat) support but it is not to be used
for 64-bit applications.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

1 files changed, 437 insertions, 0 deletions

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
new file mode 100644
index 000000000000..8807ba2cf262
--- /dev/null
+++ b/arch/arm64/kernel/signal.c
@@ -0,0 +1,437 @@
+/*
+ * 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);
+        }
+}