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>

arch/arm64/include/asm/sigcontext.h

+/*
+ * 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/>.
+ */
+#ifndef __ASM_SIGCONTEXT_H
+#define __ASM_SIGCONTEXT_H
+
+#include <linux/types.h>
+
+/*
+ * Signal context structure - contains all info to do with the state
+ * before the signal handler was invoked.
+ */
+struct sigcontext {
+	__u64 fault_address;
+	/* AArch64 registers */
+	__u64 regs[31];
+	__u64 sp;
+	__u64 pc;
+	__u64 pstate;
+	/* 4K reserved for FP/SIMD state and future expansion */
+	__u8 __reserved[4096] __attribute__((__aligned__(16)));
+};
+
+/*
+ * Header to be used at the beginning of structures extending the user
+ * context. Such structures must be placed after the rt_sigframe on the stack
+ * and be 16-byte aligned. The last structure must be a dummy one with the
+ * magic and size set to 0.
+ */
+struct _aarch64_ctx {
+	__u32 magic;
+	__u32 size;
+};
+
+#define FPSIMD_MAGIC	0x46508001
+
+struct fpsimd_context {
+	struct _aarch64_ctx head;
+	__u32 fpsr;
+	__u32 fpcr;
+	__uint128_t vregs[32];
+};
+
+#ifdef __KERNEL__
+/*
+ * Auxiliary context saved in the sigcontext.__reserved array. Not exported to
+ * user space as it will change with the addition of new context. User space
+ * should check the magic/size information.
+ */
+struct aux_context {
+	struct fpsimd_context fpsimd;
+	/* additional context to be added before "end" */
+	struct _aarch64_ctx end;
+};
+#endif
+
+#endif

arch/arm64/include/asm/siginfo.h

+/*
+ * 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/>.
+ */
+#ifndef __ASM_SIGINFO_H
+#define __ASM_SIGINFO_H
+
+#define __ARCH_SI_PREAMBLE_SIZE	(4 * sizeof(int))
+
+#include <asm-generic/siginfo.h>
+
+#endif

arch/arm64/include/asm/signal.h

+/*
+ * 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/>.
+ */
+#ifndef __ASM_SIGNAL_H
+#define __ASM_SIGNAL_H
+
+/* Required for AArch32 compatibility. */
+#define SA_RESTORER	0x04000000
+
+#include <asm-generic/signal.h>
+
+#endif

arch/arm64/include/asm/ucontext.h

+/*
+ * 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/>.
+ */
+#ifndef __ASM_UCONTEXT_H
+#define __ASM_UCONTEXT_H
+
+struct ucontext {
+	unsigned long	  uc_flags;
+	struct ucontext	 *uc_link;
+	stack_t		  uc_stack;
+	sigset_t	  uc_sigmask;
+	/* glibc uses a 1024-bit sigset_t */
+	__u8		  __unused[(1024 - sizeof(sigset_t)) / 8];
+	/* last for future expansion */
+	struct sigcontext uc_mcontext;
+};
+
+#endif /* __ASM_UCONTEXT_H */

arch/arm64/kernel/signal.c

+/*
+ * 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);
+	}
+}