[PATCH V4 14/22] LoongArch: Add signal handling support

[Huacai Chen <chenhuacai@loongson.cn>]

This patch adds signal handling support for LoongArch.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
---
 arch/loongarch/include/uapi/asm/sigcontext.h |  30 ++
 arch/loongarch/include/uapi/asm/ucontext.h   |  35 ++
 arch/loongarch/kernel/signal.c               | 454 +++++++++++++++++++
 3 files changed, 519 insertions(+)
 create mode 100644 arch/loongarch/include/uapi/asm/sigcontext.h
 create mode 100644 arch/loongarch/include/uapi/asm/ucontext.h
 create mode 100644 arch/loongarch/kernel/signal.c

diff --git a/arch/loongarch/include/uapi/asm/sigcontext.h b/arch/loongarch/include/uapi/asm/sigcontext.h
new file mode 100644
index 000000000000..5d55f61c40af
--- /dev/null
+++ b/arch/loongarch/include/uapi/asm/sigcontext.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Author: Hanlu Li <lihanlu@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.cn>
+ *
+ * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
+ */
+#ifndef _UAPI_ASM_SIGCONTEXT_H
+#define _UAPI_ASM_SIGCONTEXT_H
+
+#include <linux/types.h>
+#include <linux/posix_types.h>
+#include <asm/processor.h>
+
+/* FP context was used */
+#define USED_FP			(1 << 0)
+
+struct sigcontext {
+	__u64	sc_pc;
+	__u64	sc_regs[32];
+	__u32	sc_flags;
+	__u32	sc_fcsr;
+	__u32	sc_vcsr;
+	__u64	sc_fcc;
+	__u64	sc_scr[4];
+	union fpureg sc_fpregs[32] FPU_ALIGN;
+	__u8	sc_reserved[4096] __attribute__((__aligned__(16)));
+};
+
+#endif /* _UAPI_ASM_SIGCONTEXT_H */
diff --git a/arch/loongarch/include/uapi/asm/ucontext.h b/arch/loongarch/include/uapi/asm/ucontext.h
new file mode 100644
index 000000000000..12577e22b1c7
--- /dev/null
+++ b/arch/loongarch/include/uapi/asm/ucontext.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef __LOONGARCH_UAPI_ASM_UCONTEXT_H
+#define __LOONGARCH_UAPI_ASM_UCONTEXT_H
+
+/**
+ * struct ucontext - user context structure
+ * @uc_flags:
+ * @uc_link:
+ * @uc_stack:
+ * @uc_mcontext:	holds basic processor state
+ * @uc_sigmask:
+ * @uc_extcontext:	holds extended processor state
+ */
+struct ucontext {
+	unsigned long		uc_flags;
+	struct ucontext		*uc_link;
+	stack_t			uc_stack;
+	sigset_t		uc_sigmask;
+	/* There's some padding here to allow sigset_t to be expanded in the
+	 * future.  Though this is unlikely, other architectures put uc_sigmask
+	 * at the end of this structure and explicitly state it can be
+	 * expanded, so we didn't want to box ourselves in here. */
+	__u8		  __unused[1024 / 8 - sizeof(sigset_t)];
+	/* We can't put uc_sigmask at the end of this structure because we need
+	 * to be able to expand sigcontext in the future.  For example, the
+	 * vector ISA extension will almost certainly add ISA state.  We want
+	 * to ensure all user-visible ISA state can be saved and restored via a
+	 * ucontext, so we're putting this at the end in order to allow for
+	 * infinite extensibility.  Since we know this will be extended and we
+	 * assume sigset_t won't be extended an extreme amount, we're
+	 * prioritizing this. */
+	struct sigcontext	uc_mcontext;
+};
+
+#endif /* __LOONGARCH_UAPI_ASM_UCONTEXT_H */
diff --git a/arch/loongarch/kernel/signal.c b/arch/loongarch/kernel/signal.c
new file mode 100644
index 000000000000..2ff3a83c603f
--- /dev/null
+++ b/arch/loongarch/kernel/signal.c
@@ -0,0 +1,454 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Author: Hanlu Li <lihanlu@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.cn>
+ * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
+ *
+ * Derived from MIPS:
+ * Copyright (C) 1991, 1992  Linus Torvalds
+ * Copyright (C) 1994 - 2000  Ralf Baechle
+ * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
+ * Copyright (C) 2014, Imagination Technologies Ltd.
+ */
+#include <linux/audit.h>
+#include <linux/cache.h>
+#include <linux/context_tracking.h>
+#include <linux/irqflags.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/personality.h>
+#include <linux/smp.h>
+#include <linux/kernel.h>
+#include <linux/signal.h>
+#include <linux/errno.h>
+#include <linux/wait.h>
+#include <linux/ptrace.h>
+#include <linux/unistd.h>
+#include <linux/compiler.h>
+#include <linux/syscalls.h>
+#include <linux/uaccess.h>
+#include <linux/tracehook.h>
+
+#include <asm/asm.h>
+#include <asm/cacheflush.h>
+#include <asm/cpu-features.h>
+#include <asm/fpu.h>
+#include <asm/ucontext.h>
+#include <asm/vdso.h>
+
+#ifdef DEBUG_SIG
+#  define DEBUGP(fmt, args...) printk("%s: " fmt, __func__, ##args)
+#else
+#  define DEBUGP(fmt, args...)
+#endif
+
+/* Make sure we will not lose FPU ownership */
+#define lock_fpu_owner()	({ preempt_disable(); pagefault_disable(); })
+#define unlock_fpu_owner()	({ pagefault_enable(); preempt_enable(); })
+
+/* Assembly functions to move context to/from the FPU */
+extern asmlinkage int
+_save_fp_context(void __user *fpregs, void __user *fcc, void __user *csr);
+extern asmlinkage int
+_restore_fp_context(void __user *fpregs, void __user *fcc, void __user *csr);
+
+static int (*save_fp_context)(struct sigcontext __user *sc);
+static int (*restore_fp_context)(struct sigcontext __user *sc);
+
+struct rt_sigframe {
+	struct siginfo rs_info;
+	struct ucontext rs_uctx;
+};
+
+/*
+ * Thread saved context copy to/from a signal context presumed to be on the
+ * user stack, and therefore accessed with appropriate macros from uaccess.h.
+ */
+static int copy_fp_to_sigcontext(struct sigcontext __user *sc)
+{
+	int i;
+	int err = 0;
+	int inc = 1;
+	uint64_t __user *fcc = &sc->sc_fcc;
+	uint32_t __user *csr = &sc->sc_fcsr;
+	uint64_t __user *fpregs = (uint64_t *)&sc->sc_fpregs;
+
+	for (i = 0; i < NUM_FPU_REGS; i += inc) {
+		err |=
+		    __put_user(get_fpr64(&current->thread.fpu.fpr[i], 0),
+			       &fpregs[4*i]);
+	}
+	err |= __put_user(current->thread.fpu.fcsr, csr);
+	err |= __put_user(current->thread.fpu.fcc, fcc);
+
+	return err;
+}
+
+static int copy_fp_from_sigcontext(struct sigcontext __user *sc)
+{
+	int i;
+	int err = 0;
+	int inc = 1;
+	u64 fpr_val;
+	uint64_t __user *fcc = &sc->sc_fcc;
+	uint32_t __user *csr = &sc->sc_fcsr;
+	uint64_t __user *fpregs = (uint64_t *)&sc->sc_fpregs;
+
+	for (i = 0; i < NUM_FPU_REGS; i += inc) {
+		err |= __get_user(fpr_val, &fpregs[4*i]);
+		set_fpr64(&current->thread.fpu.fpr[i], 0, fpr_val);
+	}
+	err |= __get_user(current->thread.fpu.fcsr, csr);
+	err |= __get_user(current->thread.fpu.fcc, fcc);
+
+	return err;
+}
+
+/*
+ * Wrappers for the assembly _{save,restore}_fp_context functions.
+ */
+static int save_hw_fp_context(struct sigcontext __user *sc)
+{
+	uint64_t __user *fcc = &sc->sc_fcc;
+	uint32_t __user *fcsr = &sc->sc_fcsr;
+	uint64_t __user *fpregs = (uint64_t *)&sc->sc_fpregs;
+
+	return _save_fp_context(fpregs, fcc, fcsr);
+}
+
+static int restore_hw_fp_context(struct sigcontext __user *sc)
+{
+	uint64_t __user *fcc = &sc->sc_fcc;
+	uint32_t __user *csr = &sc->sc_fcsr;
+	uint64_t __user *fpregs = (uint64_t *)&sc->sc_fpregs;
+
+	return _restore_fp_context(fpregs, fcc, csr);
+}
+
+int fpcsr_pending(unsigned int __user *fpcsr)
+{
+	int err, sig = 0;
+	unsigned int csr, enabled;
+
+	err = __get_user(csr, fpcsr);
+	enabled = ((csr & FPU_CSR_ALL_E) << 24);
+	/*
+	 * If the signal handler set some FPU exceptions, clear it and
+	 * send SIGFPE.
+	 */
+	if (csr & enabled) {
+		csr &= ~enabled;
+		err |= __put_user(csr, fpcsr);
+		sig = SIGFPE;
+	}
+	return err ?: sig;
+}
+
+/*
+ * Helper routines
+ */
+static int protected_save_fp_context(struct sigcontext __user *sc)
+{
+	int err = 0;
+	unsigned int used;
+	uint32_t __user *fcc = &sc->sc_fcsr;
+	uint32_t __user *fcsr = &sc->sc_fcsr;
+	uint32_t __user *vcsr = &sc->sc_vcsr;
+	uint32_t __user *flags = &sc->sc_flags;
+	uint64_t __user *fpregs = (uint64_t *)&sc->sc_fpregs;
+
+	used = used_math() ? USED_FP : 0;
+	if (!used)
+		goto fp_done;
+
+	while (1) {
+		lock_fpu_owner();
+		if (is_fpu_owner())
+			err = save_fp_context(sc);
+		else
+			err |= copy_fp_to_sigcontext(sc);
+		unlock_fpu_owner();
+		if (likely(!err))
+			break;
+		/* touch the sigcontext and try again */
+		err = __put_user(0, &fpregs[0]) |
+			__put_user(0, &fpregs[32*4 - 1]) |
+			__put_user(0, fcc) |
+			__put_user(0, fcsr) |
+			__put_user(0, vcsr);
+		if (err)
+			return err;	/* really bad sigcontext */
+	}
+
+fp_done:
+	return __put_user(used, flags);
+}
+
+static int protected_restore_fp_context(struct sigcontext __user *sc)
+{
+	unsigned int used;
+	int err = 0, sig = 0, tmp __maybe_unused;
+	uint32_t __user *fcc = &sc->sc_fcsr;
+	uint32_t __user *fcsr = &sc->sc_fcsr;
+	uint32_t __user *vcsr = &sc->sc_vcsr;
+	uint32_t __user *flags = &sc->sc_flags;
+	uint64_t __user *fpregs = (uint64_t *)&sc->sc_fpregs;
+
+	err = __get_user(used, flags);
+	conditional_used_math(used & USED_FP);
+
+	/*
+	 * The signal handler may have used FPU; give it up if the program
+	 * doesn't want it following sigreturn.
+	 */
+	if (err || !(used & USED_FP))
+		lose_fpu(0);
+
+	if (err)
+		return err;
+
+	if (!(used & USED_FP))
+		goto fp_done;
+
+	err = sig = fpcsr_pending(fcsr);
+	if (err < 0)
+		return err;
+
+	while (1) {
+		lock_fpu_owner();
+		if (is_fpu_owner())
+			err = restore_fp_context(sc);
+		else
+			err |= copy_fp_from_sigcontext(sc);
+		unlock_fpu_owner();
+		if (likely(!err))
+			break;
+		/* touch the sigcontext and try again */
+		err = __get_user(tmp, &fpregs[0]) |
+			__get_user(tmp, &fpregs[32*4 - 1]) |
+			__get_user(tmp, fcc) |
+			__get_user(tmp, fcsr) |
+			__get_user(tmp, vcsr);
+		if (err)
+			break;	/* really bad sigcontext */
+	}
+
+fp_done:
+	return err ?: sig;
+}
+
+static int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
+{
+	int i, err = 0;
+
+	err |= __put_user(regs->csr_epc, &sc->sc_pc);
+
+	err |= __put_user(0, &sc->sc_regs[0]);
+	for (i = 1; i < 32; i++)
+		err |= __put_user(regs->regs[i], &sc->sc_regs[i]);
+
+	/*
+	 * Save FPU state to signal context. Signal handler
+	 * will "inherit" current FPU state.
+	 */
+	err |= protected_save_fp_context(sc);
+
+	return err;
+}
+
+static int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
+{
+	int i, err = 0;
+
+	/* Always make any pending restarted system calls return -EINTR */
+	current->restart_block.fn = do_no_restart_syscall;
+
+	err |= __get_user(regs->csr_epc, &sc->sc_pc);
+
+	for (i = 1; i < 32; i++)
+		err |= __get_user(regs->regs[i], &sc->sc_regs[i]);
+
+	return err ?: protected_restore_fp_context(sc);
+}
+
+void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
+			  size_t frame_size)
+{
+	unsigned long sp;
+
+	/* Default to using normal stack */
+	sp = regs->regs[3];
+	sp -= 32;   /* Reserve 32-bytes. */
+
+	sp = sigsp(sp, ksig);
+
+	return (void __user *)((sp - frame_size) & ALMASK);
+}
+
+/*
+ * Atomically swap in the new signal mask, and wait for a signal.
+ */
+
+asmlinkage long sys_rt_sigreturn(void)
+{
+	int sig;
+	sigset_t set;
+	struct pt_regs *regs;
+	struct rt_sigframe __user *frame;
+
+	regs = current_pt_regs();
+	frame = (struct rt_sigframe __user *)regs->regs[3];
+	if (!access_ok(frame, sizeof(*frame)))
+		goto badframe;
+	if (__copy_from_user(&set, &frame->rs_uctx.uc_sigmask, sizeof(set)))
+		goto badframe;
+
+	set_current_blocked(&set);
+
+	sig = restore_sigcontext(regs, &frame->rs_uctx.uc_mcontext);
+	if (sig < 0)
+		goto badframe;
+	else if (sig)
+		force_sig(sig);
+
+	if (restore_altstack(&frame->rs_uctx.uc_stack))
+		goto badframe;
+
+	return regs->regs[4];
+
+badframe:
+	force_sig(SIGSEGV);
+	return 0;
+}
+
+static int setup_rt_frame(void *sig_return, struct ksignal *ksig,
+			  struct pt_regs *regs, sigset_t *set)
+{
+	int err = 0;
+	struct rt_sigframe __user *frame;
+
+	frame = get_sigframe(ksig, regs, sizeof(*frame));
+	if (!access_ok(frame, sizeof(*frame)))
+		return -EFAULT;
+
+	/* Create siginfo.  */
+	err |= copy_siginfo_to_user(&frame->rs_info, &ksig->info);
+
+	/* Create the ucontext.	 */
+	err |= __put_user(0, &frame->rs_uctx.uc_flags);
+	err |= __put_user(NULL, &frame->rs_uctx.uc_link);
+	err |= __save_altstack(&frame->rs_uctx.uc_stack, regs->regs[3]);
+	err |= setup_sigcontext(regs, &frame->rs_uctx.uc_mcontext);
+	err |= __copy_to_user(&frame->rs_uctx.uc_sigmask, set, sizeof(*set));
+
+	if (err)
+		return -EFAULT;
+
+	/*
+	 * Arguments to signal handler:
+	 *
+	 *   a0 = signal number
+	 *   a1 = 0 (should be cause)
+	 *   a2 = pointer to ucontext
+	 *
+	 * $25 and c0_epc point to the signal handler, $29 points to
+	 * the struct rt_sigframe.
+	 */
+	regs->regs[4] = ksig->sig;
+	regs->regs[5] = (unsigned long) &frame->rs_info;
+	regs->regs[6] = (unsigned long) &frame->rs_uctx;
+	regs->regs[3] = (unsigned long) frame;
+	regs->regs[1] = (unsigned long) sig_return;
+	regs->csr_epc = (unsigned long) ksig->ka.sa.sa_handler;
+
+	DEBUGP("SIG deliver (%s:%d): sp=0x%p pc=0x%lx ra=0x%lx\n",
+	       current->comm, current->pid,
+	       frame, regs->csr_epc, regs->regs[1]);
+
+	return 0;
+}
+
+static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
+{
+	int ret;
+	sigset_t *oldset = sigmask_to_save();
+	void *vdso = current->mm->context.vdso;
+
+	/* Are we from a system call? */
+	if (regs->regs[0]) {
+		switch (regs->regs[4]) {
+		case -ERESTART_RESTARTBLOCK:
+		case -ERESTARTNOHAND:
+			regs->regs[4] = -EINTR;
+			break;
+		case -ERESTARTSYS:
+			if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
+				regs->regs[4] = -EINTR;
+				break;
+			}
+			fallthrough;
+		case -ERESTARTNOINTR:
+			regs->regs[4] = regs->orig_a0;
+			regs->csr_epc -= 4;
+		}
+
+		regs->regs[0] = 0;	/* Don't deal with this again.	*/
+	}
+
+	rseq_signal_deliver(ksig, regs);
+
+	ret = setup_rt_frame(vdso + current->thread.vdso->offset_sigreturn, ksig, regs, oldset);
+
+	signal_setup_done(ret, ksig, 0);
+}
+
+void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal)
+{
+	struct ksignal ksig;
+
+	if (has_signal && get_signal(&ksig)) {
+		/* Whee!  Actually deliver the signal.	*/
+		handle_signal(&ksig, regs);
+		return;
+	}
+
+	/* Are we from a system call? */
+	if (regs->regs[0]) {
+		switch (regs->regs[4]) {
+		case -ERESTARTNOHAND:
+		case -ERESTARTSYS:
+		case -ERESTARTNOINTR:
+			regs->regs[4] = regs->orig_a0;
+			regs->csr_epc -= 4;
+			break;
+
+		case -ERESTART_RESTARTBLOCK:
+			regs->regs[4] = regs->orig_a0;
+			regs->regs[11] = __NR_restart_syscall;
+			regs->csr_epc -= 4;
+			break;
+		}
+		regs->regs[0] = 0;	/* Don't deal with this again.	*/
+	}
+
+	/*
+	 * If there's no signal to deliver, we just put the saved sigmask
+	 * back
+	 */
+	restore_saved_sigmask();
+}
+
+static int signal_setup(void)
+{
+	if (cpu_has_fpu) {
+		save_fp_context = save_hw_fp_context;
+		restore_fp_context = restore_hw_fp_context;
+	} else {
+		save_fp_context = copy_fp_to_sigcontext;
+		restore_fp_context = copy_fp_from_sigcontext;
+	}
+
+	return 0;
+}
+
+arch_initcall(signal_setup);
-- 
2.27.0