LoongArch: Add signal handling support

Add ucontext/sigcontext definition and signal handling support for
LoongArch.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/uapi/asm/sigcontext.h

+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Author: Hanlu Li <lihanlu@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.cn>
+ *
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _UAPI_ASM_SIGCONTEXT_H
+#define _UAPI_ASM_SIGCONTEXT_H
+
+#include <linux/types.h>
+#include <linux/posix_types.h>
+
+/* FP context was used */
+#define SC_USED_FP		(1 << 0)
+/* Address error was due to memory load */
+#define SC_ADDRERR_RD		(1 << 30)
+/* Address error was due to memory store */
+#define SC_ADDRERR_WR		(1 << 31)
+
+struct sigcontext {
+	__u64	sc_pc;
+	__u64	sc_regs[32];
+	__u32	sc_flags;
+	__u64	sc_extcontext[0] __attribute__((__aligned__(16)));
+};
+
+#define CONTEXT_INFO_ALIGN	16
+struct sctx_info {
+	__u32	magic;
+	__u32	size;
+	__u64	padding;	/* padding to 16 bytes */
+};
+
+/* FPU context */
+#define FPU_CTX_MAGIC		0x46505501
+#define FPU_CTX_ALIGN		8
+struct fpu_context {
+	__u64	regs[32];
+	__u64	fcc;
+	__u32	fcsr;
+};
+
+#endif /* _UAPI_ASM_SIGCONTEXT_H */

arch/loongarch/include/uapi/asm/signal.h

+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _UAPI_ASM_SIGNAL_H
+#define _UAPI_ASM_SIGNAL_H
+
+#define MINSIGSTKSZ 4096
+#define SIGSTKSZ    16384
+
+#include <asm-generic/signal.h>
+
+#endif

arch/loongarch/include/uapi/asm/ucontext.h

+/* 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 */

arch/loongarch/kernel/signal.c

+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Author: Hanlu Li <lihanlu@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.cn>
+ * Copyright (C) 2020-2022 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 <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);
+
+struct rt_sigframe {
+	struct siginfo rs_info;
+	struct ucontext rs_uctx;
+};
+
+struct _ctx_layout {
+	struct sctx_info *addr;
+	unsigned int size;
+};
+
+struct extctx_layout {
+	unsigned long size;
+	unsigned int flags;
+	struct _ctx_layout fpu;
+	struct _ctx_layout end;
+};
+
+static void __user *get_ctx_through_ctxinfo(struct sctx_info *info)
+{
+	return (void __user *)((char *)info + sizeof(struct sctx_info));
+}
+
+/*
+ * 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_fpu_to_sigcontext(struct fpu_context __user *ctx)
+{
+	int i;
+	int err = 0;
+	uint64_t __user *regs	= (uint64_t *)&ctx->regs;
+	uint64_t __user *fcc	= &ctx->fcc;
+	uint32_t __user *fcsr	= &ctx->fcsr;
+
+	for (i = 0; i < NUM_FPU_REGS; i++) {
+		err |=
+		    __put_user(get_fpr64(&current->thread.fpu.fpr[i], 0),
+			       &regs[i]);
+	}
+	err |= __put_user(current->thread.fpu.fcc, fcc);
+	err |= __put_user(current->thread.fpu.fcsr, fcsr);
+
+	return err;
+}
+
+static int copy_fpu_from_sigcontext(struct fpu_context __user *ctx)
+{
+	int i;
+	int err = 0;
+	u64 fpr_val;
+	uint64_t __user *regs	= (uint64_t *)&ctx->regs;
+	uint64_t __user *fcc	= &ctx->fcc;
+	uint32_t __user *fcsr	= &ctx->fcsr;
+
+	for (i = 0; i < NUM_FPU_REGS; i++) {
+		err |= __get_user(fpr_val, &regs[i]);
+		set_fpr64(&current->thread.fpu.fpr[i], 0, fpr_val);
+	}
+	err |= __get_user(current->thread.fpu.fcc, fcc);
+	err |= __get_user(current->thread.fpu.fcsr, fcsr);
+
+	return err;
+}
+
+/*
+ * Wrappers for the assembly _{save,restore}_fp_context functions.
+ */
+static int save_hw_fpu_context(struct fpu_context __user *ctx)
+{
+	uint64_t __user *regs	= (uint64_t *)&ctx->regs;
+	uint64_t __user *fcc	= &ctx->fcc;
+	uint32_t __user *fcsr	= &ctx->fcsr;
+
+	return _save_fp_context(regs, fcc, fcsr);
+}
+
+static int restore_hw_fpu_context(struct fpu_context __user *ctx)
+{
+	uint64_t __user *regs	= (uint64_t *)&ctx->regs;
+	uint64_t __user *fcc	= &ctx->fcc;
+	uint32_t __user *fcsr	= &ctx->fcsr;
+
+	return _restore_fp_context(regs, fcc, fcsr);
+}
+
+static int fcsr_pending(unsigned int __user *fcsr)
+{
+	int err, sig = 0;
+	unsigned int csr, enabled;
+
+	err = __get_user(csr, fcsr);
+	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, fcsr);
+		sig = SIGFPE;
+	}
+	return err ?: sig;
+}
+
+/*
+ * Helper routines
+ */
+static int protected_save_fpu_context(struct extctx_layout *extctx)
+{
+	int err = 0;
+	struct sctx_info __user *info = extctx->fpu.addr;
+	struct fpu_context __user *fpu_ctx = (struct fpu_context *)get_ctx_through_ctxinfo(info);
+	uint64_t __user *regs	= (uint64_t *)&fpu_ctx->regs;
+	uint64_t __user *fcc	= &fpu_ctx->fcc;
+	uint32_t __user *fcsr	= &fpu_ctx->fcsr;
+
+	while (1) {
+		lock_fpu_owner();
+		if (is_fpu_owner())
+			err = save_hw_fpu_context(fpu_ctx);
+		else
+			err = copy_fpu_to_sigcontext(fpu_ctx);
+		unlock_fpu_owner();
+
+		err |= __put_user(FPU_CTX_MAGIC, &info->magic);
+		err |= __put_user(extctx->fpu.size, &info->size);
+
+		if (likely(!err))
+			break;
+		/* Touch the FPU context and try again */
+		err = __put_user(0, &regs[0]) |
+			__put_user(0, &regs[31]) |
+			__put_user(0, fcc) |
+			__put_user(0, fcsr);
+		if (err)
+			return err;	/* really bad sigcontext */
+	}
+
+	return err;
+}
+
+static int protected_restore_fpu_context(struct extctx_layout *extctx)
+{
+	int err = 0, sig = 0, tmp __maybe_unused;
+	struct sctx_info __user *info = extctx->fpu.addr;
+	struct fpu_context __user *fpu_ctx = (struct fpu_context *)get_ctx_through_ctxinfo(info);
+	uint64_t __user *regs	= (uint64_t *)&fpu_ctx->regs;
+	uint64_t __user *fcc	= &fpu_ctx->fcc;
+	uint32_t __user *fcsr	= &fpu_ctx->fcsr;
+
+	err = sig = fcsr_pending(fcsr);
+	if (err < 0)
+		return err;
+
+	while (1) {
+		lock_fpu_owner();
+		if (is_fpu_owner())
+			err = restore_hw_fpu_context(fpu_ctx);
+		else
+			err = copy_fpu_from_sigcontext(fpu_ctx);
+		unlock_fpu_owner();
+
+		if (likely(!err))
+			break;
+		/* Touch the FPU context and try again */
+		err = __get_user(tmp, &regs[0]) |
+			__get_user(tmp, &regs[31]) |
+			__get_user(tmp, fcc) |
+			__get_user(tmp, fcsr);
+		if (err)
+			break;	/* really bad sigcontext */
+	}
+
+	return err ?: sig;
+}
+
+static int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
+			    struct extctx_layout *extctx)
+{
+	int i, err = 0;
+	struct sctx_info __user *info;
+
+	err |= __put_user(regs->csr_era, &sc->sc_pc);
+	err |= __put_user(extctx->flags, &sc->sc_flags);
+
+	err |= __put_user(0, &sc->sc_regs[0]);
+	for (i = 1; i < 32; i++)
+		err |= __put_user(regs->regs[i], &sc->sc_regs[i]);
+
+	if (extctx->fpu.addr)
+		err |= protected_save_fpu_context(extctx);
+
+	/* Set the "end" magic */
+	info = (struct sctx_info *)extctx->end.addr;
+	err |= __put_user(0, &info->magic);
+	err |= __put_user(0, &info->size);
+
+	return err;
+}
+
+static int parse_extcontext(struct sigcontext __user *sc, struct extctx_layout *extctx)
+{
+	int err = 0;
+	unsigned int magic, size;
+	struct sctx_info __user *info = (struct sctx_info __user *)&sc->sc_extcontext;
+
+	while(1) {
+		err |= __get_user(magic, &info->magic);
+		err |= __get_user(size, &info->size);
+		if (err)
+			return err;
+
+		switch (magic) {
+		case 0: /* END */
+			goto done;
+
+		case FPU_CTX_MAGIC:
+			if (size < (sizeof(struct sctx_info) +
+				    sizeof(struct fpu_context)))
+				goto invalid;
+			extctx->fpu.addr = info;
+			break;
+
+		default:
+			goto invalid;
+		}
+
+		info = (struct sctx_info *)((char *)info + size);
+	}
+
+done:
+	return 0;
+
+invalid:
+	return -EINVAL;
+}
+
+static int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
+{
+	int i, err = 0;
+	struct extctx_layout extctx;
+
+	memset(&extctx, 0, sizeof(struct extctx_layout));
+
+	err = __get_user(extctx.flags, &sc->sc_flags);
+	if (err)
+		goto bad;
+
+	err = parse_extcontext(sc, &extctx);
+	if (err)
+		goto bad;
+
+	conditional_used_math(extctx.flags & SC_USED_FP);
+
+	/*
+	 * The signal handler may have used FPU; give it up if the program
+	 * doesn't want it following sigreturn.
+	 */
+	if (!(extctx.flags & SC_USED_FP))
+		lose_fpu(0);
+
+	/* Always make any pending restarted system calls return -EINTR */
+	current->restart_block.fn = do_no_restart_syscall;
+
+	err |= __get_user(regs->csr_era, &sc->sc_pc);
+	for (i = 1; i < 32; i++)
+		err |= __get_user(regs->regs[i], &sc->sc_regs[i]);
+
+	if (extctx.fpu.addr)
+		err |= protected_restore_fpu_context(&extctx);
+
+bad:
+	return err;
+}
+
+static unsigned int handle_flags(void)
+{
+	unsigned int flags = 0;
+
+	flags = used_math() ? SC_USED_FP : 0;
+
+	switch (current->thread.error_code) {
+	case 1:
+		flags |= SC_ADDRERR_RD;
+		break;
+	case 2:
+		flags |= SC_ADDRERR_WR;
+		break;
+	}
+
+	return flags;
+}
+
+static unsigned long extframe_alloc(struct extctx_layout *extctx,
+				    struct _ctx_layout *layout,
+				    size_t size, unsigned int align, unsigned long base)
+{
+	unsigned long new_base = base - size;
+
+	new_base = round_down(new_base, (align < 16 ? 16 : align));
+	new_base -= sizeof(struct sctx_info);
+
+	layout->addr = (void *)new_base;
+	layout->size = (unsigned int)(base - new_base);
+	extctx->size += layout->size;
+
+	return new_base;
+}
+
+static unsigned long setup_extcontext(struct extctx_layout *extctx, unsigned long sp)
+{
+	unsigned long new_sp = sp;
+
+	memset(extctx, 0, sizeof(struct extctx_layout));
+
+	extctx->flags = handle_flags();
+
+	/* Grow down, alloc "end" context info first. */
+	new_sp -= sizeof(struct sctx_info);
+	extctx->end.addr = (void *)new_sp;
+	extctx->end.size = (unsigned int)sizeof(struct sctx_info);
+	extctx->size += extctx->end.size;
+
+	if (extctx->flags & SC_USED_FP) {
+		if (cpu_has_fpu)
+			new_sp = extframe_alloc(extctx, &extctx->fpu,
+			  sizeof(struct fpu_context), FPU_CTX_ALIGN, new_sp);
+	}
+
+	return new_sp;
+}
+
+void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
+			  struct extctx_layout *extctx)
+{
+	unsigned long sp;
+
+	/* Default to using normal stack */
+	sp = regs->regs[3];
+
+	/*
+	 * If we are on the alternate signal stack and would overflow it, don't.
+	 * Return an always-bogus address instead so we will die with SIGSEGV.
+	 */
+	if (on_sig_stack(sp) &&
+	    !likely(on_sig_stack(sp - sizeof(struct rt_sigframe))))
+		return (void __user __force *)(-1UL);
+
+	sp = sigsp(sp, ksig);
+	sp = round_down(sp, 16);
+	sp = setup_extcontext(extctx, sp);
+	sp -= sizeof(struct rt_sigframe);
+
+	if (!IS_ALIGNED(sp, 16))
+		BUG();
+
+	return (void __user *)sp;
+}
+
+/*
+ * 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);
+
+	regs->regs[0] = 0; /* No syscall restarting */
+	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 extctx_layout extctx;
+	struct rt_sigframe __user *frame;
+
+	frame = get_sigframe(ksig, regs, &extctx);
+	if (!access_ok(frame, sizeof(*frame) + extctx.size))
+		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, &extctx);
+	err |= __copy_to_user(&frame->rs_uctx.uc_sigmask, set, sizeof(*set));
+
+	if (err)
+		return -EFAULT;
+
+	/*
+	 * Arguments to signal handler:
+	 *
+	 *   a0 = signal number
+	 *   a1 = pointer to siginfo
+	 *   a2 = pointer to ucontext
+	 *
+	 * c0_era point to the signal handler, $r3 (sp) 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_era = (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_era, 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_era -= 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_era -= 4;
+			break;
+
+		case -ERESTART_RESTARTBLOCK:
+			regs->regs[4] = regs->orig_a0;
+			regs->regs[11] = __NR_restart_syscall;
+			regs->csr_era -= 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();
+}