arm64: System calls handling

This patch adds support for system calls coming from 64-bit
applications. It uses the asm-generic/unistd.h definitions with the
canonical set of system calls. The private system calls are only used
for 32-bit (compat) applications as 64-bit ones can set the TLS and
flush the caches entirely from user space.

The sys_call_table is just an array defined in a C file and it contains
pointers to the syscall functions. The array is 4KB aligned to allow the
use of the ADRP instruction (longer range ADR) in entry.S.
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/stat.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_STAT_H
+#define __ASM_STAT_H
+
+#include <asm-generic/stat.h>
+
+#if defined(__KERNEL__) && defined(CONFIG_COMPAT)
+
+#include <asm/compat.h>
+
+/*
+ * struct stat64 is needed for compat tasks only. Its definition is different
+ * from the generic struct stat64.
+ */
+struct stat64 {
+	compat_u64	st_dev;
+	unsigned char   __pad0[4];
+
+#define STAT64_HAS_BROKEN_ST_INO	1
+	compat_ulong_t	__st_ino;
+	compat_uint_t	st_mode;
+	compat_uint_t	st_nlink;
+
+	compat_ulong_t	st_uid;
+	compat_ulong_t	st_gid;
+
+	compat_u64	st_rdev;
+	unsigned char   __pad3[4];
+
+	compat_s64	st_size;
+	compat_ulong_t	st_blksize;
+	compat_u64	st_blocks;	/* Number of 512-byte blocks allocated. */
+
+	compat_ulong_t	st_atime;
+	compat_ulong_t	st_atime_nsec;
+
+	compat_ulong_t	st_mtime;
+	compat_ulong_t	st_mtime_nsec;
+
+	compat_ulong_t	st_ctime;
+	compat_ulong_t	st_ctime_nsec;
+
+	compat_u64	st_ino;
+};
+
+#endif
+
+#endif

arch/arm64/include/asm/statfs.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_STATFS_H
+#define __ASM_STATFS_H
+
+#define ARCH_PACK_COMPAT_STATFS64 __attribute__((packed,aligned(4)))
+
+#include <asm-generic/statfs.h>
+
+#endif

arch/arm64/include/asm/syscalls.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_SYSCALLS_H
+#define __ASM_SYSCALLS_H
+
+#include <linux/linkage.h>
+#include <linux/compiler.h>
+#include <linux/signal.h>
+
+/*
+ * System call wrappers implemented in kernel/entry.S.
+ */
+asmlinkage long sys_execve_wrapper(const char __user *filename,
+				   const char __user *const __user *argv,
+				   const char __user *const __user *envp);
+asmlinkage long sys_clone_wrapper(unsigned long clone_flags,
+				  unsigned long newsp,
+				  void __user *parent_tid,
+				  unsigned long tls_val,
+				  void __user *child_tid);
+asmlinkage long sys_rt_sigreturn_wrapper(void);
+asmlinkage long sys_sigaltstack_wrapper(const stack_t __user *uss,
+					stack_t __user *uoss);
+
+#include <asm-generic/syscalls.h>
+
+#endif	/* __ASM_SYSCALLS_H */

arch/arm64/include/asm/unistd.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/>.
+ */
+#if !defined(__ASM_UNISTD_H) || defined(__SYSCALL)
+#define __ASM_UNISTD_H
+
+#ifndef __SYSCALL_COMPAT
+#include <asm-generic/unistd.h>
+#endif
+
+#if defined(__KERNEL__) && defined(CONFIG_COMPAT)
+#include <asm/unistd32.h>
+#endif
+
+#endif /* __ASM_UNISTD_H */

arch/arm64/kernel/sys.c

+/*
+ * AArch64-specific system calls implementation
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ *
+ * 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/compiler.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/export.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/syscalls.h>
+
+/*
+ * Clone a task - this clones the calling program thread.
+ */
+asmlinkage long sys_clone(unsigned long clone_flags, unsigned long newsp,
+			  int __user *parent_tidptr, unsigned long tls_val,
+			  int __user *child_tidptr, struct pt_regs *regs)
+{
+	if (!newsp)
+		newsp = regs->sp;
+	/* 16-byte aligned stack mandatory on AArch64 */
+	if (newsp & 15)
+		return -EINVAL;
+	return do_fork(clone_flags, newsp, regs, 0, parent_tidptr, child_tidptr);
+}
+
+/*
+ * sys_execve() executes a new program.
+ */
+asmlinkage long sys_execve(const char __user *filenamei,
+			   const char __user *const __user *argv,
+			   const char __user *const __user *envp,
+			   struct pt_regs *regs)
+{
+	long error;
+	char * filename;
+
+	filename = getname(filenamei);
+	error = PTR_ERR(filename);
+	if (IS_ERR(filename))
+		goto out;
+	error = do_execve(filename, argv, envp, regs);
+	putname(filename);
+out:
+	return error;
+}
+
+int kernel_execve(const char *filename,
+		  const char *const argv[],
+		  const char *const envp[])
+{
+	struct pt_regs regs;
+	int ret;
+
+	memset(&regs, 0, sizeof(struct pt_regs));
+	ret = do_execve(filename,
+			(const char __user *const __user *)argv,
+			(const char __user *const __user *)envp, &regs);
+	if (ret < 0)
+		goto out;
+
+	/*
+	 * Save argc to the register structure for userspace.
+	 */
+	regs.regs[0] = ret;
+
+	/*
+	 * We were successful.  We won't be returning to our caller, but
+	 * instead to user space by manipulating the kernel stack.
+	 */
+	asm(	"add	x0, %0, %1\n\t"
+		"mov	x1, %2\n\t"
+		"mov	x2, %3\n\t"
+		"bl	memmove\n\t"	/* copy regs to top of stack */
+		"mov	x27, #0\n\t"	/* not a syscall */
+		"mov	x28, %0\n\t"	/* thread structure */
+		"mov	sp, x0\n\t"	/* reposition stack pointer */
+		"b	ret_to_user"
+		:
+		: "r" (current_thread_info()),
+		  "Ir" (THREAD_START_SP - sizeof(regs)),
+		  "r" (&regs),
+		  "Ir" (sizeof(regs))
+		: "x0", "x1", "x2", "x27", "x28", "x30", "memory");
+
+ out:
+	return ret;
+}
+EXPORT_SYMBOL(kernel_execve);
+
+asmlinkage long sys_mmap(unsigned long addr, unsigned long len,
+			 unsigned long prot, unsigned long flags,
+			 unsigned long fd, off_t off)
+{
+	if (offset_in_page(off) != 0)
+		return -EINVAL;
+
+	return sys_mmap_pgoff(addr, len, prot, flags, fd, off >> PAGE_SHIFT);
+}
+
+/*
+ * Wrappers to pass the pt_regs argument.
+ */
+#define sys_execve		sys_execve_wrapper
+#define sys_clone		sys_clone_wrapper
+#define sys_rt_sigreturn	sys_rt_sigreturn_wrapper
+#define sys_sigaltstack		sys_sigaltstack_wrapper
+
+#include <asm/syscalls.h>
+
+#undef __SYSCALL
+#define __SYSCALL(nr, sym)	[nr] = sym,
+
+/*
+ * The sys_call_table array must be 4K aligned to be accessible from
+ * kernel/entry.S.
+ */
+void *sys_call_table[__NR_syscalls] __aligned(4096) = {
+	[0 ... __NR_syscalls - 1] = sys_ni_syscall,
+#include <asm/unistd.h>
+};