net: optimize the sockptr_t for unified kernel/user address spaces

For architectures like x86 and arm64 we don't need the separate bit to
indicate that a pointer is a kernel pointer as the address spaces are
unified.  That way the sockptr_t can be reduced to a union of two
pointers, which leads to nicer calling conventions.

The only caveat is that we need to check that users don't pass in kernel
address and thus gain access to kernel memory.  Thus the USER_SOCKPTR
helper is replaced with a init_user_sockptr function that does this check
and returns an error if it fails.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/sockptr.h

@@ -8,9 +8,34 @@
 #ifndef _LINUX_SOCKPTR_H
 #define _LINUX_SOCKPTR_H
 
+#include <linux/compiler.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 
+#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
+typedef union {
+	void		*kernel;
+	void __user	*user;
+} sockptr_t;
+
+static inline bool sockptr_is_kernel(sockptr_t sockptr)
+{
+	return (unsigned long)sockptr.kernel >= TASK_SIZE;
+}
+
+static inline sockptr_t KERNEL_SOCKPTR(void *p)
+{
+	return (sockptr_t) { .kernel = p };
+}
+
+static inline int __must_check init_user_sockptr(sockptr_t *sp, void __user *p)
+{
+	if ((unsigned long)p >= TASK_SIZE)
+		return -EFAULT;
+	sp->user = p;
+	return 0;
+}
+#else /* CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE */
 typedef struct {
 	union {
 		void		*kernel;
@@ -29,10 +54,13 @@ static inline sockptr_t KERNEL_SOCKPTR(void *p)
 	return (sockptr_t) { .kernel = p, .is_kernel = true };
 }
 
-static inline sockptr_t USER_SOCKPTR(void __user *p)
+static inline int __must_check init_user_sockptr(sockptr_t *sp, void __user *p)
 {
-	return (sockptr_t) { .user = p };
+	sp->user = p;
+	sp->is_kernel = false;
+	return 0;
 }
+#endif /* CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE */
 
 static inline bool sockptr_is_null(sockptr_t sockptr)
 {

net/ipv4/bpfilter/sockopt.c

@@ -57,16 +57,18 @@ int bpfilter_ip_set_sockopt(struct sock *sk, int optname, sockptr_t optval,
 	return bpfilter_mbox_request(sk, optname, optval, optlen, true);
 }
 
-int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval,
-			    int __user *optlen)
+int bpfilter_ip_get_sockopt(struct sock *sk, int optname,
+			    char __user *user_optval, int __user *optlen)
 {
-	int len;
+	sockptr_t optval;
+	int err, len;
 
 	if (get_user(len, optlen))
 		return -EFAULT;
-
-	return bpfilter_mbox_request(sk, optname, USER_SOCKPTR(optval), len,
-				     false);
+	err = init_user_sockptr(&optval, user_optval);
+	if (err)
+		return err;
+	return bpfilter_mbox_request(sk, optname, optval, len, false);
 }
 
 static int __init bpfilter_sockopt_init(void)

net/socket.c

@@ -2097,14 +2097,18 @@ static bool sock_use_custom_sol_socket(const struct socket *sock)
 int __sys_setsockopt(int fd, int level, int optname, char __user *user_optval,
 		int optlen)
 {
-	sockptr_t optval = USER_SOCKPTR(user_optval);
+	sockptr_t optval;
 	char *kernel_optval = NULL;
 	int err, fput_needed;
 	struct socket *sock;
 
 	if (optlen < 0)
 		return -EINVAL;
 
+	err = init_user_sockptr(&optval, user_optval);
+	if (err)
+		return err;
+
 	sock = sockfd_lookup_light(fd, &err, &fput_needed);
 	if (!sock)
 		return err;