Add a uptr_t type that can hold a pointer to either a user or kernel
memory region, and simply helpers to copy to and from it. For
architectures like x86 that have non-overlapping user and kernel
address space it just is a union and uses a TASK_SIZE check to
select the proper copy routine. For architectures with overlapping
address spaces a flag to indicate the address space is used instead.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
include/linux/sockptr.h | 121 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 121 insertions(+)
create mode 100644 include/linux/sockptr.h
diff --git a/include/linux/sockptr.h b/include/linux/sockptr.h
new file mode 100644
index 00000000000000..e41dfa52555dec
--- /dev/null
+++ b/include/linux/sockptr.h
@@ -0,0 +1,121 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2020 Christoph Hellwig.
+ *
+ * Support for "universal" pointers that can point to either kernel or userspace
+ * memory.
+ */
+#ifndef _LINUX_SOCKPTR_H
+#define _LINUX_SOCKPTR_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 };
+}
+#else /* CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE */
+typedef struct {
+ union {
+ void *kernel;
+ void __user *user;
+ };
+ bool is_kernel : 1;
+} sockptr_t;
+
+static inline bool sockptr_is_kernel(sockptr_t sockptr)
+{
+ return sockptr.is_kernel;
+}
+
+static inline sockptr_t KERNEL_SOCKPTR(void *p)
+{
+ return (sockptr_t) { .kernel = p, .is_kernel = true };
+}
+#endif /* CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE */
+
+static inline sockptr_t USER_SOCKPTR(void __user *p)
+{
+ return (sockptr_t) { .user = p };
+}
+
+static inline bool sockptr_is_null(sockptr_t sockptr)
+{
+ return !sockptr.user && !sockptr.kernel;
+}
+
+static inline int copy_from_sockptr(void *dst, sockptr_t src, size_t size)
+{
+ if (!sockptr_is_kernel(src))
+ return copy_from_user(dst, src.user, size);
+ memcpy(dst, src.kernel, size);
+ return 0;
+}
+
+static inline int copy_to_sockptr(sockptr_t dst, const void *src, size_t size)
+{
+ if (!sockptr_is_kernel(dst))
+ return copy_to_user(dst.user, src, size);
+ memcpy(dst.kernel, src, size);
+ return 0;
+}
+
+static inline void *memdup_sockptr(sockptr_t src, size_t len)
+{
+ void *p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN);
+
+ if (!p)
+ return ERR_PTR(-ENOMEM);
+ if (copy_from_sockptr(p, src, len)) {
+ kfree(p);
+ return ERR_PTR(-EFAULT);
+ }
+ return p;
+}
+
+static inline void *memdup_sockptr_nul(sockptr_t src, size_t len)
+{
+ char *p = kmalloc_track_caller(len + 1, GFP_KERNEL);
+
+ if (!p)
+ return ERR_PTR(-ENOMEM);
+ if (copy_from_sockptr(p, src, len)) {
+ kfree(p);
+ return ERR_PTR(-EFAULT);
+ }
+ p[len] = '\0';
+ return p;
+}
+
+static inline void sockptr_advance(sockptr_t sockptr, size_t len)
+{
+ if (sockptr_is_kernel(sockptr))
+ sockptr.kernel += len;
+ else
+ sockptr.user += len;
+}
+
+static inline long strncpy_from_sockptr(char *dst, sockptr_t src, size_t count)
+{
+ if (sockptr_is_kernel(src)) {
+ size_t len = min(strnlen(src.kernel, count - 1) + 1, count);
+
+ memcpy(dst, src.kernel, len);
+ return len;
+ }
+ return strncpy_from_user(dst, src.user, count);
+}
+
+#endif /* _LINUX_SOCKPTR_H */
--
2.27.0
