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authorChristoph Hellwig <hch@lst.de>2020-05-30 14:51:11 +1000
committerStephen Rothwell <sfr@canb.auug.org.au>2020-06-02 19:15:38 +1000
commit1bd480b1716ca793aa02a66353c11c3406b05fd3 (patch)
tree8316d147103d3e1b50fb9e2cdcc3dbdefe92dd02
parentebf4c9a0c001d4362b83b14878aeb7e8801aa925 (diff)
downloadlinux-1bd480b1716ca793aa02a66353c11c3406b05fd3.tar.gz
maccess: clarify kerneldoc comments
Add proper kerneldoc comments for probe_kernel_read_strict and probe_kernel_read strncpy_from_unsafe_strict and explain the different versus the non-strict version. Link: http://lkml.kernel.org/r/20200521152301.2587579-5-hch@lst.de Signed-off-by: Christoph Hellwig <hch@lst.de> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
-rw-r--r--mm/maccess.c60
1 files changed, 43 insertions, 17 deletions
diff --git a/mm/maccess.c b/mm/maccess.c
index 773e14f7d140..9867bbaa9967 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -31,29 +31,36 @@ probe_write_common(void __user *dst, const void *src, size_t size)
}
/**
- * probe_kernel_read(): safely attempt to read from a kernel-space location
+ * probe_kernel_read(): safely attempt to read from any location
* @dst: pointer to the buffer that shall take the data
* @src: address to read from
* @size: size of the data chunk
*
- * Safely read from address @src to the buffer at @dst. If a kernel fault
- * happens, handle that and return -EFAULT.
+ * Same as probe_kernel_read_strict() except that for architectures with
+ * not fully separated user and kernel address spaces this function also works
+ * for user address tanges.
+ *
+ * DO NOT USE THIS FUNCTION - it is broken on architectures with entirely
+ * separate kernel and user address spaces, and also a bad idea otherwise.
+ */
+long __weak probe_kernel_read(void *dst, const void *src, size_t size)
+ __attribute__((alias("__probe_kernel_read")));
+
+/**
+ * probe_kernel_read_strict(): safely attempt to read from kernel-space
+ * @dst: pointer to the buffer that shall take the data
+ * @src: address to read from
+ * @size: size of the data chunk
+ *
+ * Safely read from kernel address @src to the buffer at @dst. If a kernel
+ * fault happens, handle that and return -EFAULT.
*
* We ensure that the copy_from_user is executed in atomic context so that
* do_page_fault() doesn't attempt to take mmap_lock. This makes
* probe_kernel_read() suitable for use within regions where the caller
* already holds mmap_lock, or other locks which nest inside mmap_lock.
- *
- * probe_kernel_read_strict() is the same as probe_kernel_read() except for
- * the case where architectures have non-overlapping user and kernel address
- * ranges: probe_kernel_read_strict() will additionally return -EFAULT for
- * probing memory on a user address range where probe_user_read() is supposed
- * to be used instead.
*/
-long __weak probe_kernel_read(void *dst, const void *src, size_t size)
- __attribute__((alias("__probe_kernel_read")));
-
long __weak probe_kernel_read_strict(void *dst, const void *src, size_t size)
__attribute__((alias("__probe_kernel_read")));
@@ -153,15 +160,34 @@ long probe_user_write(void __user *dst, const void *src, size_t size)
* If @count is smaller than the length of the string, copies @count-1 bytes,
* sets the last byte of @dst buffer to NUL and returns @count.
*
- * strncpy_from_unsafe_strict() is the same as strncpy_from_unsafe() except
- * for the case where architectures have non-overlapping user and kernel address
- * ranges: strncpy_from_unsafe_strict() will additionally return -EFAULT for
- * probing memory on a user address range where strncpy_from_unsafe_user() is
- * supposed to be used instead.
+ * Same as strncpy_from_unsafe_strict() except that for architectures with
+ * not fully separated user and kernel address spaces this function also works
+ * for user address tanges.
+ *
+ * DO NOT USE THIS FUNCTION - it is broken on architectures with entirely
+ * separate kernel and user address spaces, and also a bad idea otherwise.
*/
long __weak strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
__attribute__((alias("__strncpy_from_unsafe")));
+/**
+ * strncpy_from_unsafe_strict: - Copy a NUL terminated string from unsafe
+ * address.
+ * @dst: Destination address, in kernel space. This buffer must be at
+ * least @count bytes long.
+ * @unsafe_addr: Unsafe address.
+ * @count: Maximum number of bytes to copy, including the trailing NUL.
+ *
+ * Copies a NUL-terminated string from unsafe address to kernel buffer.
+ *
+ * On success, returns the length of the string INCLUDING the trailing NUL.
+ *
+ * If access fails, returns -EFAULT (some data may have been copied
+ * and the trailing NUL added).
+ *
+ * If @count is smaller than the length of the string, copies @count-1 bytes,
+ * sets the last byte of @dst buffer to NUL and returns @count.
+ */
long __weak strncpy_from_unsafe_strict(char *dst, const void *unsafe_addr,
long count)
__attribute__((alias("__strncpy_from_unsafe")));