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    Subject[PATCH 04/20] maccess: clarify kerneldoc comments
    Date
    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.

    Signed-off-by: Christoph Hellwig <hch@lst.de>
    ---
    mm/maccess.c | 61 ++++++++++++++++++++++++++++++++++++----------------
    1 file changed, 43 insertions(+), 18 deletions(-)

    diff --git a/mm/maccess.c b/mm/maccess.c
    index 4e7f3b6eb05ae..747581ac50dc9 100644
    --- a/mm/maccess.c
    +++ b/mm/maccess.c
    @@ -31,29 +31,35 @@ 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_sem. This makes
    * probe_kernel_read() suitable for use within regions where the caller
    * already holds mmap_sem, or other locks which nest inside mmap_sem.
    - *
    - * 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 +159,34 @@ 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")));
    --
    2.26.2
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