Merge v7.1.4linux-rolling-stable

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 27 deletions

diff --git a/Documentation/crypto/userspace-if.rst b/Documentation/crypto/userspace-if.rst
index 021759198fe7..d220e266b8de 100644
--- a/Documentation/crypto/userspace-if.rst
+++ b/Documentation/crypto/userspace-if.rst
@@ -327,33 +327,10 @@ CRYPTO_USER_API_RNG_CAVP option:
 Zero-Copy Interface
 -------------------
 
-In addition to the send/write/read/recv system call family, the AF_ALG
-interface can be accessed with the zero-copy interface of
-splice/vmsplice. As the name indicates, the kernel tries to avoid a copy
-operation into kernel space.
-
-The zero-copy operation requires data to be aligned at the page
-boundary. Non-aligned data can be used as well, but may require more
-operations of the kernel which would defeat the speed gains obtained
-from the zero-copy interface.
-
-The system-inherent limit for the size of one zero-copy operation is 16
-pages. If more data is to be sent to AF_ALG, user space must slice the
-input into segments with a maximum size of 16 pages.
-
-Zero-copy can be used with the following code example (a complete
-working example is provided with libkcapi):
-
-::
-
-    int pipes[2];
-
-    pipe(pipes);
-    /* input data in iov */
-    vmsplice(pipes[1], iov, iovlen, SPLICE_F_GIFT);
-    /* opfd is the file descriptor returned from accept() system call */
-    splice(pipes[0], NULL, opfd, NULL, ret, 0);
-    read(opfd, out, outlen);
+AF_ALG used to have zero-copy support, but it was removed due to it being a
+frequent source of vulnerabilities.  For backwards compatibility the splice()
+and sendfile() system calls are still supported, but the kernel will make an
+internal copy of the data before passing it to the crypto code.
 
 
 Setsockopt Interface