mm, treewide: rename kzfree() to kfree_sensitive()

As said by Linus:

  A symmetric naming is only helpful if it implies symmetries in use.
  Otherwise it's actively misleading.

  In "kzalloc()", the z is meaningful and an important part of what the
  caller wants.

  In "kzfree()", the z is actively detrimental, because maybe in the
  future we really _might_ want to use that "memfill(0xdeadbeef)" or
  something. The "zero" part of the interface isn't even _relevant_.

The main reason that kzfree() exists is to clear sensitive information
that should not be leaked to other future users of the same memory
objects.

Rename kzfree() to kfree_sensitive() to follow the example of the recently
added kvfree_sensitive() and make the intention of the API more explicit.
In addition, memzero_explicit() is used to clear the memory to make sure
that it won't get optimized away by the compiler.

The renaming is done by using the command sequence:

  git grep -w --name-only kzfree |\
  xargs sed -i 's/kzfree/kfree_sensitive/'

followed by some editing of the kfree_sensitive() kerneldoc and adding
a kzfree backward compatibility macro in slab.h.

[akpm@linux-foundation.org: fs/crypto/inline_crypt.c needs linux/slab.h]
[akpm@linux-foundation.org: fix fs/crypto/inline_crypt.c some more]

Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Joe Perches <joe@perches.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: "Jason A . Donenfeld" <Jason@zx2c4.com>
Link: http://lkml.kernel.org/r/20200616154311.12314-3-longman@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/crypto/ccree/cc_cipher.c

@@ -257,7 +257,7 @@ static void cc_cipher_exit(struct crypto_tfm *tfm)
 		&ctx_p->user.key_dma_addr);
 
 	/* Free key buffer in context */
-	kzfree(ctx_p->user.key);
+	kfree_sensitive(ctx_p->user.key);
 	dev_dbg(dev, "Free key buffer in context. key=@%p\n", ctx_p->user.key);
 }
 
@@ -881,7 +881,7 @@ static void cc_cipher_complete(struct device *dev, void *cc_req, int err)
 		/* Not a BACKLOG notification */
 		cc_unmap_cipher_request(dev, req_ctx, ivsize, src, dst);
 		memcpy(req->iv, req_ctx->iv, ivsize);
-		kzfree(req_ctx->iv);
+		kfree_sensitive(req_ctx->iv);
 	}
 
 	skcipher_request_complete(req, err);
@@ -994,7 +994,7 @@ static int cc_cipher_process(struct skcipher_request *req,
 
 exit_process:
 	if (rc != -EINPROGRESS && rc != -EBUSY) {
-		kzfree(req_ctx->iv);
+		kfree_sensitive(req_ctx->iv);
 	}
 
 	return rc;