libc/string: add memcpy_from_ci()

This adds memcpy_from_ci, a cache inhibited version of memcpy, required
by secure boot. The secure boot verification code is stored in a secure
ROM and the logic that contains the ROM within the processor is
implemented in a way that it only responds to CI (cache inhibited)
operations. Due to performance issues we copy the verification code from
the secure ROM to RAM and we use memcpy_ci for that.

What makes memcpy_ci vs ordinary memcpy?

memcpy copies data like in the example below and the compiler translates that
to load instructions that are not cache inhibited (e.g. lbzx - load byte and
zero indexed). In other words, the data is cached.

a[i] = b[i]

memcpy_ci copies data using the cache inhibited version of load instructions:
in_8() and in_be32(), both defined in include/io.h. These functions use lbzcix
and lwzcix assembly instructions, respectively. In this case, the data is not
cached as required by the logic that contains the ROM.

*((uint8_t*) destp) = in_8((uint8_t*)srcp);
*((uint32_t*) destp) = in_be32((uint32_t*)srcp)

Signed-off-by: Claudio Carvalho <cclaudio@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

2 files changed, 52 insertions, 4 deletions

diff --git a/libc/string/Makefile.inc b/libc/string/Makefile.inc
index 3b7c8ce..fb2f037 100644
--- a/libc/string/Makefile.inc
+++ b/libc/string/Makefile.inc
@@ -1,5 +1,5 @@
 # *****************************************************************************
-# * Copyright (c) 2004, 2008 IBM Corporation
+# * Copyright (c) 2004, 2016 IBM Corporation
 # * All rights reserved.
 # * This program and the accompanying materials
 # * are made available under the terms of the BSD License
@@ -12,9 +12,10 @@
 
 SUBDIRS += $(LIBCDIR)/string
 
-STRING_OBJS = strcat.o strchr.o strcmp.o strcpy.o strlen.o strncmp.o \
-	      strncpy.o strstr.o memset.o memcpy.o memmove.o memchr.o \
-	      memcmp.o strcasecmp.o strncasecmp.o strtok.o strdup.o
+STRING_OBJS = strcat.o strchr.o strcmp.o strcpy.o strlen.o \
+	      strncmp.o strncpy.o strstr.o memset.o memcpy.o memcpy_from_ci.o \
+	      memmove.o memchr.o memcmp.o strcasecmp.o strncasecmp.o \
+	      strtok.o strdup.o
 STRING = $(LIBCDIR)/string/built-in.o
 $(STRING): $(STRING_OBJS:%=$(LIBCDIR)/string/%)
 
diff --git a/libc/string/memcpy_from_ci.c b/libc/string/memcpy_from_ci.c
new file mode 100644
index 0000000..02affa3
--- /dev/null
+++ b/libc/string/memcpy_from_ci.c
@@ -0,0 +1,47 @@
+/* Copyright 2013-2016 IBM Corp
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+ * implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <string.h>
+#include <ccan/short_types/short_types.h>
+#include <io.h>
+
+void* memcpy_from_ci(void *destpp, const void *srcpp, size_t len)
+{
+	const size_t block = sizeof(uint64_t);
+	unsigned long int destp = (long int) destpp;
+	unsigned long int srcp = (long int) srcpp;
+
+	/* Copy as many blocks as possible if srcp is block aligned */
+	if ((srcp % block) == 0) {
+		while ((len - block) > -1) {
+			*((uint64_t*) destp) = in_be64((uint64_t*)srcp);
+			srcp += block;
+			destp += block;
+			len -= block;
+		}
+	}
+	/*
+	 * Byte-by-byte copy if srcp is not block aligned or len is/becomes
+	 * less than one block
+	 */
+	while (len > 0) {
+		*((uint8_t*) destp) = in_8((uint8_t*)srcp);
+		srcp += 1;
+		destp += 1;
+		len--;
+	}
+	return destpp;
+}