malloc: Basic support for memory tagging in the malloc() family

This patch adds the basic support for memory tagging.

Various flavours are supported, particularly being able to turn on
tagged memory at run-time: this allows the same code to be used on
systems where memory tagging support is not present without neededing
a separate build of glibc.  Also, depending on whether the kernel
supports it, the code will use mmap for the default arena if morecore
does not, or cannot support tagged memory (on AArch64 it is not
available).

All the hooks use function pointers to allow this to work without
needing ifuncs.

Reviewed-by: DJ Delorie <dj@redhat.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/sysdeps/generic/libc-mtag.h b/sysdeps/generic/libc-mtag.h
new file mode 100644
index 0000000000..07f0203253
--- /dev/null
+++ b/sysdeps/generic/libc-mtag.h
@@ -0,0 +1,52 @@
+/* libc-internal interface for tagged (colored) memory support.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _GENERIC_LIBC_MTAG_H
+#define _GENERIC_LIBC_MTAG_H 1
+
+/* Generic bindings for systems that do not support memory tagging.  */
+
+/* Used to ensure additional alignment when objects need to have distinct
+   tags.  */
+#define __MTAG_GRANULE_SIZE 1
+
+/* Non-zero if memory obtained via morecore (sbrk) is not tagged.  */
+#define __MTAG_SBRK_UNTAGGED 0
+
+/* Extra flags to pass to mmap() to request a tagged region of memory.  */
+#define __MTAG_MMAP_FLAGS 0
+
+/* Set the tags for a region of memory, which must have size and alignment
+   that are multiples of __MTAG_GRANULE_SIZE.  Size cannot be zero.
+   void *__libc_mtag_tag_region (const void *, size_t)  */
+#define __libc_mtag_tag_region(p, s) (p)
+
+/* Optimized equivalent to __libc_mtag_tag_region followed by memset.  */
+#define __libc_mtag_memset_with_tag memset
+
+/* Convert address P to a pointer that is tagged correctly for that
+   location.
+   void *__libc_mtag_address_get_tag (void*)  */
+#define __libc_mtag_address_get_tag(p) (p)
+
+/* Assign a new (random) tag to a pointer P (does not adjust the tag on
+   the memory addressed).
+   void *__libc_mtag_new_tag (void*)  */
+#define __libc_mtag_new_tag(p) (p)
+
+#endif /* _GENERIC_LIBC_MTAG_H */