[glibc/arm/morello/main] cheri: malloc: Disable pointer protection

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5440678ee1801698f97c52e227aaeff7a84e4516

commit 5440678ee1801698f97c52e227aaeff7a84e4516
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Wed Jul 7 14:21:40 2021 +0100

    cheri: malloc: Disable pointer protection
    
    Such arithmetic invalidates capabilities so this security measure does
    not work for CHERI.
    
    Note: the architecture makes it hard to corrupt pointers in malloc
    metadata, but not impossible: current allocation bounds include the
    metadata and capabilities are not revoked after free. These issues can
    be fixed by a capability aware malloc.

Diff:
---
 malloc/malloc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index bd3c76ed31..062ca0dc0a 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -341,8 +341,12 @@ Fatal glibc error: malloc assertion failure in %s: %s\n",
    It assumes a minimum page size of 4096 bytes (12 bits).  Systems with
    larger pages provide less entropy, although the pointer mangling
    still works.  */
+#ifdef __CHERI_PURE_CAPABILITY__
+#define PROTECT_PTR(pos, ptr) (ptr)
+#else
 #define PROTECT_PTR(pos, ptr) \
   ((__typeof (ptr)) ((((size_t) pos) >> 12) ^ ((size_t) ptr)))
+#endif
 #define REVEAL_PTR(ptr)  PROTECT_PTR (&ptr, ptr)
 
 /*