[glibc/arm/morello/main] cheri: malloc: Ensure the mappings have RW permission

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=af11ceae3867a3786308738a6870a8f1016a865e

commit af11ceae3867a3786308738a6870a8f1016a865e
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Fri Oct 21 12:35:33 2022 +0100

    cheri: malloc: Ensure the mappings have RW permission
    
    The arena allocator incrementally applies RW mprotect to a PROT_NONE
    mapping.  Use PROT_MAX to ensure the pointers derived from the original
    mapping have RW capability permission.

Diff:
---
 malloc/malloc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 02df29d2ad..701adbebca 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -1134,8 +1134,16 @@ static mchunkptr mremap_chunk(mchunkptr p, size_t new_size);
 # define MAP_NORESERVE 0
 #endif
 
+/* Allow RW mprotect later, on CHERI this means RW capability permission.  */
+#ifdef PROT_MAX
+# define PROT_MAX_RW PROT_MAX (PROT_READ | PROT_WRITE)
+#else
+# define PROT_MAX_RW 0
+#endif
+
 #define MMAP(addr, size, prot, flags) \
- __mmap((addr), (size), (prot), (flags)|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0)
+ __mmap((addr), (size), (prot)|PROT_MAX_RW, \
+	(flags)|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0)
 
 
 /*