From d2320a69dfc88e713ab357267be8dfad8275e53b Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <pcc@google.com>
Date: Thu, 1 Dec 2022 14:35:20 -0800
Subject: [PATCH] On aarch64, use PROT_MTE on arena mapping if MTE is enabled.

This automatically uses MTE-enabled mappings (consistent with the rest
of the system) if MTE is enabled via a libc-specific environment variable:

glibc:  GLIBC_TUNABLES=glibc.mem.tagging=1
bionic: MEMTAG_OPTIONS=async
---
 arena.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arena.c b/arena.c
index f1933ed..e8fc3a4 100644
--- a/arena.c
+++ b/arena.c
@@ -19,6 +19,7 @@
 #include <string.h>
 #include <sys/ipc.h>
 #include <sys/mman.h>
+#include <sys/prctl.h>
 #include <sys/shm.h>
 #include <sys/syscall.h>
 #include <unistd.h>
@@ -232,15 +233,22 @@ static void check_thp_state(void) {
 void *alloc_arena_mmap(size_t page_size, bool use_thp, size_t arena_size, int fd) {
   void *arena;
   size_t pagemask = page_size - 1;
+  int prot = PROT_READ | PROT_WRITE;
   int flags;
 
+#ifdef __aarch64__
+  int tac = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
+  if (tac != -1 && (tac & PR_MTE_TCF_MASK))
+    prot |= PROT_MTE;
+#endif
+
   if (fd == -1)
     flags = MAP_PRIVATE | MAP_ANONYMOUS | get_page_size_flags(page_size);
   else
     flags = MAP_SHARED;
 
   arena_size = (arena_size + pagemask) & ~pagemask;
-  arena = mmap(0, arena_size, PROT_READ | PROT_WRITE, flags, fd, 0);
+  arena = mmap(0, arena_size, prot, flags, fd, 0);
   if (arena == MAP_FAILED) {
     perror("mmap");
     exit(1);