Enabling ARM64 Memory Tagging Extension to Catch Memory Safety Bugs in C/C++

Desired Outcome

Run a C/C++ program under ARM64 Memory Tagging Extension (MTE) so that spatial or temporal memory errors trigger a synchronous tag‑check fault, allowing you to detect bugs with low runtime overhead.

Prerequisites

1. Hardware: an ARMv8.5‑A or later core that implements MTE (check for the MTE feature flag).
2. Kernel: a build with CONFIG_ARM64_MTE=y (or a compatible distribution kernel that enables it).
3. Toolchain: LLVM/Clang version that supports -fsanitize=memtag (e.g., clang 15+).
4. Root or sudo access to load kernel parameters and view kernel logs.

Focused Procedure

1. Verify CPU support

   # Run as any user
   lscpu | grep -i mte
   # Expected output includes a line like: Flags: ... mte ...
   

   If no mte flag appears, the processor cannot use MTE.

2. Ensure the kernel has MTE enabled

   Check the running kernel configuration:

   zgrep CONFIG_ARM64_MTE /proc/config.gz
   # or, if config is not available:
   cat /boot/config-$(uname -r) | grep CONFIG_ARM64_MTE
   

   The value should be y. If it is n or missing, you need a kernel built with MTE support or a boot parameter that activates it.

3. Activate MTE at boot (if not already active)

   Add the kernel command‑line option memtag=on (e.g., via GRUB) and reboot. After reboot, confirm:

   cat /sys/kernel/debug/arm64/mte/enable
   # Should print 1
   

4. Create a test program with a known bug

   # test.c
   #include 
   #include 
   int main(void) {
       char buf[8];
       strcpy(buf, "this is too long"); // intentional overflow
       printf("%s\n", buf);
       return 0;
   }
   

5. Compile with MTE sanitizer

   # Run in a normal user directory
   clang -fsanitize=memtag -g -O1 test.c -o test-mte
   

   The -fsanitize=memtag flag instructs the compiler to emit IRG (Insert Random Tag) instructions for allocations and to preserve the tag in the top byte of pointers.

6. Run the binary and observe the fault

   ./test-mte
   # The program should abort with a SIGSEGV (or SIGILL) and print a message like:
   # tag check failure
   

   If the program terminates without a tag‑check message, MTE may not be active for the process.

7. Check kernel logs for the tag‑check fault

   dmesg | grep -i tag
   # or
   journalctl -k | grep -i tag
   

   Look for lines containing "MTE tag check fault" or similar, which include the faulting address and the process name.

Expected Checks

• CPU reports the mte feature.
• Kernel shows CONFIG_ARM64_MTE=y (or memtag=on active).
• The compiled binary runs and aborts with a tag‑check fault when the overflow occurs.
• Kernel log contains a tag‑check fault entry matching the faulting instruction.

Recovery Options

• If MTE causes unwanted crashes due to legitimate pointer arithmetic that modifies the top byte, rebuild the application without -fsanitize=memtag.
• To temporarily disable MTE for all processes, reboot with the kernel parameter memtag=off or set /sys/kernel/debug/arm64/mte/enable to 0 (requires root).
• For production use, consider enabling MTE only in testing or staging environments; the performance impact is low (~2‑5 %) compared with AddressSanitizer.