(Xcode 26.2, iPhone 17 Pro)
I can't seem to get hardware tag checks to work in an app launched without the special "Hardware Memory Tagging" diagnostics. In other words, I have been unable to reproduce the crash example at 6:40 in Apple's video "Secure your app with Memory Integrity Enforcement".
When I write a heap overflow or a UAF, it is picked up perfectly provided I enable the "Hardware Memory Tagging" feature under Scheme Diagnostics.
If I instead add the Enhanced Security capability with the memory-tagging related entitlements:
I'm seeing distinct memory tags being assigned in pointers returned by malloc (without the capability, this is not the case)
Tag mismatches are not being caught or enforced, regardless of soft mode
The behaviour is the same whether I launch from Xcode without "Hardware Memory Tagging", or if I launch the app by tapping it on launchpad. In case it was related to debug builds, I also tried creating an ad hoc IPA and it didn't make any difference.
I realise there's a wrinkle here that the debugger sets MallocTagAll=1, so possibly it will pick up a wider range of issues. However I would have expected that a straight UAF would be caught. For example, this test code demonstrates that tagging is active but it doesn't crash:
#define PTR_TAG(p) ((unsigned)(((uintptr_t)(p) >> 56) & 0xF))
void *p1 = malloc(32);
void *p2 = malloc(32);
void *p3 = malloc(32);
os_log(OS_LOG_DEFAULT, "p1 = %p (tag: %u)\n", p1, PTR_TAG(p1));
os_log(OS_LOG_DEFAULT, "p2 = %p (tag: %u)\n", p2, PTR_TAG(p2));
os_log(OS_LOG_DEFAULT, "p3 = %p (tag: %u)\n", p3, PTR_TAG(p3));
free(p2);
void *p2_realloc = malloc(32);
os_log(OS_LOG_DEFAULT, "p2 after free+malloc = %p (tag: %u)\n", p2_realloc, PTR_TAG(p2_realloc));
// Is p2_realloc the same address as p2 but different tag?
os_log(OS_LOG_DEFAULT, "Same address? %s\n",
((uintptr_t)p2 & 0x00FFFFFFFFFFFFFF) == ((uintptr_t)p2_realloc & 0x00FFFFFFFFFFFFFF)
? "YES" : "NO");
// Now try to use the OLD pointer p2
os_log(OS_LOG_DEFAULT, "Attempting use-after-free via old pointer p2...\n");
volatile char c = *(volatile char *)p2; // Should this crash?
os_log(OS_LOG_DEFAULT, "Read succeeded! Value: %d\n", c);
Example output:
p1 = 0xf00000b71019660 (tag: 15)
p2 = 0x200000b711958c0 (tag: 2)
p3 = 0x300000b711958e0 (tag: 3)
p2 after free+malloc = 0x700000b71019680 (tag: 7)
Same address? NO
Attempting use-after-free via old pointer p2...
Read succeeded! Value: -55
For reference, these are my entitlements.
[Dict]
[Key] application-identifier
[Value]
[String] …
[Key] com.apple.developer.team-identifier
[Value]
[String] …
[Key] com.apple.security.hardened-process
[Value]
[Bool] true
[Key] com.apple.security.hardened-process.checked-allocations
[Value]
[Bool] true
[Key] com.apple.security.hardened-process.checked-allocations.enable-pure-data
[Value]
[Bool] true
[Key] com.apple.security.hardened-process.dyld-ro
[Value]
[Bool] true
[Key] com.apple.security.hardened-process.enhanced-security-version
[Value]
[Int] 1
[Key] com.apple.security.hardened-process.hardened-heap
[Value]
[Bool] true
[Key] com.apple.security.hardened-process.platform-restrictions
[Value]
[Int] 2
[Key] get-task-allow
[Value]
[Bool] true
What do I need to do to make Memory Integrity Enforcement do something outside the debugger?
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