[sanitizer-common] Improve mach_vm_region_recurse error handling

Some sanitizers use mach_vm_region_recurse on macOS to find a sufficiently
large gap to allocate shadow memory. Some sandboxes do not allow this.

When we get KERN_DENIED, we suggest to the user that it may have been
blocked by the sandbox.

For error codes other than KERN_INVALID_ADDRESS and KERN_DENIED,
we make sure to log a message and not use the address.

rdar://145860383

Author: ndrewh

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

@@ -1265,17 +1265,34 @@ uptr FindAvailableMemoryRange(uptr size, uptr alignment, uptr left_padding,
     kr = mach_vm_region_recurse(mach_task_self(), &address, &vmsize, &depth,
                                 (vm_region_info_t)&vminfo, &count);
 
-    // There are cases where going beyond the processes' max vm does
-    // not return KERN_INVALID_ADDRESS so we check for going beyond that
-    // max address as well.
-    if (kr == KERN_INVALID_ADDRESS || address > max_vm_address) {
+    if (kr == KERN_SUCCESS) {
+      // There are cases where going beyond the processes' max vm does
+      // not return KERN_INVALID_ADDRESS so we check for going beyond that
+      // max address as well.
+      if (address > max_vm_address) {
+        address = max_vm_address;
+        kr = -1;  // break after this iteration.
+      }
+
+      if (max_occupied_addr)
+        *max_occupied_addr = address + vmsize;
+    } else if (kr == KERN_INVALID_ADDRESS) {
       // No more regions beyond "address", consider the gap at the end of VM.
       address = max_vm_address;
-      vmsize = 0;
-      kr = -1;  // break after this iteration.
+
+      // We will break after this iteration anyway since kr != KERN_SUCCESS
+    } else if (kr == KERN_DENIED) {
+      Report("ERROR: Unable to find a memory range for dynamic shadow.\n");
+      Report("HINT: Ensure mach_vm_region_recurse is allowed under sandbox.\n");
+      Die();
     } else {
-      if (max_occupied_addr) *max_occupied_addr = address + vmsize;
+      Report("WARNING: mach_vm_region_recurse returned unexpected code %d\n",
+             kr);
+      DCHECK(false && "mach_vm_region_recurse returned unexpected code");
+      break;  // address is not valid unless KERN_SUCCESS, therefore we must not
+              // use it.
     }
+
     if (free_begin != address) {
       // We found a free region [free_begin..address-1].
       uptr gap_start = RoundUpTo((uptr)free_begin + left_padding, alignment);

compiler-rt/test/asan/TestCases/Darwin/sandbox-vm-region-recurse.cpp

@@ -0,0 +1,34 @@
+// Check that if mach_vm_region_recurse is disallowed by sandbox, we report a message saying so.
+
+// RUN: %clangxx_asan -O0 %s -o %t
+// RUN: not %run sandbox-exec -p '(version 1)(allow default)(deny syscall-mig (kernel-mig-routine mach_vm_region_recurse))' %t 2>&1 | FileCheck --check-prefix=CHECK-DENY %s
+// RUN: not %run %t 2>&1 | FileCheck --check-prefix=CHECK-ALLOW %s
+// RUN: %clangxx_asan -O3 %s -o %t
+// RUN: not %run sandbox-exec -p '(version 1)(allow default)(deny syscall-mig (kernel-mig-routine mach_vm_region_recurse))' %t 2>&1 | FileCheck --check-prefix=CHECK-DENY %s
+// RUN: not %run %t 2>&1 | FileCheck --check-prefix=CHECK-ALLOW %s
+
+// sandbox-exec isn't available on iOS
+// UNSUPPORTED: ios
+
+// x86_64 does not use ASAN_SHADOW_OFFSET_DYNAMIC
+// UNSUPPORTED: x86_64-darwin
+// UNSUPPORTED: x86_64h-darwin
+
+#include <stdlib.h>
+
+int main() {
+  char *x = (char *)malloc(10 * sizeof(char));
+  free(x);
+  return x[5];
+  // CHECK-ALLOW: {{.*ERROR: AddressSanitizer: heap-use-after-free on address}}
+  // CHECK-DENY-NOT: {{.*ERROR: AddressSanitizer: heap-use-after-free on address}}
+  // CHECK-ALLOW: {{READ of size 1 at 0x.* thread T0}}
+  // CHECK-ALLOW: {{    #0 0x.* in main}}
+  // CHECK-ALLOW: {{freed by thread T0 here:}}
+  // CHECK-ALLOW: {{    #0 0x.* in free}}
+  // CHECK-ALLOW: {{    #1 0x.* in main}}
+  // CHECK-ALLOW: {{previously allocated by thread T0 here:}}
+  // CHECK-ALLOW: {{    #0 0x.* in malloc}}
+  // CHECK-ALLOW: {{    #1 0x.* in main}}
+  // CHECK-DENY: {{.*HINT: Ensure mach_vm_region_recurse is allowed under sandbox}}
+}