ntdll: Treat read faults on readable pages as write faults on macOS.

Working around a Rosetta bug on Apple Silicon - faults for certain instructions (e.g. lock cmpxchg8b) are misreported, which can break VPROT_WRITEWATCH handling.

ntdll: Treat read faults on readable pages as write faults on macOS.
1b310a5a · Tim Clem · Alexandre Julliard · 9d255d6d · 1b310a5a
Commit 1b310a5a authored Feb 04, 2022 by Tim Clem Committed by Alexandre Julliard Jun 22, 2023
Hide whitespace changes
Inline Side-by-side

Showing with 10 additions and 0 deletions

virtual.c dlls/ntdll/unix/virtual.c +10 -0

No files found.
--- a/dlls/ntdll/unix/virtual.c
+++ b/dlls/ntdll/unix/virtual.c
@@ -3692,6 +3692,16 @@ NTSTATUS virtual_handle_fault( void *addr, DWORD err, void *stack )

    mutex_lock( &virtual_mutex );  /* no need for signal masking inside signal handler */
    vprot = get_page_vprot( page );
+
+#ifdef __APPLE__
+    /* Rosetta on Apple Silicon misreports certain write faults as read faults. */
+    if (err == EXCEPTION_READ_FAULT && (get_unix_prot( vprot ) & PROT_READ))
+    {
+        WARN( "treating read fault in a readable page as a write fault, addr %p\n", addr );
+        err = EXCEPTION_WRITE_FAULT;
+    }
+#endif
+
    if (!is_inside_signal_stack( stack ) && (vprot & VPROT_GUARD))
    {
        struct thread_stack_info stack_info;