use erts_mem_guard for global literals

erlang · Jul 11, 2024 · 9d0aba7 · 9d0aba7
1 parent 6f11039
commit 9d0aba7
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Showing 3 changed files with 64 additions and 17 deletions.
diff --git a/erts/emulator/beam/erl_global_literals.c b/erts/emulator/beam/erl_global_literals.c
@@ -25,14 +25,12 @@
 #include "sys.h"
 #include "global.h"
 #include "erl_global_literals.h"
+#include "erl_mmap.h"
+
+
+#define GLOBAL_LITERAL_INITIAL_SIZE (1<<16)
+#define GLOBAL_LITERAL_EXPAND_SIZE 512
 
-#ifndef DEBUG
-#  define GLOBAL_LITERAL_INITIAL_SIZE (1<<16)
-#  define GLOBAL_LITERAL_EXPAND_SIZE 512
-#else
-#  define GLOBAL_LITERAL_INITIAL_SIZE 0
-#  define GLOBAL_LITERAL_EXPAND_SIZE 0
-#endif
 
 /*
  * Global Constant Literals
@@ -89,11 +87,22 @@ ErtsLiteralArea *erts_global_literal_iterate_area(ErtsLiteralArea *prev)
 
 static void expand_shared_global_literal_area(Uint heap_size)
 {
+    const size_t size = sizeof(struct global_literal_chunk) +
+                        (heap_size - 1) * sizeof(Eterm);
     struct global_literal_chunk *chunk;
+
+#ifndef DEBUG 
+    chunk = (struct global_literal_chunk *) erts_alloc(ERTS_ALC_T_LITERAL, size); 
+#else
+    /* erts_mem_guard requires the memory area to be page aligned. Overallocate
+     * and align the address to ensure that is the case. */
+    UWord address;
+    address = (UWord) erts_alloc(ERTS_ALC_T_LITERAL, size + sys_page_size * 2);
+    heap_size += address & (sys_page_size - 1);
+    address = (address + (sys_page_size - 1)) & ~(sys_page_size - 1);
+    chunk = (struct global_literal_chunk *) address;
+#endif
 
-    chunk = erts_alloc(ERTS_ALC_T_LITERAL,
-                       sizeof(struct global_literal_chunk) +
-                        (heap_size - 1) * sizeof(Eterm));
     chunk->hp = &chunk->area.start[0];
     chunk->area.end = &chunk->hp[heap_size];
     chunk->area.off_heap = NULL;
@@ -117,11 +126,33 @@ Eterm *erts_global_literal_allocate(Uint heap_size, struct erl_off_heap_header *
     *ohp = &global_literal_chunk->area.off_heap;
     hp = global_literal_chunk->hp;
     global_literal_chunk->hp += heap_size;
+
+#ifdef DEBUG
+    {
+        struct global_literal_chunk *chunk = global_literal_chunk;
+        erts_mem_guard(&chunk->area.start[0], 
+                       (chunk->area.end - &chunk->area.start[0]) * sizeof(Eterm), 
+                       1, 
+                       1);
+    }
+#endif
+
     return hp;
 }
 
 void erts_global_literal_register(Eterm *variable, Eterm *hp, Uint heap_size) {
     erts_set_literal_tag(variable, hp, heap_size);
+
+#ifdef DEBUG
+    {
+        struct global_literal_chunk *chunk = global_literal_chunk;
+        erts_mem_guard(&chunk->area.start[0], 
+                       (chunk->area.end - &chunk->area.start[0]) * sizeof(Eterm), 
+                       1, 
+                       0);
+    }
+#endif
+
     erts_mtx_unlock(&global_literal_lock);
 }
 

diff --git a/erts/emulator/sys/common/erl_mmap.c b/erts/emulator/sys/common/erl_mmap.c
@@ -32,19 +32,35 @@
 #include <sys/mman.h>
 #endif
 
-int erts_mem_guard(void *p, UWord size) {
+int erts_mem_guard(void *p, UWord size, int readable, int writable) {
+
 #if defined(WIN32)
     DWORD oldProtect;
+    DWORD newProtect = PAGE_NOACCESS;
     BOOL success;
-
+    if (readable && writable) {
+        newProtect = PAGE_READWRITE;
+    } else if (readable) {
+        newProtect = PAGE_READONLY;
+    } else {
+        ERTS_INTERNAL_ERROR(!"mem_guard invalid page permissions");
+    }
     success = VirtualProtect((LPVOID*)p,
                              size,
-                             PAGE_NOACCESS,
+                             newProtect,
                              &oldProtect);
 
     return success ? 0 : -1;
 #elif defined(HAVE_SYS_MMAN_H)
-    return mprotect(p, size, PROT_NONE);
+    int flags = 0;
+
+    if (writable) {
+        flags |= PROT_WRITE;
+    }
+    if (readable) {
+        flags |= PROT_READ;
+    }
+    return mprotect(p, size, flags);
 #else
     errno = ENOTSUP;
     return -1;

diff --git a/erts/emulator/sys/common/erl_mmap.h b/erts/emulator/sys/common/erl_mmap.h
@@ -182,10 +182,10 @@ void hard_dbg_remove_mseg(void* seg, UWord sz);
 
 #endif /* HAVE_ERTS_MMAP */
 
-/* Marks the given memory region as permanently inaccessible.
- *
+/* Changes the permissions of the given memory region. 
+ * Assumes proper page alignment.
  * Returns 0 on success, and -1 on error. */
-int erts_mem_guard(void *p, UWord size);
+int erts_mem_guard(void *p, UWord size, int readable, int writable);
 
 /* Marks the given memory region as unused without freeing it, letting the OS
  * reclaim its physical memory with the promise that we'll get it back (without