rt: Add a canary value to the end of every stack

Check it on upcall entry and exit, and on stack deletion

src/rt/rust_task.cpp

@@ -49,6 +49,12 @@
 #endif
 #endif
 
+// A value that goes at the end of the stack and must not be touched
+const uint8_t stack_canary[] = {0xAB, 0xCD, 0xAB, 0xCD,
+                                0xAB, 0xCD, 0xAB, 0xCD,
+                                0xAB, 0xCD, 0xAB, 0xCD,
+                                0xAB, 0xCD, 0xAB, 0xCD};
+
 // Stack size
 size_t g_custom_min_stack_size = 0;
 
@@ -95,7 +101,8 @@ config_valgrind_stack(stk_seg *stk) {
     // old stack segments, since the act of popping the stack previously
     // caused valgrind to consider the whole thing inaccessible.
     size_t sz = stk->end - (uintptr_t)&stk->data[0];
-    VALGRIND_MAKE_MEM_UNDEFINED(stk->data, sz);
+    VALGRIND_MAKE_MEM_UNDEFINED(stk->data + sizeof(stack_canary),
+                                sz - sizeof(stack_canary));
 #endif
 }
 
@@ -110,6 +117,18 @@ free_stk(rust_task *task, stk_seg *stk) {
     task->free(stk);
 }
 
+static void
+add_stack_canary(stk_seg *stk) {
+    memcpy(stk->data, stack_canary, sizeof(stack_canary));
+    assert(sizeof(stack_canary) == 16 && "Stack canary was not the expected size");
+}
+
+static void
+check_stack_canary(stk_seg *stk) {
+    assert(!memcmp(stk->data, stack_canary, sizeof(stack_canary))
+      && "Somebody killed the canary");
+}
+
 static stk_seg*
 new_stk(rust_scheduler *sched, rust_task *task, size_t requested_sz)
 {
@@ -151,6 +170,7 @@ new_stk(rust_scheduler *sched, rust_task *task, size_t requested_sz)
     stk_seg *stk = (stk_seg *)task->malloc(sz, "stack");
     LOGPTR(task->sched, "new stk", (uintptr_t)stk);
     memset(stk, 0, sizeof(stk_seg));
+    add_stack_canary(stk);
     stk->prev = NULL;
     stk->next = task->stk;
     stk->end = (uintptr_t) &stk->data[rust_stk_sz + RED_ZONE_SIZE];
@@ -165,6 +185,7 @@ static void
 del_stk(rust_task *task, stk_seg *stk)
 {
     assert(stk == task->stk && "Freeing stack segments out of order!");
+    check_stack_canary(stk);
 
     task->stk = stk->next;
 
@@ -784,6 +805,11 @@ rust_task::on_rust_stack() {
     return sp_in_stk_seg(get_sp(), stk);
 }
 
+void
+rust_task::check_stack_canary() {
+    ::check_stack_canary(stk);
+}
+
 //
 // Local Variables:
 // mode: C++

src/rt/rust_task.h

@@ -203,6 +203,7 @@ rust_task : public kernel_owned<rust_task>, rust_cond
     void record_stack_limit();
     void reset_stack_limit();
     bool on_rust_stack();
+    void check_stack_canary();
 };
 
 //

src/rt/rust_upcall.cpp

@@ -27,14 +27,21 @@ check_stack_alignment() __attribute__ ((aligned (16)));
 static void check_stack_alignment() { }
 #endif
 
+static inline void
+do_sanity_check(rust_task *task) {
+    check_stack_alignment();
+    task->check_stack_canary();
+}
+
 #define UPCALL_SWITCH_STACK(A, F) call_upcall_on_c_stack((void*)A, (void*)F)
 
 inline void
 call_upcall_on_c_stack(void *args, void *fn_ptr) {
-    check_stack_alignment();
     rust_task *task = rust_scheduler::get_task();
+    do_sanity_check(task);
     rust_scheduler *sched = task->sched;
     sched->c_context.call_shim_on_c_stack(args, fn_ptr);
+    do_sanity_check(task);
 }
 
 extern "C" void record_sp(void *limit);
@@ -48,8 +55,8 @@ extern "C" void record_sp(void *limit);
  */
 extern "C" CDECL void
 upcall_call_shim_on_c_stack(void *args, void *fn_ptr) {
-    check_stack_alignment();
     rust_task *task = rust_scheduler::get_task();
+    do_sanity_check(task);
 
     // FIXME (1226) - The shim functions generated by rustc contain the
     // morestack prologue, so we need to let them know they have enough
@@ -65,6 +72,7 @@ upcall_call_shim_on_c_stack(void *args, void *fn_ptr) {
 
     task = rust_scheduler::get_task();
     task->record_stack_limit();
+    do_sanity_check(task);
 }
 
 /**********************************************************************/
@@ -634,9 +642,10 @@ upcall_del_stack() {
 // needs to acquire the value of the stack pointer
 extern "C" CDECL void
 upcall_reset_stack_limit() {
-    check_stack_alignment();
     rust_task *task = rust_scheduler::get_task();
+    do_sanity_check(task);
     task->reset_stack_limit();
+    do_sanity_check(task);
 }
 
 //