boot: Simplify object erasure

This erase_obj() machinery looks like voodoo and creates an awful lot of
noise as soon as we get back to building with -O0. We can do this in a
more simple way by introducing a struct that holds the information we
need on cleanup. When building with optimization enabled, all this gets
inlined and the eraser vanishes.

2 files changed, 43 insertions, 0 deletions

diff --git a/src/fundamental/memory-util-fundamental.h b/src/fundamental/memory-util-fundamental.h
new file mode 100644
index 0000000000..9015300ae8
--- /dev/null
+++ b/src/fundamental/memory-util-fundamental.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <stddef.h>
+
+#ifdef SD_BOOT
+#  include "efi-string.h"
+#else
+#  include <string.h>
+#endif
+
+#include "macro-fundamental.h"
+
+#if defined(HAVE_EXPLICIT_BZERO)
+static inline void *explicit_bzero_safe(void *p, size_t l) {
+        if (p && l > 0)
+                explicit_bzero(p, l);
+
+        return p;
+}
+#else
+static inline void *explicit_bzero_safe(void *p, size_t l) {
+        if (p && l > 0) {
+                memset(p, 0, l);
+                __asm__ __volatile__("" : : "r"(p) : "memory");
+        }
+        return p;
+}
+#endif
+
+struct VarEraser {
+        void *p;
+        size_t size;
+};
+
+static inline void erase_var(struct VarEraser *e) {
+        explicit_bzero_safe(e->p, e->size);
+}
+
+/* Mark var to be erased when leaving scope. */
+#define CLEANUP_ERASE(var) \
+        _cleanup_(erase_var) _unused_ struct VarEraser CONCATENATE(_eraser_, UNIQ) = { .p = &var, .size = sizeof(var) }
diff --git a/src/fundamental/meson.build b/src/fundamental/meson.build
index 3810d6b456..4b8e32337d 100644
--- a/src/fundamental/meson.build
+++ b/src/fundamental/meson.build
@@ -6,6 +6,7 @@ fundamental_headers = files(
         'bootspec-fundamental.h',
         'efivars-fundamental.h',
         'macro-fundamental.h',
+        'memory-util-fundamental.h',
         'sha256.h',
         'string-util-fundamental.h',
         'tpm-pcr.h',