From ffff09335760efc655faf093b6fbb364cfae4ad7 Mon Sep 17 00:00:00 2001
From: Jan Janssen <medhefgo@web.de>
Date: Sat, 7 Jan 2023 22:16:52 +0100
Subject: [PATCH] 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.

(cherry picked from commit 3f92dc2fd4070b213e6bc85263a9bef06ec9a486)

Related: RHEL-16182
---
 src/basic/memory-util.c                   | 18 ----------
 src/basic/memory-util.h                   | 12 +------
 src/boot/efi/random-seed.c                |  1 +
 src/fundamental/memory-util-fundamental.h | 42 +++++++++++++++++++++++
 src/fundamental/meson.build               |  1 +
 5 files changed, 45 insertions(+), 29 deletions(-)
 create mode 100644 src/fundamental/memory-util-fundamental.h

diff --git a/src/basic/memory-util.c b/src/basic/memory-util.c
index 2983762117..c4f54c7b4e 100644
--- a/src/basic/memory-util.c
+++ b/src/basic/memory-util.c
@@ -38,21 +38,3 @@ bool memeqbyte(uint8_t byte, const void *data, size_t length) {
         /* Now we know first 16 bytes match, memcmp() with self.  */
         return memcmp(data, p + 16, length) == 0;
 }
-
-#if !HAVE_EXPLICIT_BZERO
-/*
- * The pointer to memset() is volatile so that compiler must de-reference the pointer and can't assume that
- * it points to any function in particular (such as memset(), which it then might further "optimize"). This
- * approach is inspired by openssl's crypto/mem_clr.c.
- */
-typedef void *(*memset_t)(void *,int,size_t);
-
-static volatile memset_t memset_func = memset;
-
-void* explicit_bzero_safe(void *p, size_t l) {
-        if (l > 0)
-                memset_func(p, '\0', l);
-
-        return p;
-}
-#endif
diff --git a/src/basic/memory-util.h b/src/basic/memory-util.h
index eea9c0e92f..d26a0918e1 100644
--- a/src/basic/memory-util.h
+++ b/src/basic/memory-util.h
@@ -9,6 +9,7 @@
 
 #include "alloc-util.h"
 #include "macro.h"
+#include "memory-util-fundamental.h"
 
 size_t page_size(void) _pure_;
 #define PAGE_ALIGN(l) ALIGN_TO((l), page_size())
@@ -91,17 +92,6 @@ static inline void *mempmem_safe(const void *haystack, size_t haystacklen, const
         return (uint8_t*) p + needlelen;
 }
 
-#if HAVE_EXPLICIT_BZERO
-static inline void* explicit_bzero_safe(void *p, size_t l) {
-        if (l > 0)
-                explicit_bzero(p, l);
-
-        return p;
-}
-#else
-void *explicit_bzero_safe(void *p, size_t l);
-#endif
-
 static inline void* erase_and_free(void *p) {
         size_t l;
 
diff --git a/src/boot/efi/random-seed.c b/src/boot/efi/random-seed.c
index aea4f7e532..3c9df5bb54 100644
--- a/src/boot/efi/random-seed.c
+++ b/src/boot/efi/random-seed.c
@@ -3,6 +3,7 @@
 #include <efi.h>
 #include <efilib.h>
 
+#include "memory-util-fundamental.h"
 #include "missing_efi.h"
 #include "random-seed.h"
 #include "secure-boot.h"
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',