linux-kernel - [PATCH 4/6] kexec_file: Adjust declaration of kexec

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Date:   Mon,  5 Jun 2017 21:52:33 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Daniel Micay <danielmicay@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 4/6] kexec_file: Adjust declaration of kexec_purgatory

Defining kexec_purgatory as a zero-length char array upsets compile
time size checking. Since this is built on a per-arch basis, define
it as an unsized char array (like is done for other similar things,
e.g. linker sections). This silences the warning generated by the future
CONFIG_FORTIFY_SOURCE, which did not like the memcmp() of a "0 byte"
array. This drops the __weak and uses an extern instead, since both
users define kexec_purgatory.

Cc: Daniel Micay <danielmicay@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/kexec_file.c     | 7 -------
 kernel/kexec_internal.h | 2 ++
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index f78f719dae36..5710591a9b6d 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -26,13 +26,6 @@
 #include <linux/vmalloc.h>
 #include "kexec_internal.h"
 
-/*
- * Declare these symbols weak so that if architecture provides a purgatory,
- * these will be overridden.
- */
-char __weak kexec_purgatory[0];
-size_t __weak kexec_purgatory_size = 0;
-
 static int kexec_calculate_store_digests(struct kimage *image);
 
 /* Architectures can provide this probe function */
diff --git a/kernel/kexec_internal.h b/kernel/kexec_internal.h
index 799a8a452187..50dfcb039a41 100644
--- a/kernel/kexec_internal.h
+++ b/kernel/kexec_internal.h
@@ -17,6 +17,8 @@ extern struct mutex kexec_mutex;
 #ifdef CONFIG_KEXEC_FILE
 #include <linux/purgatory.h>
 void kimage_file_post_load_cleanup(struct kimage *image);
+extern char kexec_purgatory[];
+extern size_t kexec_purgatory_size;
 #else /* CONFIG_KEXEC_FILE */
 static inline void kimage_file_post_load_cleanup(struct kimage *image) { }
 #endif /* CONFIG_KEXEC_FILE */
-- 
2.7.4