[patch 19/27] kernel/kexec_file.c: make purgatory_info->ehdr const

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From: Philipp Rudo <prudo@xxxxxxxxxxxxxxxxxx>
Subject: kernel/kexec_file.c: make purgatory_info->ehdr const

The kexec_purgatory buffer is read-only.  Thus all pointers into
kexec_purgatory are read-only, too.  Point this out by explicitly marking
purgatory_info->ehdr as 'const' and update the comments in purgatory_info.

Link: http://lkml.kernel.org/r/20180321112751.22196-4-prudo@xxxxxxxxxxxxxxxxxx
Signed-off-by: Philipp Rudo <prudo@xxxxxxxxxxxxxxxxxx>
Acked-by: Dave Young <dyoung@xxxxxxxxxx>
Cc: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 include/linux/kexec.h |   17 +++++++++++------
 kernel/kexec_file.c   |    4 ++--
 2 files changed, 13 insertions(+), 8 deletions(-)

diff -puN include/linux/kexec.h~kexec_file-make-purgatory_info-ehdr-const include/linux/kexec.h
--- a/include/linux/kexec.h~kexec_file-make-purgatory_info-ehdr-const
+++ a/include/linux/kexec.h
@@ -99,14 +99,19 @@ struct compat_kexec_segment {
 
 #ifdef CONFIG_KEXEC_FILE
 struct purgatory_info {
-	/* Pointer to elf header of read only purgatory */
-	Elf_Ehdr *ehdr;
-
-	/* Pointer to purgatory sechdrs which are modifiable */
+	/*
+	 * Pointer to elf header at the beginning of kexec_purgatory.
+	 * Note: kexec_purgatory is read only
+	 */
+	const Elf_Ehdr *ehdr;
+	/*
+	 * Temporary, modifiable buffer for sechdrs used for relocation.
+	 * This memory can be freed post image load.
+	 */
 	Elf_Shdr *sechdrs;
 	/*
-	 * Temporary buffer location where purgatory is loaded and relocated
-	 * This memory can be freed post image load
+	 * Temporary, modifiable buffer for stripped purgatory used for
+	 * relocation. This memory can be freed post image load.
 	 */
 	void *purgatory_buf;
 
diff -puN kernel/kexec_file.c~kexec_file-make-purgatory_info-ehdr-const kernel/kexec_file.c
--- a/kernel/kexec_file.c~kexec_file-make-purgatory_info-ehdr-const
+++ a/kernel/kexec_file.c
@@ -941,7 +941,7 @@ int kexec_load_purgatory(struct kimage *
 	if (kexec_purgatory_size <= 0)
 		return -EINVAL;
 
-	pi->ehdr = (Elf_Ehdr *)kexec_purgatory;
+	pi->ehdr = (const Elf_Ehdr *)kexec_purgatory;
 
 	ret = __kexec_load_purgatory(image, min, max, top_down);
 	if (ret)
@@ -965,9 +965,9 @@ out:
 static Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
 					    const char *name)
 {
+	const Elf_Ehdr *ehdr;
 	Elf_Sym *syms;
 	Elf_Shdr *sechdrs;
-	Elf_Ehdr *ehdr;
 	int i, k;
 	const char *strtab;
 
_
--
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