linux-kernel - [PATCH 03/11] kexec_file: Make purgatory

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Date:   Mon, 26 Feb 2018 16:16:12 +0100
From:   Philipp Rudo <prudo@...ux.vnet.ibm.com>
To:     kexec@...ts.infradead.org, linux-s390@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Dave Young <dyoung@...hat.com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>
Subject: [PATCH 03/11] kexec_file: 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.

Signed-off-by: Philipp Rudo <prudo@...ux.vnet.ibm.com>
---
 include/linux/kexec.h | 17 +++++++++++------
 kernel/kexec_file.c   |  4 ++--
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 7bae5e87bf0d..10842eece180 100644
--- a/include/linux/kexec.h
+++ b/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 --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 0f044457b40c..06fc9fdd2474 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -880,7 +880,7 @@ int kexec_load_purgatory(struct kimage *image, unsigned long min,
 	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)
@@ -904,9 +904,9 @@ int kexec_load_purgatory(struct kimage *image, unsigned long min,
 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;
 
-- 
2.13.5