kexec, x86/purgatory: Cleanup the unholy mess

[Thomas Gleixner]

The purgatory code defines global variables which are referenced via a
symbol lookup in the kexec code (core and arch).

A recent commit addressing sparse warning made these static and thereby
broke kexec file.

Why did this happen? Simply because the whole machinery is undocumented and
lacks any form of forward declarations. The variable names are unspecific
and lack a prefix, so adding forward declarations creates shadow variables
in the core code. Aside of that the code relies on magic constants and
duplicate struct definitions with no way to ensure that these things stay
in sync.

Unbreak kexec and cleanup the mess by:

 - Adding proper forward declarations and document the usage
 - Use the proper common defines instead of magic constants
 - Add a purgatory_ prefix to have a proper name space
 - Use ARRAY_SIZE() instead of a homebrewn reimplementation

Fixes: 72042a8c7b01 ("x86/purgatory: Make functions and variables static")
Reported-by: Mike Galbraith <<efault@xxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 arch/powerpc/purgatory/trampoline.S |   12 ++++++------
 arch/x86/include/asm/purgatory.h    |   20 ++++++++++++++++++++
 arch/x86/kernel/machine_kexec_64.c  |    9 ++++++---
 arch/x86/purgatory/purgatory.c      |   35 +++++++++++++++++------------------
 arch/x86/purgatory/purgatory.h      |    8 --------
 arch/x86/purgatory/setup-x86_64.S   |    2 +-
 arch/x86/purgatory/sha256.h         |    1 -
 include/linux/purgatory.h           |   23 +++++++++++++++++++++++
 kernel/kexec_file.c                 |    8 ++++----
 kernel/kexec_internal.h             |    6 +-----
 10 files changed, 78 insertions(+), 46 deletions(-)

--- a/arch/powerpc/purgatory/trampoline.S
+++ b/arch/powerpc/purgatory/trampoline.S
@@ -116,13 +116,13 @@
 
 	.data
 	.balign 8
-.globl sha256_digest
-sha256_digest:
+.globl purgatory_sha256_digest
+purgatory_sha256_digest:
 	.skip	32
-	.size sha256_digest, . - sha256_digest
+	.size purgatory_sha256_digest, . - purgatory_sha256_digest
 
 	.balign 8
-.globl sha_regions
-sha_regions:
+.globl purgatory_sha_regions
+purgatory_sha_regions:
 	.skip	8 * 2 * 16
-	.size sha_regions, . - sha_regions
+	.size purgatory_sha_regions, . - purgatory_sha_regions
--- /dev/null
+++ b/arch/x86/include/asm/purgatory.h
@@ -0,0 +1,20 @@
+#ifndef _ASM_X86_PURGATORY_H
+#define _ASM_X86_PURGATORY_H
+
+#ifndef __ASSEMBLY__
+#include <linux/purgatory.h>
+
+extern void purgatory(void);
+/*
+ * These forward declarations serve two purposes:
+ *
+ * 1) Make sparse happy when checking arch/purgatory
+ * 2) Document that these are required to be global so the symbol
+ *    lookup in kexec works
+ */
+extern unsigned long purgatory_backup_dest;
+extern unsigned long purgatory_backup_src;
+extern unsigned long purgatory_backup_sz;
+#endif	/* __ASSEMBLY__ */
+
+#endif /* _ASM_PURGATORY_H */
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -194,19 +194,22 @@ static int arch_update_purgatory(struct
 
 	/* Setup copying of backup region */
 	if (image->type == KEXEC_TYPE_CRASH) {
-		ret = kexec_purgatory_get_set_symbol(image, "backup_dest",
+		ret = kexec_purgatory_get_set_symbol(image,
+				"purgatory_backup_dest",
 				&image->arch.backup_load_addr,
 				sizeof(image->arch.backup_load_addr), 0);
 		if (ret)
 			return ret;
 
-		ret = kexec_purgatory_get_set_symbol(image, "backup_src",
+		ret = kexec_purgatory_get_set_symbol(image,
+				"purgatory_backup_src",
 				&image->arch.backup_src_start,
 				sizeof(image->arch.backup_src_start), 0);
 		if (ret)
 			return ret;
 
-		ret = kexec_purgatory_get_set_symbol(image, "backup_sz",
+		ret = kexec_purgatory_get_set_symbol(image,
+				"purgatory_backup_sz",
 				&image->arch.backup_src_sz,
 				sizeof(image->arch.backup_src_sz), 0);
 		if (ret)
--- a/arch/x86/purgatory/purgatory.c
+++ b/arch/x86/purgatory/purgatory.c
@@ -10,22 +10,19 @@
  * Version 2.  See the file COPYING for more details.
  */
 
+#include <linux/bug.h>
+#include <asm/purgatory.h>
+
 #include "sha256.h"
-#include "purgatory.h"
 #include "../boot/string.h"
 
-struct sha_region {
-	unsigned long start;
-	unsigned long len;
-};
-
-static unsigned long backup_dest;
-static unsigned long backup_src;
-static unsigned long backup_sz;
+unsigned long purgatory_backup_dest;
+unsigned long purgatory_backup_src;
+unsigned long purgatory_backup_sz;
 
-static u8 sha256_digest[SHA256_DIGEST_SIZE] = { 0 };
+u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE];
 
-struct sha_region sha_regions[16] = {};
+struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX];
 
 /*
  * On x86, second kernel requries first 640K of memory to boot. Copy
@@ -34,26 +31,28 @@ struct sha_region sha_regions[16] = {};
  */
 static int copy_backup_region(void)
 {
-	if (backup_dest)
-		memcpy((void *)backup_dest, (void *)backup_src, backup_sz);
-
+	if (purgatory_backup_dest) {
+		memcpy((void *)purgatory_backup_dest,
+		       (void *)purgatory_backup_src, purgatory_backup_sz);
+	}
 	return 0;
 }
 
 static int verify_sha256_digest(void)
 {
-	struct sha_region *ptr, *end;
+	struct kexec_sha_region *ptr, *end;
 	u8 digest[SHA256_DIGEST_SIZE];
 	struct sha256_state sctx;
 
 	sha256_init(&sctx);
-	end = &sha_regions[sizeof(sha_regions)/sizeof(sha_regions[0])];
-	for (ptr = sha_regions; ptr < end; ptr++)
+	end = purgatory_sha_regions + ARRAY_SIZE(purgatory_sha_regions);
+
+	for (ptr = purgatory_sha_regions; ptr < end; ptr++)
 		sha256_update(&sctx, (uint8_t *)(ptr->start), ptr->len);
 
 	sha256_final(&sctx, digest);
 
-	if (memcmp(digest, sha256_digest, sizeof(digest)))
+	if (memcmp(digest, purgatory_sha256_digest, sizeof(digest)))
 		return 1;
 
 	return 0;
--- a/arch/x86/purgatory/purgatory.h
+++ /dev/null
@@ -1,8 +0,0 @@
-#ifndef PURGATORY_H
-#define PURGATORY_H
-
-#ifndef __ASSEMBLY__
-extern void purgatory(void);
-#endif	/* __ASSEMBLY__ */
-
-#endif /* PURGATORY_H */
--- a/arch/x86/purgatory/setup-x86_64.S
+++ b/arch/x86/purgatory/setup-x86_64.S
@@ -9,7 +9,7 @@
  * This source code is licensed under the GNU General Public License,
  * Version 2.  See the file COPYING for more details.
  */
-#include "purgatory.h"
+#include <asm/purgatory.h>
 
 	.text
 	.globl purgatory_start
--- a/arch/x86/purgatory/sha256.h
+++ b/arch/x86/purgatory/sha256.h
@@ -10,7 +10,6 @@
 #ifndef SHA256_H
 #define SHA256_H
 
-
 #include <linux/types.h>
 #include <crypto/sha.h>
 
--- /dev/null
+++ b/include/linux/purgatory.h
@@ -0,0 +1,23 @@
+#ifndef _LINUX_PURGATORY_H
+#define _LINUX_PURGATORY_H
+
+#include <linux/types.h>
+#include <crypto/sha.h>
+#include <uapi/linux/kexec.h>
+
+struct kexec_sha_region {
+	unsigned long start;
+	unsigned long len;
+};
+
+/*
+ * These forward declarations serve two purposes:
+ *
+ * 1) Make sparse happy when checking arch/purgatory
+ * 2) Document that these are required to be global so the symbol
+ *    lookup in kexec works
+ */
+extern struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX];
+extern u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE];
+
+#endif
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -614,13 +614,13 @@ static int kexec_calculate_store_digests
 		ret = crypto_shash_final(desc, digest);
 		if (ret)
 			goto out_free_digest;
-		ret = kexec_purgatory_get_set_symbol(image, "sha_regions",
-						sha_regions, sha_region_sz, 0);
+		ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha_regions",
+						     sha_regions, sha_region_sz, 0);
 		if (ret)
 			goto out_free_digest;
 
-		ret = kexec_purgatory_get_set_symbol(image, "sha256_digest",
-						digest, SHA256_DIGEST_SIZE, 0);
+		ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha256_digest",
+						     digest, SHA256_DIGEST_SIZE, 0);
 		if (ret)
 			goto out_free_digest;
 	}
--- a/kernel/kexec_internal.h
+++ b/kernel/kexec_internal.h
@@ -15,11 +15,7 @@ int kimage_is_destination_range(struct k
 extern struct mutex kexec_mutex;
 
 #ifdef CONFIG_KEXEC_FILE
-struct kexec_sha_region {
-	unsigned long start;
-	unsigned long len;
-};
-
+#include <linux/purgatory.h>
 void kimage_file_post_load_cleanup(struct kimage *image);
 #else /* CONFIG_KEXEC_FILE */
 static inline void kimage_file_post_load_cleanup(struct kimage *image) { }