purgatory: core purgatory functionality

Create a stand alone relocatable object purgatory which runs between two
kernels.  This name, concept and some code has been taken from
kexec-tools.  Idea is that this code runs after a crash and it runs in
minimal environment.  So keep it separate from rest of the kernel and in
long term we will have to practically do no maintenance of this code.

This code also has the logic to do verify sha256 hashes of various
segments which have been loaded into memory.  So first we verify that the
kernel we are jumping to is fine and has not been corrupted and make
progress only if checsums are verified.

This code also takes care of copying some memory contents to backup region.

[sfr@canb.auug.org.au: run host built programs from objtree]
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Greg Kroah-Hartman <greg@kroah.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: WANG Chao <chaowang@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 58 insertions, 0 deletions

diff --git a/arch/x86/purgatory/setup-x86_64.S b/arch/x86/purgatory/setup-x86_64.S
new file mode 100644
index 000000000000..fe3c91ba1bd0
--- /dev/null
+++ b/arch/x86/purgatory/setup-x86_64.S
@@ -0,0 +1,58 @@
+/*
+ * purgatory:  setup code
+ *
+ * Copyright (C) 2003,2004  Eric Biederman (ebiederm@xmission.com)
+ * Copyright (C) 2014 Red Hat Inc.
+ *
+ * This code has been taken from kexec-tools.
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2.  See the file COPYING for more details.
+ */
+
+	.text
+	.globl purgatory_start
+	.balign 16
+purgatory_start:
+	.code64
+
+	/* Load a gdt so I know what the segment registers are */
+	lgdt	gdt(%rip)
+
+	/* load the data segments */
+	movl	$0x18, %eax	/* data segment */
+	movl	%eax, %ds
+	movl	%eax, %es
+	movl	%eax, %ss
+	movl	%eax, %fs
+	movl	%eax, %gs
+
+	/* Setup a stack */
+	leaq	lstack_end(%rip), %rsp
+
+	/* Call the C code */
+	call purgatory
+	jmp	entry64
+
+	.section ".rodata"
+	.balign 16
+gdt:	/* 0x00 unusable segment
+	 * 0x08 unused
+	 * so use them as the gdt ptr
+	 */
+	.word	gdt_end - gdt - 1
+	.quad	gdt
+	.word	0, 0, 0
+
+	/* 0x10 4GB flat code segment */
+	.word	0xFFFF, 0x0000, 0x9A00, 0x00AF
+
+	/* 0x18 4GB flat data segment */
+	.word	0xFFFF, 0x0000, 0x9200, 0x00CF
+gdt_end:
+
+	.bss
+	.balign 4096
+lstack:
+	.skip 4096
+lstack_end: