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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. [[email protected]: run host built programs from objtree] Signed-off-by: Vivek Goyal <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Michael Kerrisk <[email protected]> Cc: Yinghai Lu <[email protected]> Cc: Eric Biederman <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Matthew Garrett <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: Dave Young <[email protected]> Cc: WANG Chao <[email protected]> Cc: Baoquan He <[email protected]> Cc: Andy Lutomirski <[email protected]> Signed-off-by: Stephen Rothwell <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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‎arch/x86/Kbuild

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@@ -16,3 +16,7 @@ obj-$(CONFIG_IA32_EMULATION) += ia32/
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obj-y += platform/
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obj-y += net/
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ifeq ($(CONFIG_X86_64),y)
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obj-$(CONFIG_KEXEC) += purgatory/
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endif

‎arch/x86/Makefile

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@@ -183,6 +183,14 @@ archscripts: scripts_basic
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archheaders:
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$(Q)$(MAKE) $(build)=arch/x86/syscalls all
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archprepare:
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ifeq ($(CONFIG_KEXEC),y)
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# Build only for 64bit. No loaders for 32bit yet.
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ifeq ($(CONFIG_X86_64),y)
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$(Q)$(MAKE) $(build)=arch/x86/purgatory arch/x86/purgatory/kexec-purgatory.c
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endif
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endif
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###
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# Kernel objects
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‎arch/x86/purgatory/Makefile

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purgatory-y := purgatory.o stack.o setup-x86_$(BITS).o sha256.o entry64.o string.o
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targets += $(purgatory-y)
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PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
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LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
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targets += purgatory.ro
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# Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
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# in turn leaves some undefined symbols like __fentry__ in purgatory and not
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# sure how to relocate those. Like kexec-tools, use custom flags.
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KBUILD_CFLAGS := -fno-strict-aliasing -Wall -Wstrict-prototypes -fno-zero-initialized-in-bss -fno-builtin -ffreestanding -c -MD -Os -mcmodel=large
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$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
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$(call if_changed,ld)
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targets += kexec-purgatory.c
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quiet_cmd_bin2c = BIN2C $@
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cmd_bin2c = cat $(obj)/purgatory.ro | $(objtree)/scripts/basic/bin2c kexec_purgatory > $(obj)/kexec-purgatory.c
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$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro FORCE
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$(call if_changed,bin2c)
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# No loaders for 32bits yet.
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ifeq ($(CONFIG_X86_64),y)
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obj-$(CONFIG_KEXEC) += kexec-purgatory.o
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endif

‎arch/x86/purgatory/entry64.S

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/*
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* Copyright (C) 2003,2004 Eric Biederman ([email protected])
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* Copyright (C) 2014 Red Hat Inc.
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* Author(s): Vivek Goyal <[email protected]>
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*
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* This code has been taken from kexec-tools.
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*
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* This source code is licensed under the GNU General Public License,
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* Version 2. See the file COPYING for more details.
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*/
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.text
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.balign 16
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.code64
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.globl entry64, entry64_regs
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entry64:
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/* Setup a gdt that should be preserved */
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lgdt gdt(%rip)
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/* load the data segments */
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movl $0x18, %eax /* data segment */
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movl %eax, %ds
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movl %eax, %es
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movl %eax, %ss
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movl %eax, %fs
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movl %eax, %gs
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/* Setup new stack */
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leaq stack_init(%rip), %rsp
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pushq $0x10 /* CS */
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leaq new_cs_exit(%rip), %rax
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pushq %rax
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lretq
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new_cs_exit:
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/* Load the registers */
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movq rax(%rip), %rax
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movq rbx(%rip), %rbx
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movq rcx(%rip), %rcx
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movq rdx(%rip), %rdx
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movq rsi(%rip), %rsi
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movq rdi(%rip), %rdi
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movq rsp(%rip), %rsp
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movq rbp(%rip), %rbp
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movq r8(%rip), %r8
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movq r9(%rip), %r9
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movq r10(%rip), %r10
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movq r11(%rip), %r11
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movq r12(%rip), %r12
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movq r13(%rip), %r13
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movq r14(%rip), %r14
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movq r15(%rip), %r15
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/* Jump to the new code... */
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jmpq *rip(%rip)
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.section ".rodata"
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.balign 4
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entry64_regs:
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rax: .quad 0x0
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rbx: .quad 0x0
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rcx: .quad 0x0
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rdx: .quad 0x0
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rsi: .quad 0x0
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rdi: .quad 0x0
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rsp: .quad 0x0
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rbp: .quad 0x0
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r8: .quad 0x0
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r9: .quad 0x0
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r10: .quad 0x0
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r11: .quad 0x0
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r12: .quad 0x0
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r13: .quad 0x0
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r14: .quad 0x0
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r15: .quad 0x0
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rip: .quad 0x0
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.size entry64_regs, . - entry64_regs
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/* GDT */
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.section ".rodata"
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.balign 16
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gdt:
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/* 0x00 unusable segment
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* 0x08 unused
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* so use them as gdt ptr
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*/
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.word gdt_end - gdt - 1
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.quad gdt
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.word 0, 0, 0
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/* 0x10 4GB flat code segment */
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.word 0xFFFF, 0x0000, 0x9A00, 0x00AF
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/* 0x18 4GB flat data segment */
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.word 0xFFFF, 0x0000, 0x9200, 0x00CF
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gdt_end:
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stack: .quad 0, 0
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stack_init:

‎arch/x86/purgatory/purgatory.c

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/*
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* purgatory: Runs between two kernels
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*
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* Copyright (C) 2014 Red Hat Inc.
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*
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* Author:
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* Vivek Goyal <[email protected]>
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*
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* This source code is licensed under the GNU General Public License,
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* Version 2. See the file COPYING for more details.
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*/
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#include "sha256.h"
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#include "../boot/string.h"
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struct sha_region {
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unsigned long start;
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unsigned long len;
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};
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unsigned long backup_dest = 0;
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unsigned long backup_src = 0;
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unsigned long backup_sz = 0;
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u8 sha256_digest[SHA256_DIGEST_SIZE] = { 0 };
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struct sha_region sha_regions[16] = {};
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/*
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* On x86, second kernel requries first 640K of memory to boot. Copy
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* first 640K to a backup region in reserved memory range so that second
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* kernel can use first 640K.
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*/
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static int copy_backup_region(void)
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{
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if (backup_dest)
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memcpy((void *)backup_dest, (void *)backup_src, backup_sz);
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return 0;
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}
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int verify_sha256_digest(void)
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{
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struct sha_region *ptr, *end;
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u8 digest[SHA256_DIGEST_SIZE];
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struct sha256_state sctx;
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sha256_init(&sctx);
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end = &sha_regions[sizeof(sha_regions)/sizeof(sha_regions[0])];
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for (ptr = sha_regions; ptr < end; ptr++)
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sha256_update(&sctx, (uint8_t *)(ptr->start), ptr->len);
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sha256_final(&sctx, digest);
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if (memcmp(digest, sha256_digest, sizeof(digest)))
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return 1;
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return 0;
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}
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void purgatory(void)
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{
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int ret;
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ret = verify_sha256_digest();
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if (ret) {
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/* loop forever */
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for (;;)
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;
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}
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copy_backup_region();
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}

‎arch/x86/purgatory/setup-x86_64.S

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

‎arch/x86/purgatory/stack.S

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/*
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* purgatory: stack
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*
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* Copyright (C) 2014 Red Hat Inc.
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*
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* This source code is licensed under the GNU General Public License,
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* Version 2. See the file COPYING for more details.
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*/
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/* A stack for the loaded kernel.
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* Seperate and in the data section so it can be prepopulated.
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*/
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.data
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.balign 4096
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.globl stack, stack_end
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stack:
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.skip 4096
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stack_end:

‎arch/x86/purgatory/string.c

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/*
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* Simple string functions.
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*
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* Copyright (C) 2014 Red Hat Inc.
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*
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* Author:
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* Vivek Goyal <[email protected]>
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*
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* This source code is licensed under the GNU General Public License,
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* Version 2. See the file COPYING for more details.
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*/
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#include "../boot/string.c"

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