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linux-stable/arch/x86/kernel/head_64.S
Michael Roth cea750c99d x86/head/64: Re-enable stack protection 
commit 469693d8f6 upstream.

Due to

  103a4908ad ("x86/head/64: Disable stack protection for head$(BITS).o")

kernel/head{32,64}.c are compiled with -fno-stack-protector to allow
a call to set_bringup_idt_handler(), which would otherwise have stack
protection enabled with CONFIG_STACKPROTECTOR_STRONG.

While sufficient for that case, there may still be issues with calls to
any external functions that were compiled with stack protection enabled
that in-turn make stack-protected calls, or if the exception handlers
set up by set_bringup_idt_handler() make calls to stack-protected
functions.

Subsequent patches for SEV-SNP CPUID validation support will introduce
both such cases. Attempting to disable stack protection for everything
in scope to address that is prohibitive since much of the code, like the
SEV-ES #VC handler, is shared code that remains in use after boot and
could benefit from having stack protection enabled. Attempting to inline
calls is brittle and can quickly balloon out to library/helper code
where that's not really an option.

Instead, re-enable stack protection for head32.c/head64.c, and make the
appropriate changes to ensure the segment used for the stack canary is
initialized in advance of any stack-protected C calls.

For head64.c:

- The BSP will enter from startup_64() and call into C code
  (startup_64_setup_env()) shortly after setting up the stack, which
  may result in calls to stack-protected code. Set up %gs early to allow
  for this safely.
- APs will enter from secondary_startup_64*(), and %gs will be set up
  soon after. There is one call to C code prior to %gs being setup
  (__startup_secondary_64()), but it is only to fetch 'sme_me_mask'
  global, so just load 'sme_me_mask' directly instead, and remove the
  now-unused __startup_secondary_64() function.

For head32.c:

- BSPs/APs will set %fs to __BOOT_DS prior to any C calls. In recent
  kernels, the compiler is configured to access the stack canary at
  %fs:__stack_chk_guard [1], which overlaps with the initial per-cpu
  '__stack_chk_guard' variable in the initial/"master" .data..percpu
  area. This is sufficient to allow access to the canary for use
  during initial startup, so no changes are needed there.

[1] 3fb0fdb3bb ("x86/stackprotector/32: Make the canary into a regular percpu variable")

  [ bp: Massage commit message. ]

Suggested-by: Joerg Roedel <jroedel@suse.de> #for 64-bit %gs set up
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-24-brijesh.singh@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2024-04-13 12:59:58 +02:00

621 lines
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/* SPDX-License-Identifier: GPL-2.0 */
/*
* linux/arch/x86/kernel/head_64.S -- start in 32bit and switch to 64bit
*
* Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
* Copyright (C) 2000 Pavel Machek <pavel@suse.cz>
* Copyright (C) 2000 Karsten Keil <kkeil@suse.de>
* Copyright (C) 2001,2002 Andi Kleen <ak@suse.de>
* Copyright (C) 2005 Eric Biederman <ebiederm@xmission.com>
*/
#include <linux/linkage.h>
#include <linux/threads.h>
#include <linux/init.h>
#include <linux/pgtable.h>
#include <asm/segment.h>
#include <asm/page.h>
#include <asm/msr.h>
#include <asm/cache.h>
#include <asm/processor-flags.h>
#include <asm/percpu.h>
#include <asm/nops.h>
#include "../entry/calling.h"
#include <asm/export.h>
#include <asm/nospec-branch.h>
#include <asm/fixmap.h>
#ifdef CONFIG_PARAVIRT_XXL
#include <asm/asm-offsets.h>
#include <asm/paravirt.h>
#define GET_CR2_INTO(reg) GET_CR2_INTO_AX ; _ASM_MOV %_ASM_AX, reg
#else
#define INTERRUPT_RETURN iretq
#define GET_CR2_INTO(reg) _ASM_MOV %cr2, reg
#endif
/*
* We are not able to switch in one step to the final KERNEL ADDRESS SPACE
* because we need identity-mapped pages.
*/
#define l4_index(x) (((x) >> 39) & 511)
#define pud_index(x) (((x) >> PUD_SHIFT) & (PTRS_PER_PUD-1))
L4_PAGE_OFFSET = l4_index(__PAGE_OFFSET_BASE_L4)
L4_START_KERNEL = l4_index(__START_KERNEL_map)
L3_START_KERNEL = pud_index(__START_KERNEL_map)
.text
__HEAD
.code64
SYM_CODE_START_NOALIGN(startup_64)
UNWIND_HINT_EMPTY
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
* and someone has loaded an identity mapped page table
* for us. These identity mapped page tables map all of the
* kernel pages and possibly all of memory.
*
* %rsi holds a physical pointer to real_mode_data.
*
* We come here either directly from a 64bit bootloader, or from
* arch/x86/boot/compressed/head_64.S.
*
* We only come here initially at boot nothing else comes here.
*
* Since we may be loaded at an address different from what we were
* compiled to run at we first fixup the physical addresses in our page
* tables and then reload them.
*/
/* Set up the stack for verify_cpu(), similar to initial_stack below */
leaq (__end_init_task - SIZEOF_PTREGS)(%rip), %rsp
leaq _text(%rip), %rdi
/*
* initial_gs points to initial fixed_percpu_data struct with storage for
* the stack protector canary. Global pointer fixups are needed at this
* stage, so apply them as is done in fixup_pointer(), and initialize %gs
* such that the canary can be accessed at %gs:40 for subsequent C calls.
*/
movl $MSR_GS_BASE, %ecx
movq initial_gs(%rip), %rax
movq $_text, %rdx
subq %rdx, %rax
addq %rdi, %rax
movq %rax, %rdx
shrq $32, %rdx
wrmsr
pushq %rsi
call startup_64_setup_env
popq %rsi
/* Now switch to __KERNEL_CS so IRET works reliably */
pushq $__KERNEL_CS
leaq .Lon_kernel_cs(%rip), %rax
pushq %rax
lretq
.Lon_kernel_cs:
UNWIND_HINT_EMPTY
/* Sanitize CPU configuration */
call verify_cpu
/*
* Perform pagetable fixups. Additionally, if SME is active, encrypt
* the kernel and retrieve the modifier (SME encryption mask if SME
* is active) to be added to the initial pgdir entry that will be
* programmed into CR3.
*/
leaq _text(%rip), %rdi
pushq %rsi
call __startup_64
popq %rsi
/* Form the CR3 value being sure to include the CR3 modifier */
addq $(early_top_pgt - __START_KERNEL_map), %rax
jmp 1f
SYM_CODE_END(startup_64)
SYM_CODE_START(secondary_startup_64)
UNWIND_HINT_EMPTY
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
* and someone has loaded a mapped page table.
*
* %rsi holds a physical pointer to real_mode_data.
*
* We come here either from startup_64 (using physical addresses)
* or from trampoline.S (using virtual addresses).
*
* Using virtual addresses from trampoline.S removes the need
* to have any identity mapped pages in the kernel page table
* after the boot processor executes this code.
*/
/* Sanitize CPU configuration */
call verify_cpu
/*
* The secondary_startup_64_no_verify entry point is only used by
* SEV-ES guests. In those guests the call to verify_cpu() would cause
* #VC exceptions which can not be handled at this stage of secondary
* CPU bringup.
*
* All non SEV-ES systems, especially Intel systems, need to execute
* verify_cpu() above to make sure NX is enabled.
*/
SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
UNWIND_HINT_EMPTY
/*
* Retrieve the modifier (SME encryption mask if SME is active) to be
* added to the initial pgdir entry that will be programmed into CR3.
*/
#ifdef CONFIG_AMD_MEM_ENCRYPT
movq sme_me_mask, %rax
#else
xorq %rax, %rax
#endif
/* Form the CR3 value being sure to include the CR3 modifier */
addq $(init_top_pgt - __START_KERNEL_map), %rax
1:
/* Enable PAE mode, PGE and LA57 */
movl $(X86_CR4_PAE | X86_CR4_PGE), %ecx
#ifdef CONFIG_X86_5LEVEL
testl $1, __pgtable_l5_enabled(%rip)
jz 1f
orl $X86_CR4_LA57, %ecx
1:
#endif
movq %rcx, %cr4
/* Setup early boot stage 4-/5-level pagetables. */
addq phys_base(%rip), %rax
/*
* For SEV guests: Verify that the C-bit is correct. A malicious
* hypervisor could lie about the C-bit position to perform a ROP
* attack on the guest by writing to the unencrypted stack and wait for
* the next RET instruction.
* %rsi carries pointer to realmode data and is callee-clobbered. Save
* and restore it.
*/
pushq %rsi
movq %rax, %rdi
call sev_verify_cbit
popq %rsi
/* Switch to new page-table */
movq %rax, %cr3
/* Ensure I am executing from virtual addresses */
movq $1f, %rax
ANNOTATE_RETPOLINE_SAFE
jmp *%rax
1:
UNWIND_HINT_EMPTY
/*
* We must switch to a new descriptor in kernel space for the GDT
* because soon the kernel won't have access anymore to the userspace
* addresses where we're currently running on. We have to do that here
* because in 32bit we couldn't load a 64bit linear address.
*/
lgdt early_gdt_descr(%rip)
/* set up data segments */
xorl %eax,%eax
movl %eax,%ds
movl %eax,%ss
movl %eax,%es
/*
* We don't really need to load %fs or %gs, but load them anyway
* to kill any stale realmode selectors. This allows execution
* under VT hardware.
*/
movl %eax,%fs
movl %eax,%gs
/* Set up %gs.
*
* The base of %gs always points to fixed_percpu_data. If the
* stack protector canary is enabled, it is located at %gs:40.
* Note that, on SMP, the boot cpu uses init data section until
* the per cpu areas are set up.
*/
movl $MSR_GS_BASE,%ecx
movl initial_gs(%rip),%eax
movl initial_gs+4(%rip),%edx
wrmsr
/*
* Setup a boot time stack - Any secondary CPU will have lost its stack
* by now because the cr3-switch above unmaps the real-mode stack
*/
movq initial_stack(%rip), %rsp
/* Setup and Load IDT */
pushq %rsi
call early_setup_idt
popq %rsi
/* Check if nx is implemented */
movl $0x80000001, %eax
cpuid
movl %edx,%edi
/* Setup EFER (Extended Feature Enable Register) */
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_SCE, %eax /* Enable System Call */
btl $20,%edi /* No Execute supported? */
jnc 1f
btsl $_EFER_NX, %eax
btsq $_PAGE_BIT_NX,early_pmd_flags(%rip)
1: wrmsr /* Make changes effective */
/* Setup cr0 */
movl $CR0_STATE, %eax
/* Make changes effective */
movq %rax, %cr0
/* zero EFLAGS after setting rsp */
pushq $0
popfq
/* rsi is pointer to real mode structure with interesting info.
pass it to C */
movq %rsi, %rdi
.Ljump_to_C_code:
/*
* Jump to run C code and to be on a real kernel address.
* Since we are running on identity-mapped space we have to jump
* to the full 64bit address, this is only possible as indirect
* jump. In addition we need to ensure %cs is set so we make this
* a far return.
*
* Note: do not change to far jump indirect with 64bit offset.
*
* AMD does not support far jump indirect with 64bit offset.
* AMD64 Architecture Programmer's Manual, Volume 3: states only
* JMP FAR mem16:16 FF /5 Far jump indirect,
* with the target specified by a far pointer in memory.
* JMP FAR mem16:32 FF /5 Far jump indirect,
* with the target specified by a far pointer in memory.
*
* Intel64 does support 64bit offset.
* Software Developer Manual Vol 2: states:
* FF /5 JMP m16:16 Jump far, absolute indirect,
* address given in m16:16
* FF /5 JMP m16:32 Jump far, absolute indirect,
* address given in m16:32.
* REX.W + FF /5 JMP m16:64 Jump far, absolute indirect,
* address given in m16:64.
*/
pushq $.Lafter_lret # put return address on stack for unwinder
xorl %ebp, %ebp # clear frame pointer
movq initial_code(%rip), %rax
pushq $__KERNEL_CS # set correct cs
pushq %rax # target address in negative space
lretq
.Lafter_lret:
SYM_CODE_END(secondary_startup_64)
#include "verify_cpu.S"
#include "sev_verify_cbit.S"
#ifdef CONFIG_HOTPLUG_CPU
/*
* Boot CPU0 entry point. It's called from play_dead(). Everything has been set
* up already except stack. We just set up stack here. Then call
* start_secondary() via .Ljump_to_C_code.
*/
SYM_CODE_START(start_cpu0)
UNWIND_HINT_EMPTY
movq initial_stack(%rip), %rsp
jmp .Ljump_to_C_code
SYM_CODE_END(start_cpu0)
#endif
#ifdef CONFIG_AMD_MEM_ENCRYPT
/*
* VC Exception handler used during early boot when running on kernel
* addresses, but before the switch to the idt_table can be made.
* The early_idt_handler_array can't be used here because it calls into a lot
* of __init code and this handler is also used during CPU offlining/onlining.
* Therefore this handler ends up in the .text section so that it stays around
* when .init.text is freed.
*/
SYM_CODE_START_NOALIGN(vc_boot_ghcb)
UNWIND_HINT_IRET_REGS offset=8
ANNOTATE_UNRET_END
/* Build pt_regs */
PUSH_AND_CLEAR_REGS
/* Call C handler */
movq %rsp, %rdi
movq ORIG_RAX(%rsp), %rsi
movq initial_vc_handler(%rip), %rax
ANNOTATE_RETPOLINE_SAFE
call *%rax
/* Unwind pt_regs */
POP_REGS
/* Remove Error Code */
addq $8, %rsp
/* Pure iret required here - don't use INTERRUPT_RETURN */
iretq
SYM_CODE_END(vc_boot_ghcb)
#endif
/* Both SMP bootup and ACPI suspend change these variables */
__REFDATA
.balign 8
SYM_DATA(initial_code, .quad x86_64_start_kernel)
SYM_DATA(initial_gs, .quad INIT_PER_CPU_VAR(fixed_percpu_data))
#ifdef CONFIG_AMD_MEM_ENCRYPT
SYM_DATA(initial_vc_handler, .quad handle_vc_boot_ghcb)
#endif
/*
* The SIZEOF_PTREGS gap is a convention which helps the in-kernel unwinder
* reliably detect the end of the stack.
*/
SYM_DATA(initial_stack, .quad init_thread_union + THREAD_SIZE - SIZEOF_PTREGS)
__FINITDATA
__INIT
SYM_CODE_START(early_idt_handler_array)
i = 0
.rept NUM_EXCEPTION_VECTORS
.if ((EXCEPTION_ERRCODE_MASK >> i) & 1) == 0
UNWIND_HINT_IRET_REGS
pushq $0 # Dummy error code, to make stack frame uniform
.else
UNWIND_HINT_IRET_REGS offset=8
.endif
pushq $i # 72(%rsp) Vector number
jmp early_idt_handler_common
UNWIND_HINT_IRET_REGS
i = i + 1
.fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
.endr
UNWIND_HINT_IRET_REGS offset=16
SYM_CODE_END(early_idt_handler_array)
SYM_CODE_START_LOCAL(early_idt_handler_common)
ANNOTATE_UNRET_END
/*
* The stack is the hardware frame, an error code or zero, and the
* vector number.
*/
cld
incl early_recursion_flag(%rip)
/* The vector number is currently in the pt_regs->di slot. */
pushq %rsi /* pt_regs->si */
movq 8(%rsp), %rsi /* RSI = vector number */
movq %rdi, 8(%rsp) /* pt_regs->di = RDI */
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq %rax /* pt_regs->ax */
pushq %r8 /* pt_regs->r8 */
pushq %r9 /* pt_regs->r9 */
pushq %r10 /* pt_regs->r10 */
pushq %r11 /* pt_regs->r11 */
pushq %rbx /* pt_regs->bx */
pushq %rbp /* pt_regs->bp */
pushq %r12 /* pt_regs->r12 */
pushq %r13 /* pt_regs->r13 */
pushq %r14 /* pt_regs->r14 */
pushq %r15 /* pt_regs->r15 */
UNWIND_HINT_REGS
movq %rsp,%rdi /* RDI = pt_regs; RSI is already trapnr */
call do_early_exception
decl early_recursion_flag(%rip)
jmp restore_regs_and_return_to_kernel
SYM_CODE_END(early_idt_handler_common)
#ifdef CONFIG_AMD_MEM_ENCRYPT
/*
* VC Exception handler used during very early boot. The
* early_idt_handler_array can't be used because it returns via the
* paravirtualized INTERRUPT_RETURN and pv-ops don't work that early.
*
* This handler will end up in the .init.text section and not be
* available to boot secondary CPUs.
*/
SYM_CODE_START_NOALIGN(vc_no_ghcb)
UNWIND_HINT_IRET_REGS offset=8
ANNOTATE_UNRET_END
/* Build pt_regs */
PUSH_AND_CLEAR_REGS
/* Call C handler */
movq %rsp, %rdi
movq ORIG_RAX(%rsp), %rsi
call do_vc_no_ghcb
/* Unwind pt_regs */
POP_REGS
/* Remove Error Code */
addq $8, %rsp
/* Pure iret required here - don't use INTERRUPT_RETURN */
iretq
SYM_CODE_END(vc_no_ghcb)
#endif
#define SYM_DATA_START_PAGE_ALIGNED(name) \
SYM_START(name, SYM_L_GLOBAL, .balign PAGE_SIZE)
#ifdef CONFIG_PAGE_TABLE_ISOLATION
/*
* Each PGD needs to be 8k long and 8k aligned. We do not
* ever go out to userspace with these, so we do not
* strictly *need* the second page, but this allows us to
* have a single set_pgd() implementation that does not
* need to worry about whether it has 4k or 8k to work
* with.
*
* This ensures PGDs are 8k long:
*/
#define PTI_USER_PGD_FILL 512
/* This ensures they are 8k-aligned: */
#define SYM_DATA_START_PTI_ALIGNED(name) \
SYM_START(name, SYM_L_GLOBAL, .balign 2 * PAGE_SIZE)
#else
#define SYM_DATA_START_PTI_ALIGNED(name) \
SYM_DATA_START_PAGE_ALIGNED(name)
#define PTI_USER_PGD_FILL 0
#endif
/* Automate the creation of 1 to 1 mapping pmd entries */
#define PMDS(START, PERM, COUNT) \
i = 0 ; \
.rept (COUNT) ; \
.quad (START) + (i << PMD_SHIFT) + (PERM) ; \
i = i + 1 ; \
.endr
__INITDATA
.balign 4
SYM_DATA_START_PTI_ALIGNED(early_top_pgt)
.fill 512,8,0
.fill PTI_USER_PGD_FILL,8,0
SYM_DATA_END(early_top_pgt)
SYM_DATA_START_PAGE_ALIGNED(early_dynamic_pgts)
.fill 512*EARLY_DYNAMIC_PAGE_TABLES,8,0
SYM_DATA_END(early_dynamic_pgts)
SYM_DATA(early_recursion_flag, .long 0)
.data
#if defined(CONFIG_XEN_PV) || defined(CONFIG_PVH)
SYM_DATA_START_PTI_ALIGNED(init_top_pgt)
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.org init_top_pgt + L4_PAGE_OFFSET*8, 0
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.org init_top_pgt + L4_START_KERNEL*8, 0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
.quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
.fill PTI_USER_PGD_FILL,8,0
SYM_DATA_END(init_top_pgt)
SYM_DATA_START_PAGE_ALIGNED(level3_ident_pgt)
.quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.fill 511, 8, 0
SYM_DATA_END(level3_ident_pgt)
SYM_DATA_START_PAGE_ALIGNED(level2_ident_pgt)
/*
* Since I easily can, map the first 1G.
* Don't set NX because code runs from these pages.
*
* Note: This sets _PAGE_GLOBAL despite whether
* the CPU supports it or it is enabled. But,
* the CPU should ignore the bit.
*/
PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD)
SYM_DATA_END(level2_ident_pgt)
#else
SYM_DATA_START_PTI_ALIGNED(init_top_pgt)
.fill 512,8,0
.fill PTI_USER_PGD_FILL,8,0
SYM_DATA_END(init_top_pgt)
#endif
#ifdef CONFIG_X86_5LEVEL
SYM_DATA_START_PAGE_ALIGNED(level4_kernel_pgt)
.fill 511,8,0
.quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
SYM_DATA_END(level4_kernel_pgt)
#endif
SYM_DATA_START_PAGE_ALIGNED(level3_kernel_pgt)
.fill L3_START_KERNEL,8,0
/* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */
.quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
SYM_DATA_END(level3_kernel_pgt)
SYM_DATA_START_PAGE_ALIGNED(level2_kernel_pgt)
/*
* 512 MB kernel mapping. We spend a full page on this pagetable
* anyway.
*
* The kernel code+data+bss must not be bigger than that.
*
* (NOTE: at +512MB starts the module area, see MODULES_VADDR.
* If you want to increase this then increase MODULES_VADDR
* too.)
*
* This table is eventually used by the kernel during normal
* runtime. Care must be taken to clear out undesired bits
* later, like _PAGE_RW or _PAGE_GLOBAL in some cases.
*/
PMDS(0, __PAGE_KERNEL_LARGE_EXEC,
KERNEL_IMAGE_SIZE/PMD_SIZE)
SYM_DATA_END(level2_kernel_pgt)
SYM_DATA_START_PAGE_ALIGNED(level2_fixmap_pgt)
.fill (512 - 4 - FIXMAP_PMD_NUM),8,0
pgtno = 0
.rept (FIXMAP_PMD_NUM)
.quad level1_fixmap_pgt + (pgtno << PAGE_SHIFT) - __START_KERNEL_map \
+ _PAGE_TABLE_NOENC;
pgtno = pgtno + 1
.endr
/* 6 MB reserved space + a 2MB hole */
.fill 4,8,0
SYM_DATA_END(level2_fixmap_pgt)
SYM_DATA_START_PAGE_ALIGNED(level1_fixmap_pgt)
.rept (FIXMAP_PMD_NUM)
.fill 512,8,0
.endr
SYM_DATA_END(level1_fixmap_pgt)
#undef PMDS
.data
.align 16
SYM_DATA(early_gdt_descr, .word GDT_ENTRIES*8-1)
SYM_DATA_LOCAL(early_gdt_descr_base, .quad INIT_PER_CPU_VAR(gdt_page))
.align 16
/* This must match the first entry in level2_kernel_pgt */
SYM_DATA(phys_base, .quad 0x0)
EXPORT_SYMBOL(phys_base)
#include "../../x86/xen/xen-head.S"
__PAGE_ALIGNED_BSS
SYM_DATA_START_PAGE_ALIGNED(empty_zero_page)
.skip PAGE_SIZE
SYM_DATA_END(empty_zero_page)
EXPORT_SYMBOL(empty_zero_page)
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