x86, selftests: Add a test for the "sysret_ss_attrs" bug
On AMD CPUs, SYSRET can return with a valid SS descriptor with
with the hidden attributes set to an unusable state. Make sure
the kernel doesn't let this happen. This detects an
as-yet-unfixed regression.
Note that the 64-bit version of this test fails on AMD CPUs on
all kernel versions, although the issue in the 64-bit case is
much less severe than in the 32-bit case.
Reported-by: Brian Gerst <brgerst@gmail.com>
Tested-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Tests: e7d6eefaaa ("x86/vdso32/syscall.S: Do not load __USER32_DS to %ss")
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/resend_4d740841bac383742949e2fefb03982736595087.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski
Ingo Molnar
parent
7ae383be81
commit
e22438f8e9
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@ -1,6 +1,6 @@
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.PHONY: all all_32 all_64 check_build32 clean run_tests
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TARGETS_C_BOTHBITS := sigreturn single_step_syscall
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TARGETS_C_BOTHBITS := sigreturn single_step_syscall sysret_ss_attrs
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BINARIES_32 := $(TARGETS_C_BOTHBITS:%=%_32)
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BINARIES_64 := $(TARGETS_C_BOTHBITS:%=%_64)
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@ -46,3 +46,6 @@ check_build32:
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echo " yum install glibc-devel.*i686"; \
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exit 1; \
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fi
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# Some tests have additional dependencies.
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sysret_ss_attrs_64: thunks.S
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@ -4,10 +4,12 @@
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# script here.
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./sigreturn_32 || exit 1
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./single_step_syscall_32 || exit 1
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./sysret_ss_attrs_32 || exit 1
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if [[ "$uname -p" -eq "x86_64" ]]; then
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./sigreturn_64 || exit 1
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./single_step_syscall_64 || exit 1
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./sysret_ss_attrs_64 || exit 1
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fi
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exit 0
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@ -0,0 +1,112 @@
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/*
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* sysret_ss_attrs.c - test that syscalls return valid hidden SS attributes
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* Copyright (c) 2015 Andrew Lutomirski
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms and conditions of the GNU General Public License,
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* version 2, as published by the Free Software Foundation.
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*
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* This program is distributed in the hope it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* On AMD CPUs, SYSRET can return with a valid SS descriptor with with
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* the hidden attributes set to an unusable state. Make sure the kernel
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* doesn't let this happen.
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*/
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#define _GNU_SOURCE
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#include <stdlib.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <err.h>
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#include <stddef.h>
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#include <stdbool.h>
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#include <pthread.h>
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static void *threadproc(void *ctx)
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{
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/*
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* Do our best to cause sleeps on this CPU to exit the kernel and
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* re-enter with SS = 0.
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*/
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while (true)
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;
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return NULL;
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}
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#ifdef __x86_64__
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extern unsigned long call32_from_64(void *stack, void (*function)(void));
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asm (".pushsection .text\n\t"
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".code32\n\t"
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"test_ss:\n\t"
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"pushl $0\n\t"
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"popl %eax\n\t"
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"ret\n\t"
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".code64");
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extern void test_ss(void);
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#endif
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int main()
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{
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/*
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* Start a busy-looping thread on the same CPU we're on.
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* For simplicity, just stick everything to CPU 0. This will
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* fail in some containers, but that's probably okay.
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*/
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cpu_set_t cpuset;
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CPU_ZERO(&cpuset);
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CPU_SET(0, &cpuset);
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if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
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printf("[WARN]\tsched_setaffinity failed\n");
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pthread_t thread;
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if (pthread_create(&thread, 0, threadproc, 0) != 0)
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err(1, "pthread_create");
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#ifdef __x86_64__
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unsigned char *stack32 = mmap(NULL, 4096, PROT_READ | PROT_WRITE,
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MAP_32BIT | MAP_ANONYMOUS | MAP_PRIVATE,
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-1, 0);
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if (stack32 == MAP_FAILED)
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err(1, "mmap");
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#endif
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printf("[RUN]\tSyscalls followed by SS validation\n");
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for (int i = 0; i < 1000; i++) {
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/*
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* Go to sleep and return using sysret (if we're 64-bit
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* or we're 32-bit on AMD on a 64-bit kernel). On AMD CPUs,
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* SYSRET doesn't fix up the cached SS descriptor, so the
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* kernel needs some kind of workaround to make sure that we
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* end the system call with a valid stack segment. This
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* can be a confusing failure because the SS *selector*
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* is the same regardless.
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*/
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usleep(2);
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#ifdef __x86_64__
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/*
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* On 32-bit, just doing a syscall through glibc is enough
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* to cause a crash if our cached SS descriptor is invalid.
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* On 64-bit, it's not, so try extra hard.
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*/
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call32_from_64(stack32 + 4088, test_ss);
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#endif
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}
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printf("[OK]\tWe survived\n");
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#ifdef __x86_64__
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munmap(stack32, 4096);
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#endif
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return 0;
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}
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@ -0,0 +1,67 @@
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/*
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* thunks.S - assembly helpers for mixed-bitness code
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* Copyright (c) 2015 Andrew Lutomirski
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms and conditions of the GNU General Public License,
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* version 2, as published by the Free Software Foundation.
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*
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* This program is distributed in the hope it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* These are little helpers that make it easier to switch bitness on
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* the fly.
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*/
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.text
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.global call32_from_64
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.type call32_from_64, @function
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call32_from_64:
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// rdi: stack to use
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// esi: function to call
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// Save registers
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pushq %rbx
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pushq %rbp
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pushq %r12
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pushq %r13
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pushq %r14
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pushq %r15
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pushfq
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// Switch stacks
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mov %rsp,(%rdi)
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mov %rdi,%rsp
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// Switch to compatibility mode
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pushq $0x23 /* USER32_CS */
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pushq $1f
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lretq
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1:
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.code32
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// Call the function
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call *%esi
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// Switch back to long mode
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jmp $0x33,$1f
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.code64
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1:
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// Restore the stack
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mov (%rsp),%rsp
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// Restore registers
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popfq
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popq %r15
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popq %r14
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popq %r13
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popq %r12
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popq %rbp
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popq %rbx
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ret
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.size call32_from_64, .-call32_from_64
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