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Implementing memcpy and memset in terms of __builtin_memcpy and
__builtin_memset is problematic.
GCC at -O2 will replace calls to the builtins with calls to memcpy and
memset (but will generate an inline implementation at -Os). Clang will
replace the builtins with these calls regardless of optimization level.
$ llvm-objdump -dr arch/x86/purgatory/string.o | tail
0000000000000339 memcpy:
339: 48 b8 00 00 00 00 00 00 00 00 movabsq $0, %rax
000000000000033b: R_X86_64_64 memcpy
343: ff e0 jmpq *%rax
0000000000000345 memset:
345: 48 b8 00 00 00 00 00 00 00 00 movabsq $0, %rax
0000000000000347: R_X86_64_64 memset
34f: ff e0
Such code results in infinite recursion at runtime. This is observed
when doing kexec.
Instead, reuse an implementation from arch/x86/boot/compressed/string.c.
This requires to implement a stub function for warn(). Also, Clang may
lower memcmp's that compare against 0 to bcmp's, so add a small definition,
too. See also: commit 5f074f3e19 ("lib/string.c: implement a basic bcmp")
Fixes: 8fc5b4d412 ("purgatory: core purgatory functionality")
Reported-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
Debugged-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
Debugged-by: Manoj Gupta <manojgupta@google.com>
Suggested-by: Alistair Delva <adelva@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
Cc: stable@vger.kernel.org
Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056
Link: https://lkml.kernel.org/r/20190807221539.94583-1-ndesaulniers@google.com
77 lines
1.7 KiB
C
77 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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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 <vgoyal@redhat.com>
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*/
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#include <linux/bug.h>
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#include <linux/sha256.h>
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#include <asm/purgatory.h>
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#include "../boot/string.h"
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unsigned long purgatory_backup_dest __section(.kexec-purgatory);
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unsigned long purgatory_backup_src __section(.kexec-purgatory);
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unsigned long purgatory_backup_sz __section(.kexec-purgatory);
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u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE] __section(.kexec-purgatory);
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struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX] __section(.kexec-purgatory);
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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 (purgatory_backup_dest) {
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memcpy((void *)purgatory_backup_dest,
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(void *)purgatory_backup_src, purgatory_backup_sz);
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}
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return 0;
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}
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static int verify_sha256_digest(void)
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{
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struct kexec_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 = purgatory_sha_regions + ARRAY_SIZE(purgatory_sha_regions);
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for (ptr = purgatory_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, purgatory_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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}
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/*
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* Defined in order to reuse memcpy() and memset() from
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* arch/x86/boot/compressed/string.c
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*/
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void warn(const char *msg) {}
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