mirror of
git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git
synced 2026-11-09 11:00:49 +01:00
Borislav Petkov
7879fc4bdc
It turned out recently that on certain AMD F15h and F16h machines, due
to the BIOS dropping the ball after resume, yet again, RDRAND would not
function anymore:
c49a0a8013 ("x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h")
Add a silly test to the CPU bringup path, to sanity-check the random
data RDRAND returns and scream as loudly as possible if that returned
random data doesn't change.
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Pu Wen <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/CAHk-=wjWPDauemCmLTKbdMYFB0UveMszZpcrwoUkJRRWKrqaTw@mail.gmail.com
67 lines
1.4 KiB
C
67 lines
1.4 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* This file is part of the Linux kernel.
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*
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* Copyright (c) 2011, Intel Corporation
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* Authors: Fenghua Yu <[email protected]>,
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* H. Peter Anvin <[email protected]>
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*/
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#include <asm/processor.h>
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#include <asm/archrandom.h>
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#include <asm/sections.h>
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static int __init x86_rdrand_setup(char *s)
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{
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setup_clear_cpu_cap(X86_FEATURE_RDRAND);
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setup_clear_cpu_cap(X86_FEATURE_RDSEED);
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return 1;
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}
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__setup("nordrand", x86_rdrand_setup);
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/*
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* RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
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* Run the instruction a few times as a sanity check.
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* If it fails, it is simple to disable RDRAND here.
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*/
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#define SANITY_CHECK_LOOPS 8
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#ifdef CONFIG_ARCH_RANDOM
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void x86_init_rdrand(struct cpuinfo_x86 *c)
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{
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unsigned int changed = 0;
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unsigned long tmp, prev;
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int i;
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if (!cpu_has(c, X86_FEATURE_RDRAND))
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return;
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for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
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if (!rdrand_long(&tmp)) {
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clear_cpu_cap(c, X86_FEATURE_RDRAND);
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pr_warn_once("rdrand: disabled\n");
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return;
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}
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}
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/*
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* Stupid sanity-check whether RDRAND does *actually* generate
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* some at least random-looking data.
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*/
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prev = tmp;
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for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
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if (rdrand_long(&tmp)) {
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if (prev != tmp)
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changed++;
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prev = tmp;
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}
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}
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if (WARN_ON_ONCE(!changed))
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pr_emerg(
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"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
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}
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#endif
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