71 lines
1.7 KiB
Diff
71 lines
1.7 KiB
Diff
From 4d36b0287d3ab0912ba8a4790340ca099960b2b0 Mon Sep 17 00:00:00 2001
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From: Tudor Brindus <me@tbrindus.ca>
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Date: Fri, 1 May 2020 21:09:22 -0400
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Subject: [PATCH] Detect broken RDRAND during initialization
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Some CPUs advertise RDRAND in CPUID, but return 0xFFFFFFFF
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unconditionally. To avoid locking up later, test RDRAND during
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initialization, and if it returns 0xFFFFFFFF, mark it as nonexistent.
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Fixes #588.
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Conflict:NA
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Reference:https://github.com/json-c/json-c/commit/4d36b0287d3ab0912ba8a4790340ca099960b2b0
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---
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random_seed.c | 37 +++++++++++++++++++++++++++++++++----
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1 file changed, 33 insertions(+), 4 deletions(-)
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diff --git a/random_seed.c b/random_seed.c
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index 97d9547..b97dbd1 100644
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--- a/random_seed.c
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+++ b/random_seed.c
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@@ -53,12 +53,41 @@ static void do_cpuid(int regs[], int h)
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#if HAS_X86_CPUID
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+static int get_rdrand_seed(void);
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+
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+// Valid values are -1 (haven't tested), 0 (no), and 1 (yes).
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+static int _has_rdrand = -1;
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+
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static int has_rdrand(void)
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{
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- // CPUID.01H:ECX.RDRAND[bit 30] == 1
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- int regs[4];
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- do_cpuid(regs, 1);
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- return (regs[2] & (1 << 30)) != 0;
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+ if (_has_rdrand == -1)
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+ {
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+ // CPUID.01H:ECX.RDRAND[bit 30] == 1
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+ int regs[4];
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+ do_cpuid(regs, 1);
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+ if (!(regs[2] & (1 << 30)))
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+ {
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+ _has_rdrand = 0;
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+ } else
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+ {
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+ // Some CPUs advertise RDRAND in CPUID, but return 0xFFFFFFFF
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+ // unconditionally. To avoid locking up later, test RDRAND here. If over
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+ // 10 trials RDRAND has returned the same value, declare it broken.
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+ _has_rdrand = 0;
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+ int prev = get_rdrand_seed();
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+ for (int i = 0; i < 10; i++) {
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+ int temp = get_rdrand_seed();
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+ if (temp != prev) {
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+ _has_rdrand = 1;
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+ break;
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+ }
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+
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+ prev = temp;
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+ }
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+ }
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+ }
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+
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+ return _has_rdrand;
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}
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#endif
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--
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2.27.0
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