93 lines
2.3 KiB
C
93 lines
2.3 KiB
C
/* Copyright 2017 The Chromium OS Authors. All rights reserved.
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*
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* Tests entropy source.
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*/
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#include "console.h"
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#include "common.h"
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#include "rollback.h"
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#include "test_util.h"
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#include "timer.h"
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#include "util.h"
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#include "watchdog.h"
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static int buckets[256];
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static const int log2_mult = 2;
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/*
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* log2 (multiplied by 2). For non-power of 2, this rounds to the closest
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* half-integer, otherwise the value is exact.
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*/
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uint32_t log2(int32_t val)
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{
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int val1 = 31 - __builtin_clz(val);
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int val2 = 32 - __builtin_clz(val - 1);
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return log2_mult * (val1 + val2)/2;
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}
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void run_test(int argc, char **argv)
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{
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const int loopcount = 512;
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uint8_t buffer[32];
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timestamp_t t0, t1;
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int i, j;
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uint32_t entropy;
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const int totalcount = loopcount * sizeof(buffer);
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const int log2totalcount = log2(totalcount);
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memset(buckets, 0, sizeof(buckets));
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for (i = 0; i < loopcount; i++) {
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t0 = get_time();
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if (!board_get_entropy(buffer, sizeof(buffer))) {
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ccprintf("Cannot get entropy\n");
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test_fail();
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return;
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}
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t1 = get_time();
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if (i == 0)
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ccprintf("Got %zd bytes in %" PRId64 " us\n",
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sizeof(buffer), t1.val - t0.val);
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for (j = 0; j < sizeof(buffer); j++)
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buckets[buffer[j]]++;
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watchdog_reload();
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}
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ccprintf("Total count: %d\n", totalcount);
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ccprintf("Buckets: ");
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entropy = 0;
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for (j = 0; j < 256; j++) {
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/*
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* Shannon entropy (base 2) is sum of -p[j] * log_2(p[j]).
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* p[j] = buckets[j]/totalcount
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* -p[j] * log_2(p[j])
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* = -(buckets[j]/totalcount) * log_2(buckets[j]/totalcount)
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* = buckets[j] * (log_2(totalcount) - log_2(buckets[j]))
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* / totalcount
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* Our log2() function is scaled by log2_mult, and we defer the
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* division by totalcount until we get the total sum, so we need
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* to divide by (log2_mult * totalcount) at the end.
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*/
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entropy += buckets[j] * (log2totalcount - log2(buckets[j]));
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ccprintf("%d;", buckets[j]);
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cflush();
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}
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ccprintf("\n");
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ccprintf("Entropy: %u/1000 bits\n",
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entropy * 1000 / (log2_mult * totalcount));
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/* We want at least 2 bits of entropy (out of a maximum of 8) */
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if ((entropy / (log2_mult * totalcount)) >= 2)
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test_pass();
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else
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test_fail();
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}
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