crypto: jitterentropy - use ktime_get_ns as fallback (b578456c) · Commits · 戴 / test

As part of the Y2038 development, __getnstimeofday is not supposed to be used any more. It is now replaced with ktime_get_ns. The Jitter RNG uses the time stamp to measure the execution time of a given code path and tries to detect variations in the execution time. Therefore, the only requirement the Jitter RNG has, is a sufficient high resolution to detect these variations. The change was tested on x86 to show an identical behavior as RDTSC. The used test code simply measures the execution time of the heart of the RNG: jent_get_nstime(&time); jent_memaccess(ec, min); jent_fold_time(NULL, time, &folded, min); jent_get_nstime(&time2); return ((time2 - time)); Signed-off-by:

Stephan Mueller <smueller@chronox.de> Acked-by:

Arnd Bergmann <arnd@arndb.de> Signed-off-by:

Herbert Xu <herbert@gondor.apana.org.au>

crypto/jitterentropy-kcapi.c

+13 −9

Original line number	Diff line number	Diff line
		@@ -87,24 +87,28 @@ void jent_memcpy(void dest, const void src, unsigned int n)
		memcpy(dest, src, n);
		}

		/*
		* Obtain a high-resolution time stamp value. The time stamp is used to measure
		* the execution time of a given code path and its variations. Hence, the time
		* stamp must have a sufficiently high resolution.
		*
		* Note, if the function returns zero because a given architecture does not
		* implement a high-resolution time stamp, the RNG code's runtime test
		* will detect it and will not produce output.
		*/
		void jent_get_nstime(__u64 *out)
		{
		struct timespec ts;
		__u64 tmp = 0;

		tmp = random_get_entropy();

		/*
		* If random_get_entropy does not return a value (which is possible on,
		* for example, MIPS), invoke __getnstimeofday
		* If random_get_entropy does not return a value, i.e. it is not
		* implemented for a given architecture, use a clock source.
		* hoping that there are timers we can work with.
		*/
		if ((0 == tmp) &&
		(0 == __getnstimeofday(&ts))) {
		tmp = ts.tv_sec;
		tmp = tmp << 32;
		tmp = tmp \| ts.tv_nsec;
		}
		if (tmp == 0)
		tmp = ktime_get_ns();

		*out = tmp;
		}

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