Commit fff6ad38 authored Dec 30, 2024 by Alberto Escolar Piedras Committed by Dan Kalowsky Jan 22, 2025

drivers: entropy: fix native_posix driver for more than 3 byte requests

Fix the native_posix fake entropy driver for more than 3 byte requests,
and specially for native_sim//64 builds.

The host random() provides a number between 0 and 2**31-1 (INT_MAX),
so bit 32 was always 0.
So when filling a buffer with more than 3 bytes we would be filling
each 4th byte with a byte which always had its MSbit as 0.

For LP64 native_sim//64 builds, this was even worse, as the driver had
another bug where we assumed random() returned the whole long filled,
and therefore all 4 upper bytes would be 0.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>
(cherry picked from commit b3407f04)

parent 7d2ac022

drivers/entropy/fake_entropy_native_posix.c

+4 −1

Changes for drivers/entropy/fake_entropy_native_posix.c: 4 added lines, 1 removed line.
Original line number	Diff line number	Diff line
		@@ -42,7 +42,10 @@ static int entropy_native_posix_get_entropy(const struct device *dev,
		*/
		long value = nsi_host_random();

		size_t to_copy = MIN(length, sizeof(long int));
		/* The host random() provides a number between 0 and 2**31-1. Bit 32 is always 0.
		* So let's just use the lower 3 bytes discarding the upper 7 bits
		*/
		size_t to_copy = MIN(length, 3);

		memcpy(buffer, &value, to_copy);
		buffer += to_copy;

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