netdev - [PATCH] prandom: remove next_pseudo

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Message-ID: <20250210133556.66431-1-theil.markus@gmail.com>
Date: Mon, 10 Feb 2025 14:35:56 +0100
From: Markus Theil <theil.markus@...il.com>
To: linux-kernel@...r.kernel.org
Cc: intel-gfx@...ts.freedesktop.org,
	netdev@...r.kernel.org,
	Jason@...c4.com,
	tytso@....edu,
	Markus Theil <theil.markus@...il.com>
Subject: [PATCH] prandom: remove next_pseudo_random32

next_pseudo_random32 implements a LCG with known bad
statistical properties and is only used in two pieces
of testing code. Remove and convert users to the remaining
single PRNG interface in prandom/random32.

This removes another option of using an insecure PRNG.

This is a preliminary patch for further prandom cleanup:
- In another upcoming patch, I'd like to add more warnings,
  that prandom must not be used for cryptographic purposes.
- Replace the LFSR113 generator with Xoshiro256++, which is
  known to have better statistical properties and does not
  need warmup, when seeded properly.

Signed-off-by: Markus Theil <theil.markus@...il.com>
---
 drivers/gpu/drm/i915/selftests/i915_gem.c        | 7 ++++---
 drivers/media/test-drivers/vivid/vivid-vid-cap.c | 4 +++-
 include/linux/prandom.h                          | 6 ------
 3 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/selftests/i915_gem.c b/drivers/gpu/drm/i915/selftests/i915_gem.c
index 0727492576be..14efa6edd9e6 100644
--- a/drivers/gpu/drm/i915/selftests/i915_gem.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem.c
@@ -45,13 +45,15 @@ static void trash_stolen(struct drm_i915_private *i915)
 	struct i915_ggtt *ggtt = to_gt(i915)->ggtt;
 	const u64 slot = ggtt->error_capture.start;
 	const resource_size_t size = resource_size(&i915->dsm.stolen);
+	struct rnd_state prng;
 	unsigned long page;
-	u32 prng = 0x12345678;
 
 	/* XXX: fsck. needs some more thought... */
 	if (!i915_ggtt_has_aperture(ggtt))
 		return;
 
+	prandom_seed_state(&prng, 0x12345678);
+
 	for (page = 0; page < size; page += PAGE_SIZE) {
 		const dma_addr_t dma = i915->dsm.stolen.start + page;
 		u32 __iomem *s;
@@ -64,8 +66,7 @@ static void trash_stolen(struct drm_i915_private *i915)
 
 		s = io_mapping_map_atomic_wc(&ggtt->iomap, slot);
 		for (x = 0; x < PAGE_SIZE / sizeof(u32); x++) {
-			prng = next_pseudo_random32(prng);
-			iowrite32(prng, &s[x]);
+			iowrite32(prandom_u32_state(&prng), &s[x]);
 		}
 		io_mapping_unmap_atomic(s);
 	}
diff --git a/drivers/media/test-drivers/vivid/vivid-vid-cap.c b/drivers/media/test-drivers/vivid/vivid-vid-cap.c
index b166d90177c6..166372d5f927 100644
--- a/drivers/media/test-drivers/vivid/vivid-vid-cap.c
+++ b/drivers/media/test-drivers/vivid/vivid-vid-cap.c
@@ -300,8 +300,10 @@ void vivid_update_quality(struct vivid_dev *dev)
 	 */
 	freq_modulus = (dev->tv_freq - 676 /* (43.25-1) * 16 */) % (6 * 16);
 	if (freq_modulus > 2 * 16) {
+		struct rnd_state prng;
+		prandom_seed_state(&prng, dev->tv_freq ^ 0x55);
 		tpg_s_quality(&dev->tpg, TPG_QUAL_NOISE,
-			next_pseudo_random32(dev->tv_freq ^ 0x55) & 0x3f);
+			prandom_u32_state(&prng) & 0x3f);
 		return;
 	}
 	if (freq_modulus < 12 /*0.75 * 16*/ || freq_modulus > 20 /*1.25 * 16*/)
diff --git a/include/linux/prandom.h b/include/linux/prandom.h
index f2ed5b72b3d6..ff7dcc3fa105 100644
--- a/include/linux/prandom.h
+++ b/include/linux/prandom.h
@@ -47,10 +47,4 @@ static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
 	state->s4 = __seed(i, 128U);
 }
 
-/* Pseudo random number generator from numerical recipes. */
-static inline u32 next_pseudo_random32(u32 seed)
-{
-	return seed * 1664525 + 1013904223;
-}
-
 #endif
-- 
2.47.2