[PATCH] prandom: remove next_pseudo_random32

[PATCH] prandom: remove next_pseudo_random32

[Markus Theil]

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@gmail.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

Re: [PATCH] prandom: remove next_pseudo_random32

[Jason A. Donenfeld]

Hey Markus,

Thanks for this. I hadn't realized that next_pseudo_random32() only
had two users left. Excellent.

I'll queue this up in the random tree (unless there are objections
from the maintainers of that test code).

Jason

Re: [PATCH] prandom: remove next_pseudo_random32

[Andi Shyti]

Hi,

On Mon, Feb 10, 2025 at 02:39:43PM +0100, Jason A. Donenfeld wrote:
> Hey Markus,
> 
> Thanks for this. I hadn't realized that next_pseudo_random32() only
> had two users left. Excellent.
> 
> I'll queue this up in the random tree (unless there are objections
> from the maintainers of that test code).

actually would be better if we apply the i915 part in drm-tip
rather than waiting for kernel releases to receive this change in
our branch. It has been source of conflicts and headaches.

May I ask Markus to split the patch in two parts and we handle
the i915 side?

Thanks,
Andi

Re: [PATCH] prandom: remove next_pseudo_random32

[Markus Theil]

Hi,

On 11.02.25 00:07, Andi Shyti wrote:

> actually would be better if we apply the i915 part in drm-tip
> rather than waiting for kernel releases to receive this change in
> our branch. It has been source of conflicts and headaches.
> 
> May I ask Markus to split the patch in two parts and we handle
> the i915 side?
> 

Sure, will do in a v2.

Markus

[PATCH v2 0/3] prandom: remove next_pseudo_random32

[Markus Theil]

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

This removes another option of using an insecure PRNG.

Markus Theil (3):
  drm/i915/selftests: use prandom in selftest
  media: vivid: use prandom
  prandom: remove next_pseudo_random32

 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(-)

-- 
2.47.2

[PATCH v2 1/3] drm/i915/selftests: use prandom in selftest

[Markus Theil]

This is part of a prandom cleanup, which removes
next_pseudo_random32 and replaces it with the standard PRNG.

Signed-off-by: Markus Theil <theil.markus@gmail.com>
---
 drivers/gpu/drm/i915/selftests/i915_gem.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 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);
 	}
-- 
2.47.2

[PATCH v2 2/3] media: vivid: use prandom

[Markus Theil]

This is part of a prandom cleanup, which removes
next_pseudo_random32 and replaces it with the standard PRNG.

Signed-off-by: Markus Theil <theil.markus@gmail.com>
---
 drivers/media/test-drivers/vivid/vivid-vid-cap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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*/)
-- 
2.47.2

[PATCH v2 3/3] prandom: remove next_pseudo_random32

[Markus Theil]

next_pseudo_random32 implements a LCG with known bad statistical
properties and was only used in two pieces of testing code.

After the users are converted to prandom as part of this series,
remove the LCG here.

This removes another option of using an insecure PRNG.

Signed-off-by: Markus Theil <theil.markus@gmail.com>
---
 include/linux/prandom.h | 6 ------
 1 file changed, 6 deletions(-)

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

Re: [PATCH v2 0/3] prandom: remove next_pseudo_random32

[Krzysztof Karas]

Hi Markus,

> next_pseudo_random32 implements a LCG with known bad statistical
> properties and is only used in two pieces of testing code. Remove and
> convert the remaining two users to the single PRNG interface in
> prandom.h
> 
> This removes another option of using an insecure PRNG.
> 
> Markus Theil (3):
>   drm/i915/selftests: use prandom in selftest
>   media: vivid: use prandom
>   prandom: remove next_pseudo_random32
> 
>  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(-)
>

The series looks good:
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
on all the patches.

Best Regards,
Krzysztof

Re: [PATCH v2 1/3] drm/i915/selftests: use prandom in selftest

[Andi Shyti]

Hi Markus,

On Tue, Feb 11, 2025 at 07:33:30AM +0100, Markus Theil wrote:
> This is part of a prandom cleanup, which removes
> next_pseudo_random32 and replaces it with the standard PRNG.
> 
> Signed-off-by: Markus Theil <theil.markus@gmail.com>

I merged just this patch in drm-intel-gt-next.

Thanks,
Andi

Re: [PATCH v2 1/3] drm/i915/selftests: use prandom in selftest

[Jason A. Donenfeld]

Hi Andi,

On Thu, Feb 13, 2025 at 06:19:12PM +0100, Andi Shyti wrote:
> Hi Markus,
> 
> On Tue, Feb 11, 2025 at 07:33:30AM +0100, Markus Theil wrote:
> > This is part of a prandom cleanup, which removes
> > next_pseudo_random32 and replaces it with the standard PRNG.
> > 
> > Signed-off-by: Markus Theil <theil.markus@gmail.com>
> 
> I merged just this patch in drm-intel-gt-next.

This is minorly annoying for me... What am I supposed to do with patches
2 and 3? Take them through my tree for 6.16 in like half a year? Can I
just take the v1 into my tree and we can get this done with straight
forwardly? Or do you have a different suggestion for me?

Jason

Re: [PATCH v2 1/3] drm/i915/selftests: use prandom in selftest

[Jani Nikula]

On Wed, 19 Mar 2025, "Jason A. Donenfeld" <Jason@zx2c4.com> wrote:
> Hi Andi,
>
> On Thu, Feb 13, 2025 at 06:19:12PM +0100, Andi Shyti wrote:
>> Hi Markus,
>> 
>> On Tue, Feb 11, 2025 at 07:33:30AM +0100, Markus Theil wrote:
>> > This is part of a prandom cleanup, which removes
>> > next_pseudo_random32 and replaces it with the standard PRNG.
>> > 
>> > Signed-off-by: Markus Theil <theil.markus@gmail.com>
>> 
>> I merged just this patch in drm-intel-gt-next.
>
> This is minorly annoying for me... What am I supposed to do with patches
> 2 and 3? Take them through my tree for 6.16 in like half a year? Can I
> just take the v1 into my tree and we can get this done with straight
> forwardly? Or do you have a different suggestion for me?

Feel free to apply it to your tree too. It's not ideal to have two
commits for the same thing, but oh well.

Acked-by: Jani Nikula <jani.nikula@intel.com>

-- 
Jani Nikula, Intel

Re: [PATCH v2 1/3] drm/i915/selftests: use prandom in selftest

[Jason A. Donenfeld]

On Fri, Mar 21, 2025 at 02:37:15PM +0200, Jani Nikula wrote:
> On Wed, 19 Mar 2025, "Jason A. Donenfeld" <Jason@zx2c4.com> wrote:
> > Hi Andi,
> >
> > On Thu, Feb 13, 2025 at 06:19:12PM +0100, Andi Shyti wrote:
> >> Hi Markus,
> >> 
> >> On Tue, Feb 11, 2025 at 07:33:30AM +0100, Markus Theil wrote:
> >> > This is part of a prandom cleanup, which removes
> >> > next_pseudo_random32 and replaces it with the standard PRNG.
> >> > 
> >> > Signed-off-by: Markus Theil <theil.markus@gmail.com>
> >> 
> >> I merged just this patch in drm-intel-gt-next.
> >
> > This is minorly annoying for me... What am I supposed to do with patches
> > 2 and 3? Take them through my tree for 6.16 in like half a year? Can I
> > just take the v1 into my tree and we can get this done with straight
> > forwardly? Or do you have a different suggestion for me?
> 
> Feel free to apply it to your tree too. It's not ideal to have two
> commits for the same thing, but oh well.
> 
> Acked-by: Jani Nikula <jani.nikula@intel.com>

Oh that's a good idea. Thanks!

Jason