Re: [PATCH] crypto: crypto4xx - Remove insecure and unused rng_alg

From: Christian Lamparter

Date: Sat May 30 2026 - 06:21:19 EST

Hi!

On 5/30/26 12:04 AM, Eric Biggers wrote:

Remove crypto4xx_rng, as it is insecure and unused:

- It has only a 64-bit security strength, which is highly inadequate.
This can be seen by the fact that crypto4xx_hw_init() seeds it with
only 64 bits of entropy, and the fact that the original commit
mentions that it implements ANSI X9.17 Annex C.

Yes, that "ANSI X9.17 Annex C" comes from the datasheet for the PRNG.

Another issue was that this driver didn't implement the crypto_rng API
correctly, as crypto4xx_prng_generate() didn't return 0 on success.

Oh! Hmm, I think I copied that "return amount;" from another driver that
had it implemented? But I'm not sure, this was sooo long ago. That said,
if this never worked...

- No user of this code is known. It's usable only theoretically via the
"rng" algorithm type of AF_ALG. But userspace actually just uses the
actual Linux RNG (/dev/random etc) instead. And rng_algs don't
contribute entropy to the actual Linux RNG either. (This may have
been confused with hwrng, which does contribute entropy.)

... and it's completely redundant: Sure!

just in case, this counts for anything, but as the person that added it in the
first place:

Acked-by: Christian Lamparter <chunkeey@xxxxxxxxx>

Fixes: d072bfa48853 ("crypto: crypto4xx - add prng crypto support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
drivers/crypto/Kconfig | 1 -
drivers/crypto/amcc/crypto4xx_core.c | 88 -------------------------
drivers/crypto/amcc/crypto4xx_core.h | 4 --
drivers/crypto/amcc/crypto4xx_reg_def.h | 11 ----
4 files changed, 104 deletions(-)

diff --git a/drivers/crypto/Kconfig b/drivers/crypto/Kconfig
index 3449b3c9c6ad..5dab813a9f74 100644
--- a/drivers/crypto/Kconfig
+++ b/drivers/crypto/Kconfig
@@ -299,11 +299,10 @@ config CRYPTO_DEV_PPC4XX
select CRYPTO_AES
select CRYPTO_LIB_AES
select CRYPTO_CCM
select CRYPTO_CTR
select CRYPTO_GCM
- select CRYPTO_RNG
select CRYPTO_SKCIPHER
help
This option allows you to have support for AMCC crypto acceleration.
config HW_RANDOM_PPC4XX
diff --git a/drivers/crypto/amcc/crypto4xx_core.c b/drivers/crypto/amcc/crypto4xx_core.c
index b7b6c97d2147..68c5ff7a85b4 100644
--- a/drivers/crypto/amcc/crypto4xx_core.c
+++ b/drivers/crypto/amcc/crypto4xx_core.c
@@ -29,15 +29,13 @@
#include <crypto/aead.h>
#include <crypto/aes.h>
#include <crypto/ctr.h>
#include <crypto/gcm.h>
#include <crypto/sha1.h>
-#include <crypto/rng.h>
#include <crypto/scatterwalk.h>
#include <crypto/skcipher.h>
#include <crypto/internal/aead.h>
-#include <crypto/internal/rng.h>
#include <crypto/internal/skcipher.h>
#include "crypto4xx_reg_def.h"
#include "crypto4xx_core.h"
#include "crypto4xx_sa.h"
#include "crypto4xx_trng.h"
@@ -983,14 +981,10 @@ static int crypto4xx_register_alg(struct crypto4xx_device *sec_dev,
switch (alg->alg.type) {
case CRYPTO_ALG_TYPE_AEAD:
rc = crypto_register_aead(&alg->alg.u.aead);
break;
- case CRYPTO_ALG_TYPE_RNG:
- rc = crypto_register_rng(&alg->alg.u.rng);
- break;
-
default:
rc = crypto_register_skcipher(&alg->alg.u.cipher);
break;
}
@@ -1012,14 +1006,10 @@ static void crypto4xx_unregister_alg(struct crypto4xx_device *sec_dev)
switch (alg->alg.type) {
case CRYPTO_ALG_TYPE_AEAD:
crypto_unregister_aead(&alg->alg.u.aead);
break;
- case CRYPTO_ALG_TYPE_RNG:
- crypto_unregister_rng(&alg->alg.u.rng);
- break;
-
default:
crypto_unregister_skcipher(&alg->alg.u.cipher);
}
kfree(alg);
}
@@ -1074,73 +1064,10 @@ static irqreturn_t crypto4xx_ce_interrupt_handler_revb(int irq, void *data)
{
return crypto4xx_interrupt_handler(irq, data, PPC4XX_INTERRUPT_CLR |
PPC4XX_TMO_ERR_INT);
}
-static int ppc4xx_prng_data_read(struct crypto4xx_device *dev,
- u8 *data, unsigned int max)
-{
- unsigned int i, curr = 0;
- u32 val[2];
-
- do {
- /* trigger PRN generation */
- writel(PPC4XX_PRNG_CTRL_AUTO_EN,
- dev->ce_base + CRYPTO4XX_PRNG_CTRL);
-
- for (i = 0; i < 1024; i++) {
- /* usually 19 iterations are enough */
- if ((readl(dev->ce_base + CRYPTO4XX_PRNG_STAT) &
- CRYPTO4XX_PRNG_STAT_BUSY))
- continue;
-
- val[0] = readl_be(dev->ce_base + CRYPTO4XX_PRNG_RES_0);
- val[1] = readl_be(dev->ce_base + CRYPTO4XX_PRNG_RES_1);
- break;
- }
- if (i == 1024)
- return -ETIMEDOUT;
-
- if ((max - curr) >= 8) {
- memcpy(data, &val, 8);
- data += 8;
- curr += 8;
- } else {
- /* copy only remaining bytes */
- memcpy(data, &val, max - curr);
- break;
- }
- } while (curr < max);
-
- return curr;
-}
-
-static int crypto4xx_prng_generate(struct crypto_rng *tfm,
- const u8 *src, unsigned int slen,
- u8 *dstn, unsigned int dlen)
-{
- struct rng_alg *alg = crypto_rng_alg(tfm);
- struct crypto4xx_alg *amcc_alg;
- struct crypto4xx_device *dev;
- int ret;
-
- amcc_alg = container_of(alg, struct crypto4xx_alg, alg.u.rng);
- dev = amcc_alg->dev;
-
- mutex_lock(&dev->core_dev->rng_lock);
- ret = ppc4xx_prng_data_read(dev, dstn, dlen);
- mutex_unlock(&dev->core_dev->rng_lock);
- return ret;
-}
-
-
-static int crypto4xx_prng_seed(struct crypto_rng *tfm, const u8 *seed,
- unsigned int slen)
-{
- return 0;
-}
-
/*
* Supported Crypto Algorithms
*/
static struct crypto4xx_alg_common crypto4xx_alg[] = {
/* Crypto AES modes */
@@ -1266,22 +1193,10 @@ static struct crypto4xx_alg_common crypto4xx_alg[] = {
.cra_blocksize = 1,
.cra_ctxsize = sizeof(struct crypto4xx_ctx),
.cra_module = THIS_MODULE,
},
} },
- { .type = CRYPTO_ALG_TYPE_RNG, .u.rng = {
- .base = {
- .cra_name = "stdrng",
- .cra_driver_name = "crypto4xx_rng",
- .cra_priority = 300,
- .cra_ctxsize = 0,
- .cra_module = THIS_MODULE,
- },
- .generate = crypto4xx_prng_generate,
- .seed = crypto4xx_prng_seed,
- .seedsize = 0,
- } },
};
/*
* Module Initialization Routine
*/
@@ -1351,13 +1266,10 @@ static int crypto4xx_probe(struct platform_device *ofdev)
}
core_dev->dev->core_dev = core_dev;
core_dev->dev->is_revb = is_revb;
core_dev->device = dev;
- rc = devm_mutex_init(&ofdev->dev, &core_dev->rng_lock);
- if (rc)
- return rc;
spin_lock_init(&core_dev->lock);
INIT_LIST_HEAD(&core_dev->dev->alg_list);
ratelimit_default_init(&core_dev->dev->aead_ratelimit);
rc = crypto4xx_build_sdr(core_dev->dev);
if (rc)
diff --git a/drivers/crypto/amcc/crypto4xx_core.h b/drivers/crypto/amcc/crypto4xx_core.h
index ee36630c670f..3a028aec3f0c 100644
--- a/drivers/crypto/amcc/crypto4xx_core.h
+++ b/drivers/crypto/amcc/crypto4xx_core.h
@@ -12,14 +12,12 @@
#ifndef __CRYPTO4XX_CORE_H__
#define __CRYPTO4XX_CORE_H__
#include <linux/ratelimit.h>
-#include <linux/mutex.h>
#include <linux/scatterlist.h>
#include <crypto/internal/aead.h>
-#include <crypto/internal/rng.h>
#include <crypto/internal/skcipher.h>
#include "crypto4xx_reg_def.h"
#include "crypto4xx_sa.h"
#define PPC460SX_SDR0_SRST 0x201
@@ -109,11 +107,10 @@ struct crypto4xx_core_device {
struct hwrng *trng;
u32 int_status;
u32 irq;
struct tasklet_struct tasklet;
spinlock_t lock;
- struct mutex rng_lock;
};
struct crypto4xx_ctx {
struct crypto4xx_device *dev;
struct dynamic_sa_ctl *sa_in;
@@ -133,11 +130,10 @@ struct crypto4xx_aead_reqctx {
struct crypto4xx_alg_common {
u32 type;
union {
struct skcipher_alg cipher;
struct aead_alg aead;
- struct rng_alg rng;
} u;
};
struct crypto4xx_alg {
struct list_head entry;
diff --git a/drivers/crypto/amcc/crypto4xx_reg_def.h b/drivers/crypto/amcc/crypto4xx_reg_def.h
index 1038061224da..73d626308a84 100644
--- a/drivers/crypto/amcc/crypto4xx_reg_def.h
+++ b/drivers/crypto/amcc/crypto4xx_reg_def.h
@@ -88,24 +88,13 @@
#define CRYPTO4XX_DMA_CFG 0x000600d4
#define CRYPTO4XX_BYTE_ORDER_CFG 0x000600d8
#define CRYPTO4XX_ENDIAN_CFG 0x000600d8
-#define CRYPTO4XX_PRNG_STAT 0x00070000
-#define CRYPTO4XX_PRNG_STAT_BUSY 0x1
#define CRYPTO4XX_PRNG_CTRL 0x00070004
#define CRYPTO4XX_PRNG_SEED_L 0x00070008
#define CRYPTO4XX_PRNG_SEED_H 0x0007000c
-
-#define CRYPTO4XX_PRNG_RES_0 0x00070020
-#define CRYPTO4XX_PRNG_RES_1 0x00070024
-#define CRYPTO4XX_PRNG_RES_2 0x00070028
-#define CRYPTO4XX_PRNG_RES_3 0x0007002C
-
-#define CRYPTO4XX_PRNG_LFSR_L 0x00070030
-#define CRYPTO4XX_PRNG_LFSR_H 0x00070034
-

Hmm, don't think these defines will hurt anyone? As these are part of the hardware spec.
Or do you forsee a future where AI-Agents will sent patches hallucinating that it "fixed"
the issue which readds it? I have no idea.

/*
* Initialize CRYPTO ENGINE registers, and memory bases.
*/
#define PPC4XX_PDR_POLL 0x3ff
#define PPC4XX_OUTPUT_THRESHOLD 2

Cheers,
Christian