[PATCH] DM: crypto/fsl: fix unaligned exponent handling in fsl_rsa

[Peng Fan]

On Sun, Apr 05, 2026 at 04:54:43PM +0300, Oleksandr Suvorov wrote:
>The RSA verification path loads the public exponent from the FIT key
>node with fdt_getprop(). That property buffer is not guaranteed to be
>naturally aligned. On ARM64 this can lead to a synchronous abort when
>fsl_rsa uses the exponent value directly during verified boot.
>
>Fix the driver by copying the exponent into an aligned local buffer
>before building the CAAM RSA job descriptor. Read the value with the
>pointer-safe fdt64_to_cpu() helper and pass the aligned copy to the
>engine instead of the original FDT property buffer.
>
>Also flush the cache for the aligned exponent buffer actually consumed
>by CAAM so the cache maintenance matches the data path used by the
>hardware.
>
>This keeps RSA verification functional while avoiding crashes caused by
>unaligned FDT property access.
>
>[1]
>---
>
>Trying to boot from MMC2
>    sha256,rsa2048:dev"Synchronous Abort" handler, esr 0x96000021
>    elr: 00000000007e737c lr : 00000000007e6e78
>    x 0: 00000000007fd1e4 x 1: 0000000000000100
>    x 2: 0000000000000800 x 3: 000000000091d420
>    x 4: 000000000091d420 x 5: 000000000091d588
>    x 6: 00000000401ff9b8 x 7: 0000000000000003
>    x 8: 000000000091d49c x 9: 0000000000000002
>...
>    Code: f94008a0 2a0103f4 aa0303f5 b40005c0 (f9400003)
>    Resetting CPU ...
>---
>
>Fixes: 34276478f7b7 ("DM: crypto/fsl - Add Freescale rsa DM driver")
>Signed-off-by: Oleksandr Suvorov <cryosay at gmail.com>
>---
> drivers/crypto/fsl/fsl_rsa.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/crypto/fsl/fsl_rsa.c b/drivers/crypto/fsl/fsl_rsa.c
>index 125a72ae6d3..053e1862bc4 100644
>--- a/drivers/crypto/fsl/fsl_rsa.c
>+++ b/drivers/crypto/fsl/fsl_rsa.c
>@@ -23,6 +23,7 @@ int fsl_mod_exp(struct udevice *dev, const uint8_t *sig, uint32_t sig_len,
> 	struct pk_in_params pkin;
> 	uint32_t desc[MAX_CAAM_DESCSIZE];
> 	int ret;
>+	fdt64_t exp = fdt64_to_cpu(prop->public_exponent);

Build warning->error.

+In file included from include/linux/byteorder/little_endian.h:14,
+                 from arch/arm/include/asm/byteorder.h:28,
+                 from include/linux/libfdt_env.h:15,
+                 from include/linux/libfdt.h:6,
+                 from include/fdtdec.h:17,
+                 from include/dm/ofnode.h:11,
+                 from include/dm/device.h:13,
+                 from include/dm.h:13,
+                 from drivers/crypto/fsl/fsl_rsa.c:9:
+drivers/crypto/fsl/fsl_rsa.c: In function 'fsl_mod_exp':
+include/linux/byteorder/little_endian.h:39:50: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
+   39 | #define __be64_to_cpu(x) __swab64((__force __u64)(__be64)(x))
+      |                                                  ^
+include/linux/byteorder/swab.h:92:31: note: in definition of macro '__swab64'
+   92 | (__builtin_constant_p((__u64)(x)) ? \
+      |                               ^
+include/linux/byteorder/generic.h:93:21: note: in expansion of macro '__be64_to_cpu'
+   93 | #define be64_to_cpu __be64_to_cpu
+      |                     ^~~~~~~~~~~~~
+include/linux/libfdt_env.h:24:25: note: in expansion of macro 'be64_to_cpu'
+   24 | #define fdt64_to_cpu(x) be64_to_cpu(x)
+      |                         ^~~~~~~~~~~
+drivers/crypto/fsl/fsl_rsa.c:26:23: note: in expansion of macro 'fdt64_to_cpu'
+   26 |         fdt64_t exp = fdt64_to_cpu(prop->public_exponent);
+      |                       ^~~~~~~~~~~~
+include/linux/byteorder/swab.h:33:34: note: in definition of macro '___swab64'
+   33 |                 (__u64)(((__u64)(x) & (__u64)0x00000000000000ffULL) << 56) | \
+      |                                  ^
+include/linux/byteorder/little_endian.h:39:26: note: in expansion of macro '__swab64'
+      |                          ^~~~~~~~
+include/linux/byteorder/swab.h:34:34: note: in definition of macro '___swab64'
+   34 |                 (__u64)(((__u64)(x) & (__u64)0x000000000000ff00ULL) << 40) | \
+include/linux/byteorder/swab.h:35:34: note: in definition of macro '___swab64'
+   35 |                 (__u64)(((__u64)(x) & (__u64)0x0000000000ff0000ULL) << 24) | \
+include/linux/byteorder/swab.h:36:34: note: in definition of macro '___swab64'
+   36 |                 (__u64)(((__u64)(x) & (__u64)0x00000000ff000000ULL) <<  8) | \
+include/linux/byteorder/swab.h:37:34: note: in definition of macro '___swab64'
+   37 |                 (__u64)(((__u64)(x) & (__u64)0x000000ff00000000ULL) >>  8) | \
+include/linux/byteorder/swab.h:38:34: note: in definition of macro '___swab64'
+   38 |                 (__u64)(((__u64)(x) & (__u64)0x0000ff0000000000ULL) >> 24) | \
+include/linux/byteorder/swab.h:93:2: note: in expansion of macro '___swab64'
+   93 |  ___swab64((x)) : \
+      |  ^~~~~~~~~
+include/linux/byteorder/swab.h:40:34: note: in definition of macro '___swab64'
+   40 |                 (__u64)(((__u64)(x) & (__u64)0xff00000000000000ULL) >> 56) ))
+include/linux/byteorder/swab.h:94:13: note: in definition of macro '__swab64'
+   94 |  __fswab64((x)))
+      |             ^
+cc1: all warnings being treated as errors
+make[4]: *** [scripts/Makefile.build:271: drivers/crypto/fsl/fsl_rsa.o] Error

Regards
Peng