[PATCH v3] crypto: rsassa-pkcs1 - Align DMA buffer to CRYPTO_DMA_ALIGN

[Changwei Zou <changwei.zou@canonical.com>]

out_buf is used as a DMA buffer for the RSA verification operation.
If out_buf is not aligned to CRYPTO_DMA_ALIGN, cacheline sharing
problems (data corruption) would occur on CPUs with DMA-incoherent caches,
leading to -EKEYREJECTED.

Fix by aligning out_buf to CRYPTO_DMA_ALIGN using PTR_ALIGN(), and
allocating CRYPTO_DMA_ALIGN - 1 extra bytes in the child_req allocation
to accommodate the alignment padding as child_reqsize is a variable.

The intermittent error 'Key was rejected by service' on i.MX8 with CAAM
can be triggered when loading signed kernel modules.

    for i in $(seq 1 100); do
        sudo modprobe xfs 2>&1 && echo "SUCCESS on attempt $i" \
        && sudo rmmod xfs || echo "FAILED on attempt $i"
    done

Fixes: 8552cb04e083 ("crypto: rsassa-pkcs1 - Copy source data for SG list")
Signed-off-by: Changwei Zou <changwei.zou@canonical.com>
---
 crypto/rsassa-pkcs1.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/crypto/rsassa-pkcs1.c b/crypto/rsassa-pkcs1.c
index 94fa5e9600e7..c683f3c61528 100644
--- a/crypto/rsassa-pkcs1.c
+++ b/crypto/rsassa-pkcs1.c
@@ -237,12 +237,13 @@ static int rsassa_pkcs1_verify(struct crypto_sig *tfm,
 		return -EINVAL;
 
 	/* RFC 8017 sec 8.2.2 step 2 - RSA verification */
-	child_req = kmalloc(sizeof(*child_req) + child_reqsize + ctx->key_size,
-			    GFP_KERNEL);
+	child_req = kmalloc(sizeof(*child_req) + child_reqsize +
+			    ctx->key_size + CRYPTO_DMA_ALIGN - 1, GFP_KERNEL);
 	if (!child_req)
 		return -ENOMEM;
 
-	out_buf = (u8 *)(child_req + 1) + child_reqsize;
+	out_buf = PTR_ALIGN((u8 *)(child_req + 1) + child_reqsize,
+			    CRYPTO_DMA_ALIGN);
 	memcpy(out_buf, src, slen);
 
 	crypto_init_wait(&cwait);
-- 
2.43.0