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Date:   Fri, 18 Dec 2020 18:01:03 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-crypto@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Dave Martin <dave.martin@....com>,
        Mark Brown <broonie@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Biggers <ebiggers@...nel.org>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: [RFC PATCH 2/5] crypto: skcipher - disallow en/decrypt for non-task or non-softirq context

In order to ensure that kernel mode SIMD routines will not need a scalar
fallback if they run with softirqs disabled, disallow any use of the
skcipher encrypt and decrypt routines from outside of task or softirq
context.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 crypto/skcipher.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/crypto/skcipher.c b/crypto/skcipher.c
index b4dae640de9f..d1a656d7d498 100644
--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -628,6 +628,11 @@ int crypto_skcipher_encrypt(struct skcipher_request *req)
 	unsigned int cryptlen = req->cryptlen;
 	int ret;
 
+	if (!(alg->cra_flags & CRYPTO_ALG_ASYNC) &&
+	    WARN_ONCE(!in_task() && !in_serving_softirq(),
+		      "synchronous call from invalid context\n"))
+		return -EBUSY;
+
 	crypto_stats_get(alg);
 	if (crypto_skcipher_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
 		ret = -ENOKEY;
@@ -645,6 +650,11 @@ int crypto_skcipher_decrypt(struct skcipher_request *req)
 	unsigned int cryptlen = req->cryptlen;
 	int ret;
 
+	if (!(alg->cra_flags & CRYPTO_ALG_ASYNC) &&
+	    WARN_ONCE(!in_task() && !in_serving_softirq(),
+		      "synchronous call from invalid context\n"))
+		return -EBUSY;
+
 	crypto_stats_get(alg);
 	if (crypto_skcipher_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
 		ret = -ENOKEY;
-- 
2.17.1

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