crypto: simd,testmgr - introduce crypto_simd_usable()

So that the no-SIMD fallback code can be tested by the crypto
self-tests, add a macro crypto_simd_usable() which wraps may_use_simd(),
but also returns false if the crypto self-tests have set a per-CPU bool
to disable SIMD in crypto code on the current CPU.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/testmgr.c

@@ -37,6 +37,7 @@
 #include <crypto/akcipher.h>
 #include <crypto/kpp.h>
 #include <crypto/acompress.h>
+#include <crypto/internal/simd.h>
 
 #include "internal.h"
 
@@ -52,6 +53,9 @@ MODULE_PARM_DESC(noextratests, "disable expensive crypto self-tests");
 static unsigned int fuzz_iterations = 100;
 module_param(fuzz_iterations, uint, 0644);
 MODULE_PARM_DESC(fuzz_iterations, "number of fuzz test iterations");
+
+DEFINE_PER_CPU(bool, crypto_simd_disabled_for_test);
+EXPORT_PER_CPU_SYMBOL_GPL(crypto_simd_disabled_for_test);
 #endif
 
 #ifdef CONFIG_CRYPTO_MANAGER_DISABLE_TESTS
@@ -838,7 +842,27 @@ static void generate_random_testvec_config(struct testvec_config *cfg,
 
 	WARN_ON_ONCE(!valid_testvec_config(cfg));
 }
-#endif /* CONFIG_CRYPTO_MANAGER_EXTRA_TESTS */
+
+static void crypto_disable_simd_for_test(void)
+{
+	preempt_disable();
+	__this_cpu_write(crypto_simd_disabled_for_test, true);
+}
+
+static void crypto_reenable_simd_for_test(void)
+{
+	__this_cpu_write(crypto_simd_disabled_for_test, false);
+	preempt_enable();
+}
+#else /* !CONFIG_CRYPTO_MANAGER_EXTRA_TESTS */
+static void crypto_disable_simd_for_test(void)
+{
+}
+
+static void crypto_reenable_simd_for_test(void)
+{
+}
+#endif /* !CONFIG_CRYPTO_MANAGER_EXTRA_TESTS */
 
 static int check_nonfinal_hash_op(const char *op, int err,
 				  u8 *result, unsigned int digestsize,

include/crypto/internal/simd.h

@@ -6,6 +6,9 @@
 #ifndef _CRYPTO_INTERNAL_SIMD_H
 #define _CRYPTO_INTERNAL_SIMD_H
 
+#include <linux/percpu.h>
+#include <linux/types.h>
+
 /* skcipher support */
 
 struct simd_skcipher_alg;
@@ -42,4 +45,25 @@ int simd_register_aeads_compat(struct aead_alg *algs, int count,
 void simd_unregister_aeads(struct aead_alg *algs, int count,
 			   struct simd_aead_alg **simd_algs);
 
+/*
+ * crypto_simd_usable() - is it allowed at this time to use SIMD instructions or
+ *			  access the SIMD register file?
+ *
+ * This delegates to may_use_simd(), except that this also returns false if SIMD
+ * in crypto code has been temporarily disabled on this CPU by the crypto
+ * self-tests, in order to test the no-SIMD fallback code.  This override is
+ * currently limited to configurations where the extra self-tests are enabled,
+ * because it might be a bit too invasive to be part of the regular self-tests.
+ *
+ * This is a macro so that <asm/simd.h>, which some architectures don't have,
+ * doesn't have to be included directly here.
+ */
+#ifdef CONFIG_CRYPTO_MANAGER_EXTRA_TESTS
+DECLARE_PER_CPU(bool, crypto_simd_disabled_for_test);
+#define crypto_simd_usable() \
+	(may_use_simd() && !this_cpu_read(crypto_simd_disabled_for_test))
+#else
+#define crypto_simd_usable() may_use_simd()
+#endif
+
 #endif /* _CRYPTO_INTERNAL_SIMD_H */