sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 127 insertions, 0 deletions

diff --git a/include/crypto/internal/des.h b/include/crypto/internal/des.h
new file mode 100644
index 000000000..723fe5bf1
--- /dev/null
+++ b/include/crypto/internal/des.h
@@ -0,0 +1,127 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DES & Triple DES EDE key verification helpers
+ */
+
+#ifndef __CRYPTO_INTERNAL_DES_H
+#define __CRYPTO_INTERNAL_DES_H
+
+#include <linux/crypto.h>
+#include <linux/fips.h>
+#include <crypto/des.h>
+#include <crypto/aead.h>
+#include <crypto/skcipher.h>
+
+/**
+ * crypto_des_verify_key - Check whether a DES key is weak
+ * @tfm: the crypto algo
+ * @key: the key buffer
+ *
+ * Returns -EINVAL if the key is weak and the crypto TFM does not permit weak
+ * keys. Otherwise, 0 is returned.
+ *
+ * It is the job of the caller to ensure that the size of the key equals
+ * DES_KEY_SIZE.
+ */
+static inline int crypto_des_verify_key(struct crypto_tfm *tfm, const u8 *key)
+{
+	struct des_ctx tmp;
+	int err;
+
+	err = des_expand_key(&tmp, key, DES_KEY_SIZE);
+	if (err == -ENOKEY) {
+		if (crypto_tfm_get_flags(tfm) & CRYPTO_TFM_REQ_FORBID_WEAK_KEYS)
+			err = -EINVAL;
+		else
+			err = 0;
+	}
+	memzero_explicit(&tmp, sizeof(tmp));
+	return err;
+}
+
+/*
+ * RFC2451:
+ *
+ *   For DES-EDE3, there is no known need to reject weak or
+ *   complementation keys.  Any weakness is obviated by the use of
+ *   multiple keys.
+ *
+ *   However, if the first two or last two independent 64-bit keys are
+ *   equal (k1 == k2 or k2 == k3), then the DES3 operation is simply the
+ *   same as DES.  Implementers MUST reject keys that exhibit this
+ *   property.
+ *
+ */
+static inline int des3_ede_verify_key(const u8 *key, unsigned int key_len,
+				      bool check_weak)
+{
+	int ret = fips_enabled ? -EINVAL : -ENOKEY;
+	u32 K[6];
+
+	memcpy(K, key, DES3_EDE_KEY_SIZE);
+
+	if ((!((K[0] ^ K[2]) | (K[1] ^ K[3])) ||
+	     !((K[2] ^ K[4]) | (K[3] ^ K[5]))) &&
+	    (fips_enabled || check_weak))
+		goto bad;
+
+	if ((!((K[0] ^ K[4]) | (K[1] ^ K[5]))) && fips_enabled)
+		goto bad;
+
+	ret = 0;
+bad:
+	memzero_explicit(K, DES3_EDE_KEY_SIZE);
+
+	return ret;
+}
+
+/**
+ * crypto_des3_ede_verify_key - Check whether a DES3-EDE key is weak
+ * @tfm: the crypto algo
+ * @key: the key buffer
+ *
+ * Returns -EINVAL if the key is weak and the crypto TFM does not permit weak
+ * keys or when running in FIPS mode. Otherwise, 0 is returned. Note that some
+ * keys are rejected in FIPS mode even if weak keys are permitted by the TFM
+ * flags.
+ *
+ * It is the job of the caller to ensure that the size of the key equals
+ * DES3_EDE_KEY_SIZE.
+ */
+static inline int crypto_des3_ede_verify_key(struct crypto_tfm *tfm,
+					     const u8 *key)
+{
+	return des3_ede_verify_key(key, DES3_EDE_KEY_SIZE,
+				   crypto_tfm_get_flags(tfm) &
+				   CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
+}
+
+static inline int verify_skcipher_des_key(struct crypto_skcipher *tfm,
+					  const u8 *key)
+{
+	return crypto_des_verify_key(crypto_skcipher_tfm(tfm), key);
+}
+
+static inline int verify_skcipher_des3_key(struct crypto_skcipher *tfm,
+					   const u8 *key)
+{
+	return crypto_des3_ede_verify_key(crypto_skcipher_tfm(tfm), key);
+}
+
+static inline int verify_aead_des_key(struct crypto_aead *tfm, const u8 *key,
+				      int keylen)
+{
+	if (keylen != DES_KEY_SIZE)
+		return -EINVAL;
+	return crypto_des_verify_key(crypto_aead_tfm(tfm), key);
+}
+
+static inline int verify_aead_des3_key(struct crypto_aead *tfm, const u8 *key,
+				       int keylen)
+{
+	if (keylen != DES3_EDE_KEY_SIZE)
+		return -EINVAL;
+	return crypto_des3_ede_verify_key(crypto_aead_tfm(tfm), key);
+}
+
+#endif /* __CRYPTO_INTERNAL_DES_H */