openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 187 insertions, 0 deletions

diff --git a/crypto/cbc.c b/crypto/cbc.c
new file mode 100644
index 000000000..ed3df6246
--- /dev/null
+++ b/crypto/cbc.c
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * CBC: Cipher Block Chaining mode
+ *
+ * Copyright (c) 2006-2016 Herbert Xu <herbert@gondor.apana.org.au>
+ */
+
+#include <crypto/internal/skcipher.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/log2.h>
+#include <linux/module.h>
+
+static int crypto_cbc_encrypt_segment(struct crypto_lskcipher *tfm,
+				      const u8 *src, u8 *dst, unsigned nbytes,
+				      u8 *iv)
+{
+	unsigned int bsize = crypto_lskcipher_blocksize(tfm);
+
+	for (; nbytes >= bsize; src += bsize, dst += bsize, nbytes -= bsize) {
+		crypto_xor(iv, src, bsize);
+		crypto_lskcipher_encrypt(tfm, iv, dst, bsize, NULL);
+		memcpy(iv, dst, bsize);
+	}
+
+	return nbytes;
+}
+
+static int crypto_cbc_encrypt_inplace(struct crypto_lskcipher *tfm,
+				      u8 *src, unsigned nbytes, u8 *oiv)
+{
+	unsigned int bsize = crypto_lskcipher_blocksize(tfm);
+	u8 *iv = oiv;
+
+	if (nbytes < bsize)
+		goto out;
+
+	do {
+		crypto_xor(src, iv, bsize);
+		crypto_lskcipher_encrypt(tfm, src, src, bsize, NULL);
+		iv = src;
+
+		src += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	memcpy(oiv, iv, bsize);
+
+out:
+	return nbytes;
+}
+
+static int crypto_cbc_encrypt(struct crypto_lskcipher *tfm, const u8 *src,
+			      u8 *dst, unsigned len, u8 *iv, u32 flags)
+{
+	struct crypto_lskcipher **ctx = crypto_lskcipher_ctx(tfm);
+	bool final = flags & CRYPTO_LSKCIPHER_FLAG_FINAL;
+	struct crypto_lskcipher *cipher = *ctx;
+	int rem;
+
+	if (src == dst)
+		rem = crypto_cbc_encrypt_inplace(cipher, dst, len, iv);
+	else
+		rem = crypto_cbc_encrypt_segment(cipher, src, dst, len, iv);
+
+	return rem && final ? -EINVAL : rem;
+}
+
+static int crypto_cbc_decrypt_segment(struct crypto_lskcipher *tfm,
+				      const u8 *src, u8 *dst, unsigned nbytes,
+				      u8 *oiv)
+{
+	unsigned int bsize = crypto_lskcipher_blocksize(tfm);
+	const u8 *iv = oiv;
+
+	if (nbytes < bsize)
+		goto out;
+
+	do {
+		crypto_lskcipher_decrypt(tfm, src, dst, bsize, NULL);
+		crypto_xor(dst, iv, bsize);
+		iv = src;
+
+		src += bsize;
+		dst += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	memcpy(oiv, iv, bsize);
+
+out:
+	return nbytes;
+}
+
+static int crypto_cbc_decrypt_inplace(struct crypto_lskcipher *tfm,
+				      u8 *src, unsigned nbytes, u8 *iv)
+{
+	unsigned int bsize = crypto_lskcipher_blocksize(tfm);
+	u8 last_iv[MAX_CIPHER_BLOCKSIZE];
+
+	if (nbytes < bsize)
+		goto out;
+
+	/* Start of the last block. */
+	src += nbytes - (nbytes & (bsize - 1)) - bsize;
+	memcpy(last_iv, src, bsize);
+
+	for (;;) {
+		crypto_lskcipher_decrypt(tfm, src, src, bsize, NULL);
+		if ((nbytes -= bsize) < bsize)
+			break;
+		crypto_xor(src, src - bsize, bsize);
+		src -= bsize;
+	}
+
+	crypto_xor(src, iv, bsize);
+	memcpy(iv, last_iv, bsize);
+
+out:
+	return nbytes;
+}
+
+static int crypto_cbc_decrypt(struct crypto_lskcipher *tfm, const u8 *src,
+			      u8 *dst, unsigned len, u8 *iv, u32 flags)
+{
+	struct crypto_lskcipher **ctx = crypto_lskcipher_ctx(tfm);
+	bool final = flags & CRYPTO_LSKCIPHER_FLAG_FINAL;
+	struct crypto_lskcipher *cipher = *ctx;
+	int rem;
+
+	if (src == dst)
+		rem = crypto_cbc_decrypt_inplace(cipher, dst, len, iv);
+	else
+		rem = crypto_cbc_decrypt_segment(cipher, src, dst, len, iv);
+
+	return rem && final ? -EINVAL : rem;
+}
+
+static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	struct lskcipher_instance *inst;
+	int err;
+
+	inst = lskcipher_alloc_instance_simple(tmpl, tb);
+	if (IS_ERR(inst))
+		return PTR_ERR(inst);
+
+	err = -EINVAL;
+	if (!is_power_of_2(inst->alg.co.base.cra_blocksize))
+		goto out_free_inst;
+
+	if (inst->alg.co.statesize)
+		goto out_free_inst;
+
+	inst->alg.encrypt = crypto_cbc_encrypt;
+	inst->alg.decrypt = crypto_cbc_decrypt;
+
+	err = lskcipher_register_instance(tmpl, inst);
+	if (err) {
+out_free_inst:
+		inst->free(inst);
+	}
+
+	return err;
+}
+
+static struct crypto_template crypto_cbc_tmpl = {
+	.name = "cbc",
+	.create = crypto_cbc_create,
+	.module = THIS_MODULE,
+};
+
+static int __init crypto_cbc_module_init(void)
+{
+	return crypto_register_template(&crypto_cbc_tmpl);
+}
+
+static void __exit crypto_cbc_module_exit(void)
+{
+	crypto_unregister_template(&crypto_cbc_tmpl);
+}
+
+module_init(crypto_cbc_module_init);
+module_exit(crypto_cbc_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("CBC block cipher mode of operation");
+MODULE_ALIAS_CRYPTO("cbc");