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, 83 insertions, 0 deletions

diff --git a/crypto/ecdh_helper.c b/crypto/ecdh_helper.c
new file mode 100644
index 000000000..f18f9028f
--- /dev/null
+++ b/crypto/ecdh_helper.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2016, Intel Corporation
+ * Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
+ */
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/err.h>
+#include <linux/string.h>
+#include <crypto/ecdh.h>
+#include <crypto/kpp.h>
+
+#define ECDH_KPP_SECRET_MIN_SIZE (sizeof(struct kpp_secret) + sizeof(short))
+
+static inline u8 *ecdh_pack_data(void *dst, const void *src, size_t sz)
+{
+	memcpy(dst, src, sz);
+	return dst + sz;
+}
+
+static inline const u8 *ecdh_unpack_data(void *dst, const void *src, size_t sz)
+{
+	memcpy(dst, src, sz);
+	return src + sz;
+}
+
+unsigned int crypto_ecdh_key_len(const struct ecdh *params)
+{
+	return ECDH_KPP_SECRET_MIN_SIZE + params->key_size;
+}
+EXPORT_SYMBOL_GPL(crypto_ecdh_key_len);
+
+int crypto_ecdh_encode_key(char *buf, unsigned int len,
+			   const struct ecdh *params)
+{
+	u8 *ptr = buf;
+	struct kpp_secret secret = {
+		.type = CRYPTO_KPP_SECRET_TYPE_ECDH,
+		.len = len
+	};
+
+	if (unlikely(!buf))
+		return -EINVAL;
+
+	if (len != crypto_ecdh_key_len(params))
+		return -EINVAL;
+
+	ptr = ecdh_pack_data(ptr, &secret, sizeof(secret));
+	ptr = ecdh_pack_data(ptr, &params->key_size, sizeof(params->key_size));
+	ecdh_pack_data(ptr, params->key, params->key_size);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(crypto_ecdh_encode_key);
+
+int crypto_ecdh_decode_key(const char *buf, unsigned int len,
+			   struct ecdh *params)
+{
+	const u8 *ptr = buf;
+	struct kpp_secret secret;
+
+	if (unlikely(!buf || len < ECDH_KPP_SECRET_MIN_SIZE))
+		return -EINVAL;
+
+	ptr = ecdh_unpack_data(&secret, ptr, sizeof(secret));
+	if (secret.type != CRYPTO_KPP_SECRET_TYPE_ECDH)
+		return -EINVAL;
+
+	if (unlikely(len < secret.len))
+		return -EINVAL;
+
+	ptr = ecdh_unpack_data(&params->key_size, ptr, sizeof(params->key_size));
+	if (secret.len != crypto_ecdh_key_len(params))
+		return -EINVAL;
+
+	/* Don't allocate memory. Set pointer to data
+	 * within the given buffer
+	 */
+	params->key = (void *)ptr;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(crypto_ecdh_decode_key);