ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 124 insertions, 0 deletions

diff --git a/crypto/crypto_null.c b/crypto/crypto_null.c
new file mode 100644
index 000000000..fea151df1
--- /dev/null
+++ b/crypto/crypto_null.c
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Cryptographic API.
+ *
+ * Null algorithms, aka Much Ado About Nothing.
+ *
+ * These are needed for IPsec, and may be useful in general for
+ * testing & debugging.
+ *
+ * The null cipher is compliant with RFC2410.
+ *
+ * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
+ */
+
+#include <crypto/null.h>
+#include <crypto/internal/hash.h>
+#include <crypto/internal/skcipher.h>
+#include <crypto/scatterwalk.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/string.h>
+
+static int null_init(struct shash_desc *desc)
+{
+	return 0;
+}
+
+static int null_update(struct shash_desc *desc, const u8 *data,
+		       unsigned int len)
+{
+	return 0;
+}
+
+static int null_final(struct shash_desc *desc, u8 *out)
+{
+	return 0;
+}
+
+static int null_digest(struct shash_desc *desc, const u8 *data,
+		       unsigned int len, u8 *out)
+{
+	return 0;
+}
+
+static int null_hash_setkey(struct crypto_shash *tfm, const u8 *key,
+			    unsigned int keylen)
+{ return 0; }
+
+static int null_skcipher_setkey(struct crypto_skcipher *tfm, const u8 *key,
+				unsigned int keylen)
+{ return 0; }
+
+static int null_skcipher_crypt(struct skcipher_request *req)
+{
+	if (req->src != req->dst)
+		memcpy_sglist(req->dst, req->src, req->cryptlen);
+	return 0;
+}
+
+static struct shash_alg digest_null = {
+	.digestsize		=	NULL_DIGEST_SIZE,
+	.setkey   		=	null_hash_setkey,
+	.init   		=	null_init,
+	.update 		=	null_update,
+	.finup 			=	null_digest,
+	.digest 		=	null_digest,
+	.final  		=	null_final,
+	.base			=	{
+		.cra_name		=	"digest_null",
+		.cra_driver_name	=	"digest_null-generic",
+		.cra_blocksize		=	NULL_BLOCK_SIZE,
+		.cra_module		=	THIS_MODULE,
+	}
+};
+
+static struct skcipher_alg skcipher_null = {
+	.base.cra_name		=	"ecb(cipher_null)",
+	.base.cra_driver_name	=	"ecb-cipher_null",
+	.base.cra_priority	=	100,
+	.base.cra_blocksize	=	NULL_BLOCK_SIZE,
+	.base.cra_ctxsize	=	0,
+	.base.cra_module	=	THIS_MODULE,
+	.min_keysize		=	NULL_KEY_SIZE,
+	.max_keysize		=	NULL_KEY_SIZE,
+	.ivsize			=	NULL_IV_SIZE,
+	.setkey			=	null_skcipher_setkey,
+	.encrypt		=	null_skcipher_crypt,
+	.decrypt		=	null_skcipher_crypt,
+};
+
+MODULE_ALIAS_CRYPTO("digest_null");
+MODULE_ALIAS_CRYPTO("ecb(cipher_null)");
+
+static int __init crypto_null_mod_init(void)
+{
+	int ret = 0;
+
+	ret = crypto_register_shash(&digest_null);
+	if (ret < 0)
+		goto out;
+
+	ret = crypto_register_skcipher(&skcipher_null);
+	if (ret < 0)
+		goto out_unregister_shash;
+
+	return 0;
+
+out_unregister_shash:
+	crypto_unregister_shash(&digest_null);
+out:
+	return ret;
+}
+
+static void __exit crypto_null_mod_fini(void)
+{
+	crypto_unregister_shash(&digest_null);
+	crypto_unregister_skcipher(&skcipher_null);
+}
+
+module_init(crypto_null_mod_init);
+module_exit(crypto_null_mod_fini);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Null Cryptographic Algorithms");