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, 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");