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, 208 insertions, 0 deletions

diff --git a/crypto/xcbc.c b/crypto/xcbc.c
new file mode 100644
index 000000000..6c5f6766f
--- /dev/null
+++ b/crypto/xcbc.c
@@ -0,0 +1,208 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C)2006 USAGI/WIDE Project
+ *
+ * Author:
+ * 	Kazunori Miyazawa <miyazawa@linux-ipv6.org>
+ */
+
+#include <crypto/internal/cipher.h>
+#include <crypto/internal/hash.h>
+#include <crypto/utils.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+static u_int32_t ks[12] = {0x01010101, 0x01010101, 0x01010101, 0x01010101,
+			   0x02020202, 0x02020202, 0x02020202, 0x02020202,
+			   0x03030303, 0x03030303, 0x03030303, 0x03030303};
+
+/*
+ * +------------------------
+ * | <parent tfm>
+ * +------------------------
+ * | xcbc_tfm_ctx
+ * +------------------------
+ * | consts (block size * 2)
+ * +------------------------
+ */
+struct xcbc_tfm_ctx {
+	struct crypto_cipher *child;
+	u8 consts[];
+};
+
+#define XCBC_BLOCKSIZE	16
+
+static int crypto_xcbc_digest_setkey(struct crypto_shash *parent,
+				     const u8 *inkey, unsigned int keylen)
+{
+	struct xcbc_tfm_ctx *ctx = crypto_shash_ctx(parent);
+	u8 *consts = ctx->consts;
+	int err = 0;
+	u8 key1[XCBC_BLOCKSIZE];
+	int bs = sizeof(key1);
+
+	if ((err = crypto_cipher_setkey(ctx->child, inkey, keylen)))
+		return err;
+
+	crypto_cipher_encrypt_one(ctx->child, consts, (u8 *)ks + bs);
+	crypto_cipher_encrypt_one(ctx->child, consts + bs, (u8 *)ks + bs * 2);
+	crypto_cipher_encrypt_one(ctx->child, key1, (u8 *)ks);
+
+	return crypto_cipher_setkey(ctx->child, key1, bs);
+
+}
+
+static int crypto_xcbc_digest_init(struct shash_desc *pdesc)
+{
+	int bs = crypto_shash_blocksize(pdesc->tfm);
+	u8 *prev = shash_desc_ctx(pdesc);
+
+	memset(prev, 0, bs);
+	return 0;
+}
+
+static int crypto_xcbc_digest_update(struct shash_desc *pdesc, const u8 *p,
+				     unsigned int len)
+{
+	struct crypto_shash *parent = pdesc->tfm;
+	struct xcbc_tfm_ctx *tctx = crypto_shash_ctx(parent);
+	struct crypto_cipher *tfm = tctx->child;
+	int bs = crypto_shash_blocksize(parent);
+	u8 *prev = shash_desc_ctx(pdesc);
+
+	do {
+		crypto_xor(prev, p, bs);
+		crypto_cipher_encrypt_one(tfm, prev, prev);
+		p += bs;
+		len -= bs;
+	} while (len >= bs);
+	return len;
+}
+
+static int crypto_xcbc_digest_finup(struct shash_desc *pdesc, const u8 *src,
+				    unsigned int len, u8 *out)
+{
+	struct crypto_shash *parent = pdesc->tfm;
+	struct xcbc_tfm_ctx *tctx = crypto_shash_ctx(parent);
+	struct crypto_cipher *tfm = tctx->child;
+	int bs = crypto_shash_blocksize(parent);
+	u8 *prev = shash_desc_ctx(pdesc);
+	unsigned int offset = 0;
+
+	crypto_xor(prev, src, len);
+	if (len != bs) {
+		prev[len] ^= 0x80;
+		offset += bs;
+	}
+	crypto_xor(prev, &tctx->consts[offset], bs);
+	crypto_cipher_encrypt_one(tfm, out, prev);
+	return 0;
+}
+
+static int xcbc_init_tfm(struct crypto_tfm *tfm)
+{
+	struct crypto_cipher *cipher;
+	struct crypto_instance *inst = (void *)tfm->__crt_alg;
+	struct crypto_cipher_spawn *spawn = crypto_instance_ctx(inst);
+	struct xcbc_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
+
+	cipher = crypto_spawn_cipher(spawn);
+	if (IS_ERR(cipher))
+		return PTR_ERR(cipher);
+
+	ctx->child = cipher;
+
+	return 0;
+};
+
+static void xcbc_exit_tfm(struct crypto_tfm *tfm)
+{
+	struct xcbc_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
+	crypto_free_cipher(ctx->child);
+}
+
+static int xcbc_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	struct shash_instance *inst;
+	struct crypto_cipher_spawn *spawn;
+	struct crypto_alg *alg;
+	u32 mask;
+	int err;
+
+	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SHASH, &mask);
+	if (err)
+		return err;
+
+	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
+	if (!inst)
+		return -ENOMEM;
+	spawn = shash_instance_ctx(inst);
+
+	err = crypto_grab_cipher(spawn, shash_crypto_instance(inst),
+				 crypto_attr_alg_name(tb[1]), 0, mask);
+	if (err)
+		goto err_free_inst;
+	alg = crypto_spawn_cipher_alg(spawn);
+
+	err = -EINVAL;
+	if (alg->cra_blocksize != XCBC_BLOCKSIZE)
+		goto err_free_inst;
+
+	err = crypto_inst_setname(shash_crypto_instance(inst), tmpl->name, alg);
+	if (err)
+		goto err_free_inst;
+
+	inst->alg.base.cra_priority = alg->cra_priority;
+	inst->alg.base.cra_blocksize = alg->cra_blocksize;
+	inst->alg.base.cra_ctxsize = sizeof(struct xcbc_tfm_ctx) +
+				     alg->cra_blocksize * 2;
+	inst->alg.base.cra_flags = CRYPTO_AHASH_ALG_BLOCK_ONLY |
+				   CRYPTO_AHASH_ALG_FINAL_NONZERO;
+
+	inst->alg.digestsize = alg->cra_blocksize;
+	inst->alg.descsize = alg->cra_blocksize;
+
+	inst->alg.base.cra_init = xcbc_init_tfm;
+	inst->alg.base.cra_exit = xcbc_exit_tfm;
+
+	inst->alg.init = crypto_xcbc_digest_init;
+	inst->alg.update = crypto_xcbc_digest_update;
+	inst->alg.finup = crypto_xcbc_digest_finup;
+	inst->alg.setkey = crypto_xcbc_digest_setkey;
+
+	inst->free = shash_free_singlespawn_instance;
+
+	err = shash_register_instance(tmpl, inst);
+	if (err) {
+err_free_inst:
+		shash_free_singlespawn_instance(inst);
+	}
+	return err;
+}
+
+static struct crypto_template crypto_xcbc_tmpl = {
+	.name = "xcbc",
+	.create = xcbc_create,
+	.module = THIS_MODULE,
+};
+
+static int __init crypto_xcbc_module_init(void)
+{
+	return crypto_register_template(&crypto_xcbc_tmpl);
+}
+
+static void __exit crypto_xcbc_module_exit(void)
+{
+	crypto_unregister_template(&crypto_xcbc_tmpl);
+}
+
+module_init(crypto_xcbc_module_init);
+module_exit(crypto_xcbc_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("XCBC keyed hash algorithm");
+MODULE_ALIAS_CRYPTO("xcbc");
+MODULE_IMPORT_NS("CRYPTO_INTERNAL");