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, 82 insertions, 0 deletions

diff --git a/crypto/arc4.c b/crypto/arc4.c
new file mode 100644
index 000000000..160801811
--- /dev/null
+++ b/crypto/arc4.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Cryptographic API
+ *
+ * ARC4 Cipher Algorithm
+ *
+ * Jon Oberheide <jon@oberheide.org>
+ */
+
+#include <crypto/arc4.h>
+#include <crypto/internal/skcipher.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+
+#define ARC4_ALIGN __alignof__(struct arc4_ctx)
+
+static int crypto_arc4_setkey(struct crypto_lskcipher *tfm, const u8 *in_key,
+			      unsigned int key_len)
+{
+	struct arc4_ctx *ctx = crypto_lskcipher_ctx(tfm);
+
+	return arc4_setkey(ctx, in_key, key_len);
+}
+
+static int crypto_arc4_crypt(struct crypto_lskcipher *tfm, const u8 *src,
+			     u8 *dst, unsigned nbytes, u8 *siv, u32 flags)
+{
+	struct arc4_ctx *ctx = crypto_lskcipher_ctx(tfm);
+
+	if (!(flags & CRYPTO_LSKCIPHER_FLAG_CONT))
+		memcpy(siv, ctx, sizeof(*ctx));
+
+	ctx = (struct arc4_ctx *)siv;
+
+	arc4_crypt(ctx, dst, src, nbytes);
+	return 0;
+}
+
+static int crypto_arc4_init(struct crypto_lskcipher *tfm)
+{
+	pr_warn_ratelimited("\"%s\" (%ld) uses obsolete ecb(arc4) skcipher\n",
+			    current->comm, (unsigned long)current->pid);
+
+	return 0;
+}
+
+static struct lskcipher_alg arc4_alg = {
+	.co.base.cra_name		=	"arc4",
+	.co.base.cra_driver_name	=	"arc4-generic",
+	.co.base.cra_priority		=	100,
+	.co.base.cra_blocksize		=	ARC4_BLOCK_SIZE,
+	.co.base.cra_ctxsize		=	sizeof(struct arc4_ctx),
+	.co.base.cra_alignmask		=	ARC4_ALIGN - 1,
+	.co.base.cra_module		=	THIS_MODULE,
+	.co.min_keysize			=	ARC4_MIN_KEY_SIZE,
+	.co.max_keysize			=	ARC4_MAX_KEY_SIZE,
+	.co.statesize			=	sizeof(struct arc4_ctx),
+	.setkey				=	crypto_arc4_setkey,
+	.encrypt			=	crypto_arc4_crypt,
+	.decrypt			=	crypto_arc4_crypt,
+	.init				=	crypto_arc4_init,
+};
+
+static int __init arc4_init(void)
+{
+	return crypto_register_lskcipher(&arc4_alg);
+}
+
+static void __exit arc4_exit(void)
+{
+	crypto_unregister_lskcipher(&arc4_alg);
+}
+
+module_init(arc4_init);
+module_exit(arc4_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
+MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");
+MODULE_ALIAS_CRYPTO("ecb(arc4)");