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, 40 insertions, 0 deletions

diff --git a/include/crypto/xts.h b/include/crypto/xts.h
new file mode 100644
index 000000000..15b16c485
--- /dev/null
+++ b/include/crypto/xts.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _CRYPTO_XTS_H
+#define _CRYPTO_XTS_H
+
+#include <crypto/b128ops.h>
+#include <crypto/internal/skcipher.h>
+#include <linux/fips.h>
+
+#define XTS_BLOCK_SIZE 16
+
+static inline int xts_verify_key(struct crypto_skcipher *tfm,
+				 const u8 *key, unsigned int keylen)
+{
+	/*
+	 * key consists of keys of equal size concatenated, therefore
+	 * the length must be even.
+	 */
+	if (keylen % 2)
+		return -EINVAL;
+
+	/*
+	 * In FIPS mode only a combined key length of either 256 or
+	 * 512 bits is allowed, c.f. FIPS 140-3 IG C.I.
+	 */
+	if (fips_enabled && keylen != 32 && keylen != 64)
+		return -EINVAL;
+
+	/*
+	 * Ensure that the AES and tweak key are not identical when
+	 * in FIPS mode or the FORBID_WEAK_KEYS flag is set.
+	 */
+	if ((fips_enabled || (crypto_skcipher_get_flags(tfm) &
+			      CRYPTO_TFM_REQ_FORBID_WEAK_KEYS)) &&
+	    !crypto_memneq(key, key + (keylen / 2), keylen / 2))
+		return -EINVAL;
+
+	return 0;
+}
+
+#endif  /* _CRYPTO_XTS_H */