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, 234 insertions, 0 deletions

diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
new file mode 100644
index 000000000..4569045e7
--- /dev/null
+++ b/include/asm-generic/uaccess.h
@@ -0,0 +1,234 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_UACCESS_H
+#define __ASM_GENERIC_UACCESS_H
+
+/*
+ * User space memory access functions, these should work
+ * on any machine that has kernel and user data in the same
+ * address space, e.g. all NOMMU machines.
+ */
+#include <linux/string.h>
+#include <asm-generic/access_ok.h>
+
+#ifdef CONFIG_UACCESS_MEMCPY
+#include <linux/unaligned.h>
+
+static __always_inline int
+__get_user_fn(size_t size, const void __user *from, void *to)
+{
+	BUILD_BUG_ON(!__builtin_constant_p(size));
+
+	switch (size) {
+	case 1:
+		*(u8 *)to = *((u8 __force *)from);
+		return 0;
+	case 2:
+		*(u16 *)to = get_unaligned((u16 __force *)from);
+		return 0;
+	case 4:
+		*(u32 *)to = get_unaligned((u32 __force *)from);
+		return 0;
+	case 8:
+		*(u64 *)to = get_unaligned((u64 __force *)from);
+		return 0;
+	default:
+		BUILD_BUG();
+		return 0;
+	}
+
+}
+#define __get_user_fn(sz, u, k)	__get_user_fn(sz, u, k)
+
+static __always_inline int
+__put_user_fn(size_t size, void __user *to, void *from)
+{
+	BUILD_BUG_ON(!__builtin_constant_p(size));
+
+	switch (size) {
+	case 1:
+		*(u8 __force *)to = *(u8 *)from;
+		return 0;
+	case 2:
+		put_unaligned(*(u16 *)from, (u16 __force *)to);
+		return 0;
+	case 4:
+		put_unaligned(*(u32 *)from, (u32 __force *)to);
+		return 0;
+	case 8:
+		put_unaligned(*(u64 *)from, (u64 __force *)to);
+		return 0;
+	default:
+		BUILD_BUG();
+		return 0;
+	}
+}
+#define __put_user_fn(sz, u, k)	__put_user_fn(sz, u, k)
+
+#define __get_kernel_nofault(dst, src, type, err_label)			\
+do {									\
+	*((type *)dst) = get_unaligned((type *)(src));			\
+	if (0) /* make sure the label looks used to the compiler */	\
+		goto err_label;						\
+} while (0)
+
+#define __put_kernel_nofault(dst, src, type, err_label)			\
+do {									\
+	put_unaligned(*((type *)src), (type *)(dst));			\
+	if (0) /* make sure the label looks used to the compiler */	\
+		goto err_label;						\
+} while (0)
+
+static inline __must_check unsigned long
+raw_copy_from_user(void *to, const void __user * from, unsigned long n)
+{
+	memcpy(to, (const void __force *)from, n);
+	return 0;
+}
+
+static inline __must_check unsigned long
+raw_copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+	memcpy((void __force *)to, from, n);
+	return 0;
+}
+#define INLINE_COPY_USER
+#endif /* CONFIG_UACCESS_MEMCPY */
+
+/*
+ * These are the main single-value transfer routines.  They automatically
+ * use the right size if we just have the right pointer type.
+ * This version just falls back to copy_{from,to}_user, which should
+ * provide a fast-path for small values.
+ */
+#define __put_user(x, ptr) \
+({								\
+	__typeof__(*(ptr)) __x = (x);				\
+	int __pu_err = -EFAULT;					\
+        __chk_user_ptr(ptr);                                    \
+	switch (sizeof (*(ptr))) {				\
+	case 1:							\
+	case 2:							\
+	case 4:							\
+	case 8:							\
+		__pu_err = __put_user_fn(sizeof (*(ptr)),	\
+					 ptr, &__x);		\
+		break;						\
+	default:						\
+		__put_user_bad();				\
+		break;						\
+	 }							\
+	__pu_err;						\
+})
+
+#define put_user(x, ptr)					\
+({								\
+	void __user *__p = (ptr);				\
+	might_fault();						\
+	access_ok(__p, sizeof(*ptr)) ?		\
+		__put_user((x), ((__typeof__(*(ptr)) __user *)__p)) :	\
+		-EFAULT;					\
+})
+
+#ifndef __put_user_fn
+
+static inline int __put_user_fn(size_t size, void __user *ptr, void *x)
+{
+	return unlikely(raw_copy_to_user(ptr, x, size)) ? -EFAULT : 0;
+}
+
+#define __put_user_fn(sz, u, k)	__put_user_fn(sz, u, k)
+
+#endif
+
+extern int __put_user_bad(void) __attribute__((noreturn));
+
+#define __get_user(x, ptr)					\
+({								\
+	int __gu_err = -EFAULT;					\
+	__chk_user_ptr(ptr);					\
+	switch (sizeof(*(ptr))) {				\
+	case 1: {						\
+		unsigned char __x = 0;				\
+		__gu_err = __get_user_fn(sizeof (*(ptr)),	\
+					 ptr, &__x);		\
+		(x) = *(__force __typeof__(*(ptr)) *) &__x;	\
+		break;						\
+	};							\
+	case 2: {						\
+		unsigned short __x = 0;				\
+		__gu_err = __get_user_fn(sizeof (*(ptr)),	\
+					 ptr, &__x);		\
+		(x) = *(__force __typeof__(*(ptr)) *) &__x;	\
+		break;						\
+	};							\
+	case 4: {						\
+		unsigned int __x = 0;				\
+		__gu_err = __get_user_fn(sizeof (*(ptr)),	\
+					 ptr, &__x);		\
+		(x) = *(__force __typeof__(*(ptr)) *) &__x;	\
+		break;						\
+	};							\
+	case 8: {						\
+		unsigned long long __x = 0;			\
+		__gu_err = __get_user_fn(sizeof (*(ptr)),	\
+					 ptr, &__x);		\
+		(x) = *(__force __typeof__(*(ptr)) *) &__x;	\
+		break;						\
+	};							\
+	default:						\
+		__get_user_bad();				\
+		break;						\
+	}							\
+	__gu_err;						\
+})
+
+#define get_user(x, ptr)					\
+({								\
+	const void __user *__p = (ptr);				\
+	might_fault();						\
+	access_ok(__p, sizeof(*ptr)) ?		\
+		__get_user((x), (__typeof__(*(ptr)) __user *)__p) :\
+		((x) = (__typeof__(*(ptr)))0,-EFAULT);		\
+})
+
+#ifndef __get_user_fn
+static inline int __get_user_fn(size_t size, const void __user *ptr, void *x)
+{
+	return unlikely(raw_copy_from_user(x, ptr, size)) ? -EFAULT : 0;
+}
+
+#define __get_user_fn(sz, u, k)	__get_user_fn(sz, u, k)
+
+#endif
+
+extern int __get_user_bad(void) __attribute__((noreturn));
+
+/*
+ * Zero Userspace
+ */
+#ifndef __clear_user
+static inline __must_check unsigned long
+__clear_user(void __user *to, unsigned long n)
+{
+	memset((void __force *)to, 0, n);
+	return 0;
+}
+#endif
+
+static inline __must_check unsigned long
+clear_user(void __user *to, unsigned long n)
+{
+	might_fault();
+	if (!access_ok(to, n))
+		return n;
+
+	return __clear_user(to, n);
+}
+
+#include <asm/extable.h>
+
+__must_check long strncpy_from_user(char *dst, const char __user *src,
+				    long count);
+__must_check long strnlen_user(const char __user *src, long n);
+
+#endif /* __ASM_GENERIC_UACCESS_H */