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, 41 insertions, 0 deletions

diff --git a/include/asm-generic/module.h b/include/asm-generic/module.h
new file mode 100644
index 000000000..a8622501b
--- /dev/null
+++ b/include/asm-generic/module.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_MODULE_H
+#define __ASM_GENERIC_MODULE_H
+
+/*
+ * Many architectures just need a simple module
+ * loader without arch specific data.
+ */
+#ifndef CONFIG_HAVE_MOD_ARCH_SPECIFIC
+struct mod_arch_specific
+{
+};
+#endif
+
+#ifdef CONFIG_64BIT
+#define Elf_Shdr	Elf64_Shdr
+#define Elf_Phdr	Elf64_Phdr
+#define Elf_Sym		Elf64_Sym
+#define Elf_Dyn		Elf64_Dyn
+#define Elf_Ehdr	Elf64_Ehdr
+#define Elf_Addr	Elf64_Addr
+#define Elf_Rel		Elf64_Rel
+#define Elf_Rela	Elf64_Rela
+#define ELF_R_TYPE(X)	ELF64_R_TYPE(X)
+#define ELF_R_SYM(X)	ELF64_R_SYM(X)
+
+#else /* CONFIG_64BIT */
+
+#define Elf_Shdr	Elf32_Shdr
+#define Elf_Phdr	Elf32_Phdr
+#define Elf_Sym		Elf32_Sym
+#define Elf_Dyn		Elf32_Dyn
+#define Elf_Ehdr	Elf32_Ehdr
+#define Elf_Addr	Elf32_Addr
+#define Elf_Rel		Elf32_Rel
+#define Elf_Rela	Elf32_Rela
+#define ELF_R_TYPE(X)	ELF32_R_TYPE(X)
+#define ELF_R_SYM(X)	ELF32_R_SYM(X)
+#endif
+
+#endif /* __ASM_GENERIC_MODULE_H */