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, 25 insertions, 0 deletions

diff --git a/arch/alpha/boot/bootloader.lds b/arch/alpha/boot/bootloader.lds
new file mode 100644
index 000000000..8cdff54c6
--- /dev/null
+++ b/arch/alpha/boot/bootloader.lds
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+OUTPUT_FORMAT("elf64-alpha")
+ENTRY(__start)
+printk = srm_printk;
+SECTIONS
+{
+  . = 0x20000000;
+  .text : { *(.text) }
+  _etext = .;
+  PROVIDE (etext = .);
+  .rodata : { *(.rodata) *(.rodata.*) }
+  .data : { *(.data) CONSTRUCTORS }
+  .got : { *(.got) }
+  .sdata : { *(.sdata) }
+  _edata = .;
+  PROVIDE (edata = .);
+  .sbss : { *(.sbss) *(.scommon) }
+  .bss : { *(.bss) *(COMMON) }
+  _end = . ;
+  PROVIDE (end = .);
+
+  .mdebug 0 : { *(.mdebug) }
+  .note 0 : { *(.note) }
+  .comment 0 : { *(.comment) }
+}