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/scripts/head-object-list.txt b/scripts/head-object-list.txt
new file mode 100644
index 000000000..7274dfc65
--- /dev/null
+++ b/scripts/head-object-list.txt
@@ -0,0 +1,41 @@
+# Head objects
+#
+# The objects listed here are placed at the head of vmlinux. A typical use-case
+# is an object that contains the entry point. This is kept for compatibility
+# with head-y, which Kbuild used to support.
+#
+# A counter approach is to control the section placement by the linker script.
+# The code marked as __HEAD goes into the ".head.text" section, which is placed
+# before the normal ".text" section.
+#
+# If you can achieve the correct code ordering by linker script, please delete
+# the entry from this file.
+#
+arch/alpha/kernel/head.o
+arch/arc/kernel/head.o
+arch/arm/kernel/head-nommu.o
+arch/arm/kernel/head.o
+arch/csky/kernel/head.o
+arch/hexagon/kernel/head.o
+arch/loongarch/kernel/head.o
+arch/m68k/68000/head.o
+arch/m68k/coldfire/head.o
+arch/m68k/kernel/head.o
+arch/m68k/kernel/sun3-head.o
+arch/microblaze/kernel/head.o
+arch/nios2/kernel/head.o
+arch/parisc/kernel/head.o
+arch/powerpc/kernel/head_44x.o
+arch/powerpc/kernel/head_64.o
+arch/powerpc/kernel/head_8xx.o
+arch/powerpc/kernel/head_85xx.o
+arch/powerpc/kernel/head_book3s_32.o
+arch/powerpc/kernel/prom_entry_64.o
+arch/powerpc/kernel/fpu.o
+arch/powerpc/kernel/vector.o
+arch/powerpc/kernel/prom_init.o
+arch/s390/kernel/head64.o
+arch/sh/kernel/head_32.o
+arch/sparc/kernel/head_32.o
+arch/sparc/kernel/head_64.o
+arch/xtensa/kernel/head.o