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ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults

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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: 6d021b7244 ("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>
This commit is contained in:
Xie Yuanbin 2026-07-28 03:16:42 +01:00 committed by Russell King
parent e79ca91165
commit 1039bffd6a
1 changed files with 14 additions and 2 deletions
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16
arch/arm/mm/fault.c
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@ -181,7 +181,11 @@ __do_user_fault(unsigned long addr, unsigned int fsr, unsigned int sig,
pr_err("8<--- cut here ---\n");
pr_err("%s: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
tsk->comm, sig, addr, fsr);
show_pte(KERN_ERR, tsk->mm, addr);
if (likely(addr < TASK_SIZE)) {
mmap_write_lock(tsk->mm);
show_pte(KERN_ERR, tsk->mm, addr);
mmap_write_unlock(tsk->mm);
}
show_regs(regs);
}
#endif
@ -639,7 +643,15 @@ do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
pr_alert("8<--- cut here ---\n");
pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
inf->name, fsr, addr);
show_pte(KERN_ALERT, current->mm, addr);
if (likely(user_mode(regs))) {
if (addr < TASK_SIZE) {
mmap_write_lock(current->mm);
show_pte(KERN_ALERT, current->mm, addr);
mmap_write_unlock(current->mm);
}
} else {
show_pte(KERN_ALERT, current->mm, addr);
}
arm_notify_die("", regs, inf->sig, inf->code, (void __user *)addr,
fsr, 0);