From 1039bffd6ae9c75b42b7d148d6c1106134107b66 Mon Sep 17 00:00:00 2001 From: Xie Yuanbin Date: Tue, 28 Jul 2026 03:16:42 +0100 Subject: ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults 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 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) Reviewed-by: Linus Walleij Signed-off-by: Qi Xi Signed-off-by: Xie Yuanbin Signed-off-by: Russell King --- include/asm-generic/local.h | 57 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) create mode 100644 include/asm-generic/local.h (limited to 'include/asm-generic/local.h') diff --git a/include/asm-generic/local.h b/include/asm-generic/local.h new file mode 100644 index 000000000..7f97018df --- /dev/null +++ b/include/asm-generic/local.h @@ -0,0 +1,57 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_GENERIC_LOCAL_H +#define _ASM_GENERIC_LOCAL_H + +#include +#include +#include + +/* + * A signed long type for operations which are atomic for a single CPU. + * Usually used in combination with per-cpu variables. + * + * This is the default implementation, which uses atomic_long_t. Which is + * rather pointless. The whole point behind local_t is that some processors + * can perform atomic adds and subtracts in a manner which is atomic wrt IRQs + * running on this CPU. local_t allows exploitation of such capabilities. + */ + +/* Implement in terms of atomics. */ + +/* Don't use typedef: don't want them to be mixed with atomic_t's. */ +typedef struct +{ + atomic_long_t a; +} local_t; + +#define LOCAL_INIT(i) { ATOMIC_LONG_INIT(i) } + +#define local_read(l) atomic_long_read(&(l)->a) +#define local_set(l,i) atomic_long_set((&(l)->a),(i)) +#define local_inc(l) atomic_long_inc(&(l)->a) +#define local_dec(l) atomic_long_dec(&(l)->a) +#define local_add(i,l) atomic_long_add((i),(&(l)->a)) +#define local_sub(i,l) atomic_long_sub((i),(&(l)->a)) + +#define local_sub_and_test(i, l) atomic_long_sub_and_test((i), (&(l)->a)) +#define local_dec_and_test(l) atomic_long_dec_and_test(&(l)->a) +#define local_inc_and_test(l) atomic_long_inc_and_test(&(l)->a) +#define local_add_negative(i, l) atomic_long_add_negative((i), (&(l)->a)) +#define local_add_return(i, l) atomic_long_add_return((i), (&(l)->a)) +#define local_sub_return(i, l) atomic_long_sub_return((i), (&(l)->a)) +#define local_inc_return(l) atomic_long_inc_return(&(l)->a) + +#define local_cmpxchg(l, o, n) atomic_long_cmpxchg((&(l)->a), (o), (n)) +#define local_try_cmpxchg(l, po, n) atomic_long_try_cmpxchg((&(l)->a), (po), (n)) +#define local_xchg(l, n) atomic_long_xchg((&(l)->a), (n)) +#define local_add_unless(l, _a, u) atomic_long_add_unless((&(l)->a), (_a), (u)) +#define local_inc_not_zero(l) atomic_long_inc_not_zero(&(l)->a) + +/* Non-atomic variants, ie. preemption disabled and won't be touched + * in interrupt, etc. Some archs can optimize this case well. */ +#define __local_inc(l) local_set((l), local_read(l) + 1) +#define __local_dec(l) local_set((l), local_read(l) - 1) +#define __local_add(i,l) local_set((l), local_read(l) + (i)) +#define __local_sub(i,l) local_set((l), local_read(l) - (i)) + +#endif /* _ASM_GENERIC_LOCAL_H */ -- cgit v1.3.1