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/uapi/asm-generic/ipcbuf.h | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) create mode 100644 include/uapi/asm-generic/ipcbuf.h (limited to 'include/uapi/asm-generic/ipcbuf.h') diff --git a/include/uapi/asm-generic/ipcbuf.h b/include/uapi/asm-generic/ipcbuf.h new file mode 100644 index 000000000..41a01b494 --- /dev/null +++ b/include/uapi/asm-generic/ipcbuf.h @@ -0,0 +1,37 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef __ASM_GENERIC_IPCBUF_H +#define __ASM_GENERIC_IPCBUF_H + +#include + +/* + * The generic ipc64_perm structure: + * Note extra padding because this structure is passed back and forth + * between kernel and user space. + * + * ipc64_perm was originally meant to be architecture specific, but + * everyone just ended up making identical copies without specific + * optimizations, so we may just as well all use the same one. + * + * Pad space is left for: + * - 32-bit mode_t on architectures that only had 16 bit + * - 32-bit seq + * - 2 miscellaneous 32-bit values + */ + +struct ipc64_perm { + __kernel_key_t key; + __kernel_uid32_t uid; + __kernel_gid32_t gid; + __kernel_uid32_t cuid; + __kernel_gid32_t cgid; + __kernel_mode_t mode; + /* pad if mode_t is u16: */ + unsigned char __pad1[4 - sizeof(__kernel_mode_t)]; + unsigned short seq; + unsigned short __pad2; + __kernel_ulong_t __unused1; + __kernel_ulong_t __unused2; +}; + +#endif /* __ASM_GENERIC_IPCBUF_H */ -- cgit v1.3.1