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 --- .../userspace-api/ioctl/ioctl-decoding.rst | 31 ++++++++++++++++++++++ 1 file changed, 31 insertions(+) create mode 100644 Documentation/userspace-api/ioctl/ioctl-decoding.rst (limited to 'Documentation/userspace-api/ioctl/ioctl-decoding.rst') diff --git a/Documentation/userspace-api/ioctl/ioctl-decoding.rst b/Documentation/userspace-api/ioctl/ioctl-decoding.rst new file mode 100644 index 000000000..380d6bb3e --- /dev/null +++ b/Documentation/userspace-api/ioctl/ioctl-decoding.rst @@ -0,0 +1,31 @@ +============================== +Decoding an IOCTL Magic Number +============================== + +To decode a hex IOCTL code: + +Most architectures use this generic format, but check +include/ARCH/ioctl.h for specifics, e.g. powerpc +uses 3 bits to encode read/write and 13 bits for size. + + ====== ================================== + bits meaning + ====== ================================== + 31-30 00 - no parameters: uses _IO macro + 10 - read: _IOR + 01 - write: _IOW + 11 - read/write: _IOWR + + 29-16 size of arguments + + 15-8 ascii character supposedly + unique to each driver + + 7-0 function # + ====== ================================== + + +So for example 0x82187201 is a read with arg length of 0x218, +character 'r' function 1. Grepping the source reveals this is:: + + #define VFAT_IOCTL_READDIR_BOTH _IOR('r', 1, struct dirent [2]) -- cgit v1.3.1