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, 37 insertions, 0 deletions

diff --git a/drivers/video/fbdev/atafb.h b/drivers/video/fbdev/atafb.h
new file mode 100644
index 000000000..2b2675980
--- /dev/null
+++ b/drivers/video/fbdev/atafb.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _VIDEO_ATAFB_H
+#define _VIDEO_ATAFB_H
+
+void atafb_mfb_copyarea(struct fb_info *info, u_long next_line, int sy, int sx, int dy,
+			int dx, int height, int width);
+void atafb_mfb_fillrect(struct fb_info *info, u_long next_line, u32 color,
+			int sy, int sx, int height, int width);
+void atafb_mfb_linefill(struct fb_info *info, u_long next_line,
+			int dy, int dx, u32 width,
+			const u8 *data, u32 bgcolor, u32 fgcolor);
+
+void atafb_iplan2p2_copyarea(struct fb_info *info, u_long next_line, int sy, int sx, int dy,
+			     int dx, int height, int width);
+void atafb_iplan2p2_fillrect(struct fb_info *info, u_long next_line, u32 color,
+			     int sy, int sx, int height, int width);
+void atafb_iplan2p2_linefill(struct fb_info *info, u_long next_line,
+			     int dy, int dx, u32 width,
+			     const u8 *data, u32 bgcolor, u32 fgcolor);
+
+void atafb_iplan2p4_copyarea(struct fb_info *info, u_long next_line, int sy, int sx, int dy,
+			     int dx, int height, int width);
+void atafb_iplan2p4_fillrect(struct fb_info *info, u_long next_line, u32 color,
+			     int sy, int sx, int height, int width);
+void atafb_iplan2p4_linefill(struct fb_info *info, u_long next_line,
+			     int dy, int dx, u32 width,
+			     const u8 *data, u32 bgcolor, u32 fgcolor);
+
+void atafb_iplan2p8_copyarea(struct fb_info *info, u_long next_line, int sy, int sx, int dy,
+			     int dx, int height, int width);
+void atafb_iplan2p8_fillrect(struct fb_info *info, u_long next_line, u32 color,
+			     int sy, int sx, int height, int width);
+void atafb_iplan2p8_linefill(struct fb_info *info, u_long next_line,
+			     int dy, int dx, u32 width,
+			     const u8 *data, u32 bgcolor, u32 fgcolor);
+
+#endif /* _VIDEO_ATAFB_H */