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| author | Xie Yuanbin <xieyuanbin1@huawei.com> | 2026-07-28 03:16:42 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@armlinux.org.uk> | 2026-08-05 16:15:51 +0100 |
| commit | 1039bffd6ae9c75b42b7d148d6c1106134107b66 (patch) | |
| tree | e8ee4ac80f87e2ad1b6b0c877eccbb62b0915c02 /arch/arm/lib/delay-loop.S | |
| download | linux-stable-1039bffd6ae9c75b42b7d148d6c1106134107b66.tar.gz linux-stable-1039bffd6ae9c75b42b7d148d6c1106134107b66.zip | |
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>
Diffstat (limited to 'arch/arm/lib/delay-loop.S')
| -rw-r--r-- | arch/arm/lib/delay-loop.S | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/arch/arm/lib/delay-loop.S b/arch/arm/lib/delay-loop.S new file mode 100644 index 000000000..33b08ca1c --- /dev/null +++ b/arch/arm/lib/delay-loop.S @@ -0,0 +1,67 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * linux/arch/arm/lib/delay.S + * + * Copyright (C) 1995, 1996 Russell King + */ +#include <linux/linkage.h> +#include <linux/cfi_types.h> +#include <asm/assembler.h> +#include <asm/delay.h> + +#ifdef CONFIG_ARCH_RPC + .arch armv4 +#endif + + .text + +.LC0: .word loops_per_jiffy +.LC1: .word UDELAY_MULT + +/* + * loops = r0 * HZ * loops_per_jiffy / 1000000 + * + * r0 <= 2000 + * HZ <= 1000 + */ + +SYM_TYPED_FUNC_START(__loop_udelay) + ldr r2, .LC1 + mul r0, r2, r0 @ r0 = delay_us * UDELAY_MULT + b __loop_const_udelay +SYM_FUNC_END(__loop_udelay) + +SYM_TYPED_FUNC_START(__loop_const_udelay) @ 0 <= r0 <= 0xfffffaf0 + ldr r2, .LC0 + ldr r2, [r2] + umull r1, r0, r2, r0 @ r0-r1 = r0 * loops_per_jiffy + adds r1, r1, #0xffffffff @ rounding up ... + adcs r0, r0, r0 @ and right shift by 31 + reteq lr + b __loop_delay +SYM_FUNC_END(__loop_const_udelay) + + .align 3 + +@ Delay routine +SYM_TYPED_FUNC_START(__loop_delay) + subs r0, r0, #1 +#if 0 + retls lr + subs r0, r0, #1 + retls lr + subs r0, r0, #1 + retls lr + subs r0, r0, #1 + retls lr + subs r0, r0, #1 + retls lr + subs r0, r0, #1 + retls lr + subs r0, r0, #1 + retls lr + subs r0, r0, #1 +#endif + bhi __loop_delay + ret lr +SYM_FUNC_END(__loop_delay) |