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SubjectRe: [PATCH] arm: fix page faults in do_alignment
On Fri, Aug 30, 2019 at 09:31:17PM +0800, Jing Xiangfeng wrote:
> The function do_alignment can handle misaligned address for user and
> kernel space. If it is a userspace access, do_alignment may fail on
> a low-memory situation, because page faults are disabled in
> probe_kernel_address.
>
> Fix this by using __copy_from_user stead of probe_kernel_address.
>
> Fixes: b255188 ("ARM: fix scheduling while atomic warning in alignment handling code")
> Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>

NAK.

The "scheduling while atomic warning in alignment handling code" is
caused by fixing up the page fault while trying to handle the
mis-alignment fault generated from an instruction in atomic context.

Your patch re-introduces that bug.

> ---
> arch/arm/mm/alignment.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
> index 04b3643..2ccabd3 100644
> --- a/arch/arm/mm/alignment.c
> +++ b/arch/arm/mm/alignment.c
> @@ -774,6 +774,7 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
> unsigned long instr = 0, instrptr;
> int (*handler)(unsigned long addr, unsigned long instr, struct pt_regs *regs);
> unsigned int type;
> + mm_segment_t fs;
> unsigned int fault;
> u16 tinstr = 0;
> int isize = 4;
> @@ -784,16 +785,22 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
>
> instrptr = instruction_pointer(regs);
>
> + fs = get_fs();
> + set_fs(KERNEL_DS);
> if (thumb_mode(regs)) {
> u16 *ptr = (u16 *)(instrptr & ~1);
> - fault = probe_kernel_address(ptr, tinstr);
> + fault = __copy_from_user(tinstr,
> + (__force const void __user *)ptr,
> + sizeof(tinstr));
> tinstr = __mem_to_opcode_thumb16(tinstr);
> if (!fault) {
> if (cpu_architecture() >= CPU_ARCH_ARMv7 &&
> IS_T32(tinstr)) {
> /* Thumb-2 32-bit */
> u16 tinst2 = 0;
> - fault = probe_kernel_address(ptr + 1, tinst2);
> + fault = __copy_from_user(tinst2,
> + (__force const void __user *)(ptr+1),
> + sizeof(tinst2));
> tinst2 = __mem_to_opcode_thumb16(tinst2);
> instr = __opcode_thumb32_compose(tinstr, tinst2);
> thumb2_32b = 1;
> @@ -803,10 +810,13 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
> }
> }
> } else {
> - fault = probe_kernel_address((void *)instrptr, instr);
> + fault = __copy_from_user(instr,
> + (__force const void __user *)instrptr,
> + sizeof(instr));
> instr = __mem_to_opcode_arm(instr);
> }
>
> + set_fs(fs);
> if (fault) {
> type = TYPE_FAULT;
> goto bad_or_fault;
> --
> 1.8.3.1
>
>

--
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