linux-kernel - Re: [PATCH v2 2/6] arm64/vdso: Zap vvar pages when switching to a time namespace

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Message-ID: <b56f9232-1914-4c7a-7aac-76207fb989c5@arm.com>
Date:   Thu, 9 Apr 2020 13:01:52 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Andrei Vagin <avagin@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH v2 2/6] arm64/vdso: Zap vvar pages when switching to a
 time namespace

On 2/25/20 7:37 AM, Andrei Vagin wrote:
> The VVAR page layout depends on whether a task belongs to the root or
> non-root time namespace. Whenever a task changes its namespace, the VVAR
> page tables are cleared and then they will be re-faulted with a
> corresponding layout.
> 
> Signed-off-by: Andrei Vagin <avagin@...il.com>

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>

> ---
>  arch/arm64/kernel/vdso.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> index 290c36d74e03..6ac9cdeac5be 100644
> --- a/arch/arm64/kernel/vdso.c
> +++ b/arch/arm64/kernel/vdso.c
> @@ -131,6 +131,38 @@ static int __vdso_init(enum arch_vdso_type arch_index)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_TIME_NS
> +/*
> + * The vvar page layout depends on whether a task belongs to the root or
> + * non-root time namespace. Whenever a task changes its namespace, the VVAR
> + * page tables are cleared and then they will re-faulted with a
> + * corresponding layout.
> + * See also the comment near timens_setup_vdso_data() for details.
> + */
> +int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
> +{
> +	struct mm_struct *mm = task->mm;
> +	struct vm_area_struct *vma;
> +
> +	if (down_write_killable(&mm->mmap_sem))
> +		return -EINTR;
> +
> +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +		unsigned long size = vma->vm_end - vma->vm_start;
> +
> +		if (vma_is_special_mapping(vma, vdso_lookup[ARM64_VDSO].dm))
> +			zap_page_range(vma, vma->vm_start, size);
> +#ifdef CONFIG_COMPAT_VDSO
> +		if (vma_is_special_mapping(vma, vdso_lookup[ARM64_VDSO32].dm))
> +			zap_page_range(vma, vma->vm_start, size);
> +#endif
> +	}
> +
> +	up_write(&mm->mmap_sem);
> +	return 0;
> +}
> +#endif
> +
>  static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
>  			     struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
> 

-- 
Regards,
Vincenzo