linux-kernel - Re: [PATCH v2] proc: use untagged_addr() for pagemap

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Date:   Thu, 3 Dec 2020 11:30:21 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Miles Chen <miles.chen@...iatek.com>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, wsd_upstream@...iatek.com,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Marco Elver <elver@...gle.com>, Will Deacon <will@...nel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Song Bao Hua <song.bao.hua@...ilicon.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] proc: use untagged_addr() for pagemap_read addresses

On Fri, Nov 27, 2020 at 01:07:38PM +0800, Miles Chen wrote:
> Cc: Will Deacon <will.deacon@....com>

That should be will@...nel.org.

> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 217aa2705d5d..92b277388f05 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1599,11 +1599,15 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
>  
>  	src = *ppos;
>  	svpfn = src / PM_ENTRY_BYTES;
> -	start_vaddr = svpfn << PAGE_SHIFT;
>  	end_vaddr = mm->task_size;
>  
>  	/* watch out for wraparound */
> -	if (svpfn > mm->task_size >> PAGE_SHIFT)
> +	start_vaddr = end_vaddr;
> +	if (svpfn < (ULONG_MAX >> PAGE_SHIFT))

Does this need to be strict less-than? I think a less-than or equal
would work better.

> +		start_vaddr = untagged_addr(svpfn << PAGE_SHIFT);
> +
> +	/* Ensure the address is inside the task */
> +	if (start_vaddr > mm->task_size)
>  		start_vaddr = end_vaddr;

Otherwise the logic looks fine to me. With the above:

Reviewed-by: Catalin Marinas <catalin.marinas@....com>