linux-kernel - Re: [RFC PATCH -next V3 2/6] arm64: fix types in copy

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Date:   Tue, 12 Apr 2022 19:50:38 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Tong Tiangen <tongtiangen@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Robin Murphy <robin.murphy@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Alexander Viro" <viro@...iv.linux.org.uk>, <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        Xie XiuQi <xiexiuqi@...wei.com>
Subject: Re: [RFC PATCH -next V3 2/6] arm64: fix types in copy_highpage()


On 2022/4/12 15:25, Tong Tiangen wrote:
> In copy_highpage() the `kto` and `kfrom` local variables are pointers to
> struct page, but these are used to hold arbitrary pointers to kernel memory
> . Each call to page_address() returns a void pointer to memory associated
> with the relevant page, and copy_page() expects void pointers to this
> memory.
>
> This inconsistency was introduced in commit 2563776b41c3 ("arm64: mte:
> Tags-aware copy_{user_,}highpage() implementations") and while this
> doesn't appear to be harmful in practice it is clearly wrong.
>
> Correct this by making `kto` and `kfrom` void pointers.
Reviewed-by: Kefeng Wang <wangkefeng.wang@...wei.com>

> Fixes: 2563776b41c3 ("arm64: mte: Tags-aware copy_{user_,}highpage() implementations")
> Signed-off-by: Tong Tiangen <tongtiangen@...wei.com>
> Acked-by: Mark Rutland <mark.rutland@....com>
> ---
>   arch/arm64/mm/copypage.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c
> index b5447e53cd73..0dea80bf6de4 100644
> --- a/arch/arm64/mm/copypage.c
> +++ b/arch/arm64/mm/copypage.c
> @@ -16,8 +16,8 @@
>   
>   void copy_highpage(struct page *to, struct page *from)
>   {
> -	struct page *kto = page_address(to);
> -	struct page *kfrom = page_address(from);
> +	void *kto = page_address(to);
> +	void *kfrom = page_address(from);
>   
>   	copy_page(kto, kfrom);
>