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Date:   Wed, 19 Jan 2022 00:51:27 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Ding Tianhong <dingtianhong@huawei.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Alexey Klimov <aklimov@redhat.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Uladzislau Rezki <urezki@gmail.com>
Subject: Re: [PATCH] vmap(): don't allow invalid pages
Message-ID: <Yedgj+Lo2eru8197@casper.infradead.org>
References: <20220118235244.540103-1-yury.norov@gmail.com>
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On Tue, Jan 18, 2022 at 03:52:44PM -0800, Yury Norov wrote:
> vmap() takes struct page *pages as one of arguments, and user may provide
> an invalid pointer which would lead to DABT at address translation later.

Could we spell out 'DABT'?  Presumably that's an ARM-specific thing.
Just like we don't say #PF for Intel page faults, I think this is
probably a 'data abort'?

> Currently, kernel checks the pages against NULL. In my case, however, the
> address was not NULL, and was big enough so that the hardware generated
> Address Size Abort on arm64.
> 
> Interestingly, this abort happens even if copy_from_kernel_nofault() is
> used, which is quite inconvenient for debugging purposes. 
> 
> This patch adds a pfn_valid() check into vmap() path, so that invalid
> mapping will not be created.
> 
> RFC: https://lkml.org/lkml/2022/1/18/815
> v1: use pfn_valid() instead of adding an arch-specific
>     arch_vmap_page_valid(). Thanks to Matthew Wilcox for the hint.
> 
> Signed-off-by: Yury Norov <yury.norov@gmail.com>

Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>

> ---
>  mm/vmalloc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d2a00ad4e1dd..a4134ee56b10 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -477,6 +477,8 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr,
>  			return -EBUSY;
>  		if (WARN_ON(!page))
>  			return -ENOMEM;
> +		if (WARN_ON(!pfn_valid(page_to_pfn(page))))
> +			return -EINVAL;
>  		set_pte_at(&init_mm, addr, pte, mk_pte(page, prot));
>  		(*nr)++;
>  	} while (pte++, addr += PAGE_SIZE, addr != end);
> -- 
> 2.30.2
>