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Date:   Tue, 18 Jan 2022 18:56:12 +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>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [RFC PATCH] arm64: don't vmap() invalid page
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On Tue, Jan 18, 2022 at 10:53:54AM -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.
> 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.
> 
> Interestingly, this abort happens even if copy_from_kernel_nofault() is used,
> which is quite inconvenient for debugging purposes. 
> 
> This patch adds an arch_vmap_page_valid() helper into vmap() path, so that
> architectures may add arch-specific checks of the pointer passed into vmap.
> 
> For arm64, if the page passed to vmap() corresponds to a physical address
> greater than maximum possible value as described in TCR_EL1.IPS register, the
> following table walk would generate Address Size Abort. Instead of creating
> the invalid mapping, kernel will return ERANGE in such situation.

This seems like a very elaborate way of spelling:

	pfn_valid(page_to_pfn(page));

which doesn't require any architecture hook.  No?