linux-kernel - Re: [BUG] arm64: an infinite loop in generic_perform

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Message-ID: <YNKhjkuzXEJrBUA8@zeniv-ca.linux.org.uk>
Date:   Wed, 23 Jun 2021 02:50:54 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Chen Huang <chenhuang5@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mm <linux-mm@...ck.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] arm64: an infinite loop in generic_perform_write()

On Wed, Jun 23, 2021 at 10:39:31AM +0800, Chen Huang wrote:

> Then when kernel handles the alignment_fault, it will not panic. As the
> arm64 memory model spec said, when the address is not a multiple of the
> element size, the access is unaligned. Unaligned accesses are allowed to
> addresses marked as Normal, but not to Device regions. An unaligned access
> to a Device region will trigger an exception (alignment fault).
> 	
> do_alignment_fault
>     do_bad_area
> 	__do_kernel_fault
>            fixup_exception
> 
> But that fixup cann't handle the unaligned copy, so the
> copy_page_from_iter_atomic returns 0 and traps in loop.

Looks like you need to fix your raw_copy_from_user(), then...