linux-kernel - Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery

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Date:   Sun, 22 Aug 2021 16:46:14 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Jue Wang <juew@...gle.com>, Ding Hui <dinghui@...gfor.com.cn>,
        naoya.horiguchi@....com, osalvador@...e.de,
        Youquan Song <youquan.song@...el.com>, huangcun@...gfor.com.cn,
        x86@...nel.org, linux-edac@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user
 recovery

On Fri, Aug 20, 2021 at 01:33:56PM -0700, Luck, Tony wrote:
> The new version (thanks to All fixing iov_iter.c) now does
> exactly what POSIX says should happen.  If I have a buffer
> with poison at offset 213, and I do this:
> 
> 	ret = write(fd, buf, 512);
> 
> Then the return from write is 213, and the first 213 bytes
> from the buffer appear in the file, and the file size is
> incremented by 213 (assuming the write started with the lseek
> offset at the original size of the file).

... and the user still gets a SIGBUS so that it gets a chance to handle
the encountered poison? I.e., not retry the write for the remaining 512
- 213 bytes?

If so, do we document that somewhere so that application writers can
know what they should do in such cases?

-- 
Regards/Gruss,
    Boris.

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