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Date:   Fri, 1 May 2020 14:09:20 +0000
From:   "Luck, Tony" <>
To:     Andy Lutomirski <>,
        Linus Torvalds <>
CC:     "Williams, Dan J" <>,
        Andy Lutomirski <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        Peter Zijlstra <>,
        Borislav Petkov <>,
        stable <>,
        the arch/x86 maintainers <>,
        "H. Peter Anvin" <>,
        Paul Mackerras <>,
        Benjamin Herrenschmidt <>,
        "Tsaur, Erwin" <>,
        Michael Ellerman <>,
        Arnaldo Carvalho de Melo <>,
        linux-nvdimm <>,
        Linux Kernel Mailing List <>
Subject: RE: [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe()

> Now maybe copy_to_user() should *always* work this way, but I’m not convinced.
> Certainly put_user() shouldn’t — the result wouldn’t even be well defined. And I’m
>  unconvinced that it makes much sense for the majority of copy_to_user() callers
>  that are also directly accessing the source structure.

One case that might work is copy_to_user() that's copying from the kernel page cache
to the user in response to a read(2) system call.  Action would be to check if we could
re-read from the file system to a different page. If not, return -EIO. Either way ditch the
poison page from the page cache.


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