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    SubjectRe: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode
    On Mon, May 08, 2017 at 04:06:35PM +0200, Jann Horn wrote:

    > I think Kees might be talking about
    > https://bugs.chromium.org/p/project-zero/issues/detail?id=822, fixed in
    > commit e6978e4bf181fb3b5f8cb6f71b4fe30fbf1b655c. The issue was that
    > perf code that can run in pretty much any context called access_ok().

    And that commit has *NOT* solved the problem. perf_callchain_user()
    can be called synchronously, without passing through that code.
    Tracepoint shite...

    That set_fs() should be done in get_perf_callchain(), just around the call of
    perf_callchain_user(). Along with pagefault_disable(), actually.

    BTW, that's a nice example demonstrating why doing that on the kernel
    boundary is wrong. Wider (in theory) area being "protected" => easier
    to miss the ways not crossing its border.

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