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    SubjectRe: [PATCH v2 08/10] x86-64: Emulate vsyscalls
    On Mon, May 30, 2011 at 3:46 AM, Ingo Molnar <> wrote:
    > * Andy Lutomirski <luto@MIT.EDU> wrote:
    >> There's a fair amount of code in the vsyscall page, and who knows
    >> what will happen if an exploit jumps into the middle of it.  Reduce
    >> the risk by replacing most of it with short magic incantations that
    >> are useless if entered in the middle.  This change can be disabled
    >> by CONFIG_UNSAFE_VSYSCALLS (default y).
    > btw., please flip the default or consider removing the option
    > altogether.
    > We want to improve security and we want safe vsyscalls the default,
    > and it's no good if we make it too easy for users to keep the fire
    > door open all the time! :-)

    I'd advocate waiting until glibc 2.14 comes out with this change:;a=commit;h=a8509ca540427502bd955f35296ff7b727c7a8a1

    I want to add a warning (ratelimited to an extremely low rate) in v3
    whenever any of the vsyscalls get used telling users that their legacy
    code is suffering a performance impact, but it seems like bad form to
    tell people to build glibc from git to avoid a regression.

    The other option is to make the change unconditional for gettimeofday
    and vgetcpu but leave time alone for awhile. There's no a priori
    reason why leaving vtime around is worse than vread_tsc and

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