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    SubjectRe: [PATCH v2 08/10] x86-64: Emulate vsyscalls

    * Andrew Lutomirski <luto@mit.edu> wrote:

    > On Mon, May 30, 2011 at 3:46 AM, Ingo Molnar <mingo@elte.hu> 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:
    >
    > http://sourceware.org/git/?p=glibc.git;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.

    But only statically built binaries would be impacted in practice,
    right? The number of statically built binaries that heavily rely on
    vsyscalls ought to be a very small set ...

    Thanks,

    Ingo
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