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    Subject[3.1 patch] x86: default to vsyscall=native
    After upgrading a kernel the existing userspace should just work
    (assuming it did work before ;-) ), but when I upgraded my kernel
    from 3.0.4 to 3.1.0-rc8 a UML instance didn't come up properly.

    dmesg said:
    linux-2.6.30.1[3800] vsyscall fault (exploit attempt?) ip:ffffffffff600000 cs:33 sp:7fbfb9c498 ax:ffffffffff600000 si:0 di:606790
    linux-2.6.30.1[3856] vsyscall fault (exploit attempt?) ip:ffffffffff600000 cs:33 sp:7fbfb13168 ax:ffffffffff600000 si:0 di:606790

    Looking throught the changelog I ended up at commit 3ae36655
    ("x86-64: Rework vsyscall emulation and add vsyscall= parameter").

    Linus suggested in https://lkml.org/lkml/2011/8/9/376 to default to
    vsyscall=native.

    That sounds reasonable to me, and fixes the problem for me.

    Signed-off-by: Adrian Bunk <bunk@kernel.org>
    ---
    Documentation/kernel-parameters.txt | 7 ++++---
    arch/x86/kernel/vsyscall_64.c | 2 +-
    2 files changed, 5 insertions(+), 4 deletions(-)

    diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    index 854ed5ca..d6e6724 100644
    --- a/Documentation/kernel-parameters.txt
    +++ b/Documentation/kernel-parameters.txt
    @@ -2706,10 +2706,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
    functions are at fixed addresses, they make nice
    targets for exploits that can control RIP.

    - emulate [default] Vsyscalls turn into traps and are
    - emulated reasonably safely.
    + emulate Vsyscalls turn into traps and are emulated
    + reasonably safely.

    - native Vsyscalls are native syscall instructions.
    + native [default] Vsyscalls are native syscall
    + instructions.
    This is a little bit faster than trapping
    and makes a few dynamic recompilers work
    better than they would in emulation mode.
    diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
    index 18ae83d..b56c65de 100644
    --- a/arch/x86/kernel/vsyscall_64.c
    +++ b/arch/x86/kernel/vsyscall_64.c
    @@ -56,7 +56,7 @@ DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
    .lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
    };

    -static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;
    +static enum { EMULATE, NATIVE, NONE } vsyscall_mode = NATIVE;

    static int __init vsyscall_setup(char *str)
    {
    --
    1.7.6.3


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