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    Subject[PATCH] UML - host VDSO fix
    This fixes a problem seen by a number of people running UML on newer host
    kernels. init would hang with an infinite segfault loop.

    It turns out that the host kernel was providing a AT_SYSINFO_EHDR of
    0xffffe000, which faked UML into believing that the host VDSO page could be
    reused. However, AT_SYSINFO pointed into the middle of the address space, and
    was unmapped as a result. Because UML was providing AT_SYSINFO_EHDR and
    AT_SYSINFO to its own processes, these would branch to nowhere when trying to
    use the VDSO.

    The fix is to also check the location of AT_SYSINFO when deciding whether to
    use the host's VDSO.

    Signed-off-by: Jeff Dike <jdike@linux.intel.com>
    --
    arch/um/os-Linux/elf_aux.c | 3 +++
    1 file changed, 3 insertions(+)

    Index: linux-2.6.17/arch/um/os-Linux/elf_aux.c
    ===================================================================
    --- linux-2.6.17.orig/arch/um/os-Linux/elf_aux.c 2007-02-23 15:00:51.000000000 -0500
    +++ linux-2.6.17/arch/um/os-Linux/elf_aux.c 2007-02-23 15:09:58.000000000 -0500
    @@ -39,6 +39,9 @@ __init void scan_elf_aux( char **envp)
    switch ( auxv->a_type ) {
    case AT_SYSINFO:
    __kernel_vsyscall = auxv->a_un.a_val;
    + /* See if the page is under TASK_SIZE */
    + if (__kernel_vsyscall < (unsigned long) envp)
    + __kernel_vsyscall = 0;
    break;
    case AT_SYSINFO_EHDR:
    vsyscall_ehdr = auxv->a_un.a_val;
    -
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