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    Subject[PATCH 4.4 08/45] x86/vdso: Ensure vdso32_enabled gets set to valid values only
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mathias Krause <minipli@googlemail.com>

    commit c06989da39cdb10604d572c8c7ea8c8c97f3c483 upstream.

    vdso_enabled can be set to arbitrary integer values via the kernel command
    line 'vdso32=' parameter or via 'sysctl abi.vsyscall32'.

    load_vdso32() only maps VDSO if vdso_enabled == 1, but ARCH_DLINFO_IA32
    merily checks for vdso_enabled != 0. As a consequence the AT_SYSINFO_EHDR
    auxiliary vector for the VDSO_ENTRY is emitted with a NULL pointer which
    causes a segfault when the application tries to use the VDSO.

    Restrict the valid arguments on the command line and the sysctl to 0 and 1.

    Fixes: b0b49f2673f0 ("x86, vdso: Remove compat vdso support")
    Signed-off-by: Mathias Krause <minipli@googlemail.com>
    Acked-by: Andy Lutomirski <luto@amacapital.net>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Roland McGrath <roland@redhat.com>
    Link: http://lkml.kernel.org/r/1491424561-7187-1-git-send-email-minipli@googlemail.com
    Link: http://lkml.kernel.org/r/20170410151723.518412863@linutronix.de
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/entry/vdso/vdso32-setup.c | 11 +++++++++--
    1 file changed, 9 insertions(+), 2 deletions(-)

    --- a/arch/x86/entry/vdso/vdso32-setup.c
    +++ b/arch/x86/entry/vdso/vdso32-setup.c
    @@ -31,8 +31,10 @@ static int __init vdso32_setup(char *s)
    {
    vdso32_enabled = simple_strtoul(s, NULL, 0);

    - if (vdso32_enabled > 1)
    + if (vdso32_enabled > 1) {
    pr_warn("vdso32 values other than 0 and 1 are no longer allowed; vdso disabled\n");
    + vdso32_enabled = 0;
    + }

    return 1;
    }
    @@ -63,13 +65,18 @@ subsys_initcall(sysenter_setup);
    /* Register vsyscall32 into the ABI table */
    #include <linux/sysctl.h>

    +static const int zero;
    +static const int one = 1;
    +
    static struct ctl_table abi_table2[] = {
    {
    .procname = "vsyscall32",
    .data = &vdso32_enabled,
    .maxlen = sizeof(int),
    .mode = 0644,
    - .proc_handler = proc_dointvec
    + .proc_handler = proc_dointvec_minmax,
    + .extra1 = (int *)&zero,
    + .extra2 = (int *)&one,
    },
    {}
    };

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