• Thomas Gleixner's avatar
    prctl: Add speculation control prctls · b617cfc8
    Thomas Gleixner authored
    
    
    Add two new prctls to control aspects of speculation related vulnerabilites
    and their mitigations to provide finer grained control over performance
    impacting mitigations.
    
    PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature
    which is selected with arg2 of prctl(2). The return value uses bit 0-2 with
    the following meaning:
    
    Bit  Define           Description
    0    PR_SPEC_PRCTL    Mitigation can be controlled per task by
                          PR_SET_SPECULATION_CTRL
    1    PR_SPEC_ENABLE   The speculation feature is enabled, mitigation is
                          disabled
    2    PR_SPEC_DISABLE  The speculation feature is disabled, mitigation is
                          enabled
    
    If all bits are 0 the CPU is not affected by the speculation misfeature.
    
    If PR_SPEC_PRCTL is set, then the per task control of the mitigation is
    available. If not set, prctl(PR_SET_SPECULATION_CTRL) for the speculation
    misfeature will fail.
    
    PR_SET_SPECULATION_CTRL allows to control the speculation misfeature, which
    is selected by arg2 of prctl(2) per task. arg3 is used to hand in the
    control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE.
    
    The common return values are:
    
    EINVAL  prctl is not implemented by the architecture or the unused prctl()
            arguments are not 0
    ENODEV  arg2 is selecting a not supported speculation misfeature
    
    PR_SET_SPECULATION_CTRL has these additional return values:
    
    ERANGE  arg3 is incorrect, i.e. it's not either PR_SPEC_ENABLE or PR_SPEC_DISABLE
    ENXIO   prctl control of the selected speculation misfeature is disabled
    
    The first supported controlable speculation misfeature is
    PR_SPEC_STORE_BYPASS. Add the define so this can be shared between
    architectures.
    
    Based on an initial patch from Tim Chen and mostly rewritten.
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
    Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    b617cfc8