• Andi Kleen's avatar
    x86/speculation/mds: Add basic bug infrastructure for MDS · ffbf5671
    Andi Kleen authored
    commit ed5194c2 upstream
    
    Microarchitectural Data Sampling (MDS), is a class of side channel attacks
    on internal buffers in Intel CPUs. The variants are:
    
     - Microarchitectural Store Buffer Data Sampling (MSBDS) (CVE-2018-12126)
     - Microarchitectural Fill Buffer Data Sampling (MFBDS) (CVE-2018-12130)
     - Microarchitectural Load Port Data Sampling (MLPDS) (CVE-2018-12127)
    
    MSBDS leaks Store Buffer Entries which can be speculatively forwarded to a
    dependent load (store-to-load forwarding) as an optimization. The forward
    can also happen to a faulting or assisting load operation for a different
    memory address, which can be exploited under certain conditions. Store
    buffers are partitioned between Hyper-Threads so cross thread forwarding is
    not possible. But if a thread enters or exits a sleep state the store
    buffer is repartitioned which can expose data from one thread to the other.
    
    MFBDS leaks Fill Buffer Entries. Fill buffers are used internally to manage
    L1 miss situations and to hold data which is returned or sent in response
    to a memory or I/O operation. Fill buffers can forward data to a load
    operation and also write data to the cache. When the fill buffer is
    deallocated it can retain the stale data of the preceding operations which
    can then be forwarded to a faulting or assisting load operation, which can
    be exploited under certain conditions. Fill buffers are shared between
    Hyper-Threads so cross thread leakage is possible.
    
    MLDPS leaks Load Port Data. Load ports are used to perform load operations
    from memory or I/O. The received data is then forwarded to the register
    file or a subsequent operation. In some implementations the Load Port can
    contain stale data from a previous operation which can be forwarded to
    faulting or assisting loads under certain conditions, which again can be
    exploited eventually. Load ports are shared between Hyper-Threads so cross
    thread leakage is possible.
    
    All variants have the same mitigation for single CPU thread case (SMT off),
    so the kernel can treat them as one MDS issue.
    
    Add the basic infrastructure to detect if the current CPU is affected by
    MDS.
    
    [ tglx: Rewrote changelog ]
    Signed-off-by: default avatarAndi Kleen <ak@linux.intel.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Reviewed-by: default avatarBorislav Petkov <bp@suse.de>
    Reviewed-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
    Reviewed-by: default avatarJon Masters <jcm@redhat.com>
    Tested-by: default avatarJon Masters <jcm@redhat.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    ffbf5671
common.c 47.8 KB