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[Bug 1597971] [NEW] kernel: signal return with invalid floating-point control


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Please backport:
commit bcf4dd5f9ee096bd1510f838dd4750c35df4e38b
Author: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Date:   Mon Jun 27 17:06:45 2016 +0200

    s390: fix test_fp_ctl inline assembly contraints
    The test_fp_ctl function is used to test if a given value is a valid
    floating-point control. The inline assembly in test_fp_ctl uses an
    incorrect constraint for the 'orig_fpc' variable. If the compiler
    chooses the same register for 'fpc' and 'orig_fpc' the test_fp_ctl()
    function always returns true. This allows user space to trigger
    kernel oopses with invalid floating-point control values on the
    signal stack.
    This problem has been introduced with git commit 4725c86055f5bbdcdf
    "s390: fix save and restore of the floating-point-control register"
    Cc: stable@xxxxxxxxxxxxxxx # v3.13+
    Reviewed-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
    Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

** Affects: linux (Ubuntu)
     Importance: Undecided
     Assignee: Skipper Bug Screeners (skipper-screen-team)
         Status: New

** Tags: architecture-s39064 bugnameltc-143266 severity-high targetmilestone-inin1604
kernel: signal return with invalid floating-point control
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