| The Linux kernel before 2.6.16.9 and the FreeBSD kernel, when running
on AMD64 and other 7th and 8th generation AuthenticAMD processors,
only save/restore the FOP, FIP, and FDP x87 registers in
FXSAVE/FXRSTOR when an exception is pending, which allows one process
to determine portions of the state of floating point instructions of
other processes, which can be leveraged to obtain sensitive
information such as cryptographic keys. NOTE: this is the documented
behavior of AMD64 processors, but it is inconsistent with Intel
processors in a security-relevant fashion that was not addressed by
the kernels.
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