FreeBSD -- FPU information disclosure

Problem Description
On “7th generation” and “8th generation” processors
manufactured by AMD, including the AMD Athlon, Duron, Athlon
MP, Athlon XP, Athlon64, Athlon64 FX, Opteron, Turion, and
Sempron, the fxsave and fxrstor instructions do not save and
restore the FOP, FIP, and FDP registers unless the exception
summary bit (ES) in the x87 status word is set to 1,
indicating that an unmasked x87 exception has occurred.
This behaviour is consistent with documentation provided by
AMD, but is different from processors from other vendors,
which save and restore the FOP, FIP, and FDP registers
regardless of the value of the ES bit. As a result of this
discrepancy remaining unnoticed until now, the FreeBSD kernel
does not restore the contents of the FOP, FIP, and FDP
registers between context switches.
Impact
On affected processors, a local attacker can monitor the
execution path of a process which uses floating-point
operations. This may allow an attacker to steal
cryptographic keys or other sensitive information.
Workaround
No workaround is available, but systems which do not use AMD
Athlon, Duron, Athlon MP, Athlon XP, Athlon64, Athlon64 FX,
Opteron, Turion, or Sempron processors are not vulnerable.