Messages in this thread | | | Date | Fri, 28 Feb 1997 16:49:51 +0100 (MET) | From | Stephan Meyer <> | Subject | Re: x86 MSRs - example program |
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On Fri, 28 Feb 1997, Philippe Strauss wrote: > Reading some doco about RDTSC and RDMSR, I just learn that RDTSC is only > available in ring 0.. (At least Therje Matiesen wrote that in his Byte > article). I'm using RDTSC from user space since a while in a FFT > benchmarking software, i just wonder how it is possible ? > > my software can be found here: > ftp://sicel-home-1-4.urbanet.ch/pub/XSpectrum-1.1.tar.gz > > Needless to say that i own an intel pentium.
This is from an Intel manual: In the special register "cr4" bit number 3 decides over this. If the bit is set (orl $4,%%cr4), executing RDTSC in any cpl!=0 gives a GPF. IMHO this should be done in ./arch/i386/kernel/head.S or setup.c . Maybe I'm being paranoid here, but this could be a security hole of some type.
Cheers, Stephan
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