Info on Test Registers

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vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid

Hi guys, do you know some good source of info on Test Registers (TR6, TR7)?

Particulary, I am interested in direct access to Branch Target Buffer, which should be supposedly possible via Test Registers.

05 Oct 2008, 18:31

DJ Mauretto

Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy

DJ Mauretto

Ciao

Try this http://www.jalix.org/ressources/miscellaneous/~vrac/faqsys/docs/pentium.txt
Test registers tr0 tr7 (386/486) don't exist anymore,in this document
there are model specific registers of pentium among them are 12 test registers
I do not think that standard.

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Nil Volentibus Arduum Razz

05 Oct 2008, 19:44

DJ Mauretto

Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy

DJ Mauretto

Read 10.6.2 section of intel386 manual for original test registers TR6 TR7 Wink

http://www.x86.org/intel.doc/386manuals.htm

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Nil Volentibus Arduum Razz

06 Oct 2008, 09:36

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid

I asked Agner Fog about this, and he told me direct access to BTB is only possible on old pentiums.

06 Oct 2008, 10:24

tom tobias

Joined: 09 Sep 2003
Posts: 1320
Location: usa

tom tobias

vid wrote:

...I am interested in direct access to Branch Target Buffer...

My understanding is that access to the BTB is sought in those situations in which one seeks to identify the out of order sequence of instructions, i.e. dynamic execution. I am unable to comprehend how the quest for that information relates to UEFI. Does some malware seek to disrupt the normal sequence of issuance of instructions?

Confused

06 Oct 2008, 11:40

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid

Quote:

Does some malware seek to disrupt the normal sequence of issuance of instructions?

No... I don't want to talk about this too much now, it's just an idea I will try to follow. Some time later i will publish all the stuff ready for pleasant reading.

06 Oct 2008, 16:52

IceStudent

Joined: 19 Dec 2003
Posts: 60
Location: Ukraine

IceStudent

vid wrote:

Particulary, I am interested in direct access to Branch Target Buffer, which should be supposedly possible via Test Registers.

Why not to use the MSR registers for it? You can to do it even in ring-3, via the NtSystemDebugControl(SysDbgReadMsr).

16 Oct 2008, 18:25

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17663
Location: In your JS exploiting you and your system

revolution

IceStudent wrote:

Why not to use the MSR registers for it?

The reason is that any processor with test registers does not also have MSRs. I don't recall the exact change over point but the 80386 has test registers and the Pentium (and up) have MSRs. Somewhere in between the two the TRs were replaced with MSRs and they never existed together in the same CPU.

16 Oct 2008, 23:31

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