[SATLUG] New kernel security problem

[Paul S. Bains]

What you are saying makes sense. Overwriting or erasing register
contents or areas of RAM that are in use is generally a bad thing...!

On Sun, 13 Jun 2004 18:06:53 -0500
"K. Spoon" <kell at spoonix.com> wrote:

> I found this via google:
> 
>   FSAVE saves the entire floating-point unit state, including all the
>   information saved by FSTENV plus the contents of all the registers,
>   to a 94 or 108 byte area of memory (depending on the CPU mode). 
>   FRSTOR restores the floating-point state from the same area of
>   memory.
> 
> I'm guessing that the first call to FSAVE ensures that junk gets
> written to the space that should be used for holding information from
> the registers, and then when you call FRSTOR it wipes out useful
> registers (like the one that tracks where the CPU is in executing
> stuff on the stack :) with the garbage it just "saved".
> 
> I'm no asm monkey, though, and I don't know much about x86 arch.
> 
> 
> -- 
> K. Spoon <kell at spoonix.com>
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