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Re: [v6 PATCH 08/21] x86/insn-eval: Add utility function to get segment descriptor base address

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  Re: [v6 PATCH 08/21] x86/insn-eval: Add utility function to get  segment descriptor base address Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-04-27 01:00 +0200
    Re: [v6 PATCH 08/21] x86/insn-eval: Add utility function to get  segment descriptor base address Borislav Petkov <bp@suse.de> - 2017-05-05 19:40 +0200

#1631783 — Re: [v6 PATCH 08/21] x86/insn-eval: Add utility function to get segment descriptor base address

On Thu, 2017-04-20 at 10:25 +0200, Borislav Petkov wrote:
> > + * insn_get_seg_base() - Obtain base address contained in
> descriptor
> > + * @regs:    Set of registers containing the segment selector
> > + * @insn:    Instruction structure with selector override prefixes
> > + * @regoff:  Operand offset, in pt_regs, of which the selector is
> needed
> > + * @use_default_seg: Use the default segment instead of prefix
> overrides
> 
> I'm wondering whether you really need that bool or you can deduce this
> from pt_regs... I guess I'll see...

Probably insn_get_seg_base() itself can verify if there are segment
override prefixes in the struct insn. If yes, use them except for
specific cases such as CS.

On an unrelated note, I still have the problem of using DS vs ES for
string instructions. Perhaps instead of a use_default_seg flag, a
string_instruction flag that indicates how to determine the default
segment.

Thanks and BR,
Ricardo

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#1636512

On Wed, Apr 26, 2017 at 03:52:41PM -0700, Ricardo Neri wrote:
> Probably insn_get_seg_base() itself can verify if there are segment
> override prefixes in the struct insn. If yes, use them except for
> specific cases such as CS.

... and depending on whether in long mode or not.

> On an unrelated note, I still have the problem of using DS vs ES for
> string instructions. Perhaps instead of a use_default_seg flag, a
> string_instruction flag that indicates how to determine the default
> segment.

... or you can look at the insn opcode directly. AFAICT, you need
to check whether the opcode is 0xa4 or 0xa5 and that the insn is a
single-byte opcode, i.e., not from the secondary map escaped with 0xf or
some of the other multi-byte opcode maps.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

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