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Re: [PATCH v8 12/28] x86/insn-eval: Add utility functions to get segment selector

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On Tue, Sep 26, 2017 at 09:21:44PM -0700, Ricardo Neri wrote:
> This is true except when we don't have an insn at all (well, it may be
> non-NULL but it will only contain garbage). The case to which I am
> referring is when we begin decoding our instruction. The first step is
> to copy_from_user the instruction and populate insn. For this we must
> calculate the linear address from where we copy using CS and rIP.

Where do we do that?

> Furthermore, in this only case we don't need to look at insn at all as
> the only register involved is rIP no segment override prefixes are
> allowed.

In any case, as it is now it sounds convoluted: you may or may not
have an insn, and yet you call get_overridden_seg_reg() on it but you
don't really need segment overrides because you only need CS and rIP
initially.

Sounds to me like this initial parsing should be done separately from
this function...

> I only used "(E)" (i.e., not the "(R|)" part) as these utility
> functions will deal mostly with protected mode, unless FS or GS are
> used in long mode.

eIP or rIP is simply much easier to type and parse. Those brackets, not
really.

> I only check for a NULL insn when needed (i.e., the contents of the
> instruction could change the used segment register).

... and those if (!insn) tests sprinkled around simply make the code
unreadable and if we can get rid of them, we should.

-- 
Regards/Gruss,
    Boris.

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

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Re: [PATCH v8 12/28] x86/insn-eval: Add utility functions to get  segment selector Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-09-27 06:30 +0200
  Re: [PATCH v8 12/28] x86/insn-eval: Add utility functions to get  segment selector Borislav Petkov <bp@suse.de> - 2017-09-27 13:50 +0200
    Re: [PATCH v8 12/28] x86/insn-eval: Add utility functions to get  segment selector Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-09-28 00:40 +0200
      Re: [PATCH v8 12/28] x86/insn-eval: Add utility functions to get  segment selector Borislav Petkov <bp@suse.de> - 2017-09-28 11:40 +0200
        Re: [PATCH v8 12/28] x86/insn-eval: Add utility functions to get  segment selector Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-09-29 08:10 +0200
          Re: [PATCH v8 12/28] x86/insn-eval: Add utility functions to get  segment selector Borislav Petkov <bp@suse.de> - 2017-09-29 14:00 +0200

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