Messages in this thread |  | | Date | Wed, 27 Sep 2017 13:47:13 +0200 | From | Borislav Petkov <> | Subject | 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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