linux-kernel - Re: [PATCH 8/9] x86/dumpstack: Save first regs set for the executive summary

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Date:   Fri, 16 Mar 2018 13:38:35 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        X86 ML <x86@...nel.org>, Andy Lutomirski <luto@...capital.net>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 8/9] x86/dumpstack: Save first regs set for the executive
 summary

On Fri, Mar 16, 2018 at 06:45:29PM +0100, Borislav Petkov wrote:
> > You're better off getting rid of the CR2 line from __show_regs(),
> > because it can be dangerously confusing. It's not actually part of the
> > saved register state at all, it's something entirely different. It's
> > like showing the current eflags rather than the eflags saved on the
> > faulting stack.
> 
> Yeah, __show_regs() goes and gets a bunch of registers at the time
> __show_regs() runs. Which is ok for those which don't change in between
> but CR2 is special.
> 
> We probably could improve that situation by having a struct fault_regs
> or so wrapping pt_regs and adding a bunch of fields like CR2 etc. Fault
> handlers would then populate fault_regs at fault time while we're atomic
> and then hand this struct down to the printing path.
> 
> The printing path would fill out the rest and this way we won't have any
> of that monkey business anymore.
> 
> Thoughts?

It would be nice if we could save *all* the printed registers before
they get a chance to change, but I don't know how feasible that is.
Some of the registers change in entry code, like CR3 and GS.

-- 
Josh