linux-kernel - Re: [PATCH v2] x86/dumpstack: Fix misleading instruction pointer error message

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Message-ID: <20201103182018.GE4111@zn.tnic>
Date:   Tue, 3 Nov 2020 19:20:18 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Mark Mossberg <mark.mossberg@...il.com>, tglx@...utronix.de,
        mingo@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org,
        hpa@...or.com, jannh@...gle.com, kyin@...hat.com
Subject: Re: [PATCH v2] x86/dumpstack: Fix misleading instruction pointer
 error message

On Tue, Nov 03, 2020 at 07:11:15PM +0100, Oleg Nesterov wrote:
> > I'm thinking copy_code() should not use copy_from_user_nmi() if former
> > can be called in non-atomic context too.
> 
> I understand, but why do you think this makes sense?

Because the copy_from_user_nmi()'s name tells me that it is at least
supposed to be called in atomic context. At least this is how I
understand it. And in atomic context regs is supposed to belong to
current, right?

So I kinda agree with what you're proposing but if copy_from_user_nmi()
can be "tricked" into reading off from the weeds, then there should be
a big fat warning above it at least so that users are warned to do the
appropriate checks.

Or there should be another wrapper around it which does the
regs-belongs-to-current checks, etc and copy_code() should use that
wrapper...

AFAICT at least.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette