linux-kernel - Re: [PATCH] objtool,x86: Verify poke_int3

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Message-ID: <20200728083429.GP119549@hirez.programming.kicks-ass.net>
Date:   Tue, 28 Jul 2020 10:34:29 +0200
From:   peterz@...radead.org
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, mbenes@...e.cz
Subject: Re: [PATCH] objtool,x86: Verify poke_int3_handler() is self contained

On Mon, Jul 27, 2020 at 10:56:03PM +0200, Thomas Gleixner wrote:
> peterz@...radead.org writes:
> > Abuse the SMAP rules to ensure poke_int3_handler() doesn't call out to
> > anything.
> 
> Yuck. Isn't that what noinstr is for or am I missing something?

Well, we don't want poke_int3_handler() to call out to noinstr either.

So noinstr only allows calling noinstr, The above hack only allows it
calling uaccess-safe functions, and the group of functions that is both
noinstr and uaccess-safe is 'small'.

But like I said yesterday, perhaps this wants it own annotation. Then we
can also verify the lack of any dynamic code.

So yes, yuck and a bad idea, ignore this ;-)