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Message-ID: <20181209214600.GC2217@ZenIV.linux.org.uk>
Date: Sun, 9 Dec 2018 21:46:00 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Tycho Andersen <tycho@...ho.ws>
Cc: linux-sparse@...r.kernel.org, kernel-hardening@...ts.openwall.com,
linux-kernel@...r.kernel.org
Subject: Re: [RFC v1] copy_{to,from}_user(): only inline when !__CHECKER__
On Sun, Dec 09, 2018 at 02:25:23PM -0700, Tycho Andersen wrote:
> > Which sparse checks do not trigger? Explain, please - as it is, I had been
> > unable to guess what could "specifically looks for a call instruction" refer
> > to.
>
> In sparse.c there's check_call_instruction(), which is triggered when
> there's an instruction of OP_CALL type in the basic block. This simply
> compares against the name of the call target to determine whether or
> not to call check_ctu().
Oh, that Linus' experiment with "look for huge constant size argument
to memcpy() et.al."? Frankly, it's not only the wrong place to put the
checks, but breaking inlining loses the _real_ "known constant size"
checks in there.
I don't know if the check_ctu thing has ever caught a bug... What kind of
checks do you want to add? Because this place is almost certainly wrong
for anything useful...
If anything, I would suggest simulating this behaviour with something like
if (__builtin_constant_p(size) && size > something)
/* something that would trigger a warning */
_inside_ copy_from_user()/copy_to_user() and to hell with name-recognizing
magic...
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