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From: Peter Zijlstra <peterz@infradead.org>
To: Jessica Yu <jeyu@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	keescook@chromium.org
Subject: Re: [PATCH] module: Harden STRICT_MODULE_RWX
Date: Mon, 6 Apr 2020 13:27:32 +0200	[thread overview]
Message-ID: <20200406112732.GK20730@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200406104615.GA9629@linux-8ccs>

On Mon, Apr 06, 2020 at 12:46:17PM +0200, Jessica Yu wrote:
> +++ Miroslav Benes [06/04/20 11:55 +0200]:
> > On Fri, 3 Apr 2020, Josh Poimboeuf wrote:
> > 
> > > On Fri, Apr 03, 2020 at 06:37:16PM +0200, Peter Zijlstra wrote:
> > > > +{
> > > > +	int i;
> > > > +
> > > > +	for (i = 0; i < hdr->e_shnum; i++) {
> > > > +		if (sechdrs[i].sh_flags & (SHF_EXECINSTR|SHF_WRITE))
> > > > +			return -ENOEXEC;
> > > 
> > > I think you only want the error when both are set?
> > > 
> > > 		if (sechdrs[i].sh_flags & (SHF_EXECINSTR|SHF_WRITE) == (SHF_EXECINSTR|SHF_WRITE))
> > 
> > A section with SHF_EXECINSTR and SHF_WRITE but without SHF_ALLOC would be
> > strange though, no? It wouldn't be copied to the final module later
> > anyway.
> 
> That's right - move_module() ignores !SHF_ALLOC sections and does not
> copy them over to their final location. So I think we want to look for
> SHF_EXECINSTR|SHF_WRITE|SHF_ALLOC here..

So I did notice that !SHF_ALLOC sections get ignored, but since this
check is about W^X we don't strictly care about SHF_ALLOC. What we care
about it never allowing a writable and executable map.

Adding ALLOC to the test only allows for future mistakes and doesn't
make the check any better.


  reply	other threads:[~2020-04-06 11:27 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-03 16:37 [PATCH] module: Harden STRICT_MODULE_RWX Peter Zijlstra
2020-04-03 16:56 ` Josh Poimboeuf
2020-04-03 17:08   ` Peter Zijlstra
2020-04-06  9:55   ` Miroslav Benes
2020-04-06 10:46     ` Jessica Yu
2020-04-06 11:27       ` Peter Zijlstra [this message]
2020-04-06 12:53         ` Jessica Yu
2020-04-06 14:11           ` Peter Zijlstra
2020-04-07  7:43         ` Miroslav Benes
2020-04-09 16:55           ` Miroslav Benes
2020-04-10  9:04             ` Jessica Yu
2020-04-03 16:59 ` Josh Poimboeuf

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