Re: [PATCH v2] x86/mm: warn on W+x mappings

From: Ingo Molnar <mingo@kernel.org>
To: Stephen Smalley <sds@tycho.nsa.gov>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	keescook@chromium.org, Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Brian Gerst <brgerst@gmail.com>
Subject: Re: [PATCH v2] x86/mm: warn on W+x mappings
Date: Tue, 6 Oct 2015 09:32:05 +0200	[thread overview]
Message-ID: <20151006073205.GA11115@gmail.com> (raw)
In-Reply-To: <5612CBE8.2010504@tycho.nsa.gov>

* Stephen Smalley <sds@tycho.nsa.gov> wrote:

> On 10/03/2015 07:27 AM, Ingo Molnar wrote:
> > 
> > * Stephen Smalley <sds@tycho.nsa.gov> wrote:
> > 
> >> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> >> index 30564e2..f8b1573 100644
> >> --- a/arch/x86/mm/init_64.c
> >> +++ b/arch/x86/mm/init_64.c
> >> @@ -1150,6 +1150,8 @@ void mark_rodata_ro(void)
> >>  	free_init_pages("unused kernel",
> >>  			(unsigned long) __va(__pa_symbol(rodata_end)),
> >>  			(unsigned long) __va(__pa_symbol(_sdata)));
> >> +
> >> +	debug_checkwx();
> > 
> > Any reason to not do this on NX capable 32-bit kernels as well?
> 
> Done in v3.  However, I do see lots of W+X mappings there.

Ha! That's a debug check plan gone very well! :)

> [    1.012796] WARNING: CPU: 1 PID: 1 at arch/x86/mm/dump_pagetables.c:225 note_page+0x65d/0x840()
> [    1.012803] x86/mm: Found insecure W+X mapping at address f4a00000/0xf4a00000

What does this range correspond to on your kernel?

Thanks,

	Ingo