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From: Alexey Dobriyan <adobriyan@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	security@kernel.org, ben.dooks@codethink.co.uk
Subject: Re: [PATCH] ELF: warn if process starts with executable stack
Date: Tue, 19 Nov 2019 00:36:03 +0300	[thread overview]
Message-ID: <20191118213603.GA24086@avx2> (raw)
In-Reply-To: <20191118125457.778e44dfd4740d24795484c7@linux-foundation.org>

On Mon, Nov 18, 2019 at 12:54:57PM -0800, Andrew Morton wrote:
> On Mon, 18 Nov 2019 17:51:15 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> 
> > PT_GNU_STACK is fail open design,
> 
> Not sure what this means.  Please expand on the motivation for this
> change.
> 
> > at least warn people that something
> > isn't right.
> 
> People who use an executable stack get a kernel splat.  How is that
> useful?

There were two stories about silent downgrade to an executable stack:

1)
compiling .S file and linking it to normal code:

	$ cat f.S
	.intel_syntax noprefix
	.text
	.globl f
	f:
	        ret

will silently add PT_GNU_STACK segment with RWE permissions

2)
closures with nested functions will require executable stack
https://nullprogram.com/blog/2019/11/15/

> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -762,6 +762,13 @@ int setup_arg_pages(struct linux_binprm *bprm,
> >  		goto out_unlock;
> >  	BUG_ON(prev != vma);
> >  
> > +#ifdef CONFIG_MMU

This code is already under CONFIG_MMU. I'll resend.

  reply	other threads:[~2019-11-18 21:36 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-18 14:51 Alexey Dobriyan
2019-11-18 17:13 ` Ben Dooks
2019-11-18 20:54 ` Andrew Morton
2019-11-18 21:36   ` Alexey Dobriyan [this message]
2019-11-18 21:52   ` [PATCH] exec: " Alexey Dobriyan
2019-11-19  5:32     ` Dan Carpenter
2019-11-20 19:17     ` Will Deacon
2019-11-20 20:28       ` Eric W. Biederman
2019-11-21  9:38         ` Will Deacon
2019-12-08 16:43           ` Alexey Dobriyan

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