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From: Andrew Morton <akpm@linux-foundation.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: dan.carpenter@oracle.com, will@kernel.org, ebiederm@xmission.com,
	linux-arch@vger.kernel.org, security@kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] execve: warn if process starts with executable stack
Date: Tue, 10 Dec 2019 17:47:26 -0800	[thread overview]
Message-ID: <20191210174726.101e434df59b6aec8a53cca1@linux-foundation.org> (raw)
In-Reply-To: <20191208171918.GC19716@avx2>

On Sun, 8 Dec 2019 20:19:18 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:

> There were few episodes of silent downgrade to an executable stack over
> years:
> 
> 1) linking innocent looking assembly file will silently add executable
>    stack if proper linker options is not given as well:
> 
> 	$ cat f.S
> 	.intel_syntax noprefix
> 	.text
> 	.globl f
> 	f:
> 	        ret
> 
> 	$ cat main.c
> 	void f(void);
> 	int main(void)
> 	{
> 	        f();
> 	        return 0;
> 	}
> 
> 	$ gcc main.c f.S
> 	$ readelf -l ./a.out
> 	  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
>                          0x0000000000000000 0x0000000000000000  RWE    0x10
> 			 					 ^^^
> 
> 2) converting C99 nested function into a closure
> https://nullprogram.com/blog/2019/11/15/
> 
> 	void intsort2(int *base, size_t nmemb, _Bool invert)
> 	{
> 	    int cmp(const void *a, const void *b)
> 	    {
> 	        int r = *(int *)a - *(int *)b;
> 	        return invert ? -r : r;
> 	    }
> 	    qsort(base, nmemb, sizeof(*base), cmp);
> 	}
> 
> will silently require stack trampolines while non-closure version will not.
> 
> Without doubt this behaviour is documented somewhere, add a warning so that
> developers and users can at least notice. After so many years of x86_64 having
> proper executable stack support it should not cause too many problems.

hm, OK, let's give it a trial run.

> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -761,6 +761,11 @@ int setup_arg_pages(struct linux_binprm *bprm,
>  		goto out_unlock;
>  	BUG_ON(prev != vma);
>  
> +	if (unlikely(vm_flags & VM_EXEC)) {
> +		pr_warn_once("process '%pD4' started with executable stack\n",
> +			     bprm->file);
> +	}
> +
>  	/* Move stack pages down in memory. */
>  	if (stack_shift) {
>  		ret = shift_arg_pages(vma, stack_shift);

What are poor users supposed to do if this message comes out? 
Hopefully google the message and end up at this thread.  What do you
want to tell them?


  reply	other threads:[~2019-12-11  1:47 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-08 17:19 Alexey Dobriyan
2019-12-11  1:47 ` Andrew Morton [this message]
2019-12-11  7:22   ` Alexey Dobriyan
2019-12-11  9:59     ` Willy Tarreau
2019-12-11 18:19       ` Alexey Dobriyan
2019-12-11 18:24         ` Willy Tarreau
2019-12-12 21:25           ` Alexey Dobriyan
2019-12-13  9:56             ` Dan Carpenter
2019-12-13 10:23               ` Willy Tarreau
2020-02-25 21:52   ` Kees Cook

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