linux-kernel - Re: [RFC PATCH v2 1/2] Randomization of address chosen by mmap.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 22 Mar 2018 13:53:14 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Ilya Smith <blackzert@...il.com>
Cc:     rth@...ddle.net, ink@...assic.park.msu.ru, mattst88@...il.com,
        vgupta@...opsys.com, linux@...linux.org.uk, tony.luck@...el.com,
        fenghua.yu@...el.com, jhogan@...nel.org, ralf@...ux-mips.org,
        jejb@...isc-linux.org, deller@....de, benh@...nel.crashing.org,
        paulus@...ba.org, mpe@...erman.id.au, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, ysato@...rs.sourceforge.jp,
        dalias@...c.org, davem@...emloft.net, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        nyc@...omorphy.com, viro@...iv.linux.org.uk, arnd@...db.de,
        gregkh@...uxfoundation.org, deepa.kernel@...il.com,
        mhocko@...e.com, hughd@...gle.com, kstewart@...uxfoundation.org,
        pombredanne@...b.com, steve.capper@....com, punit.agrawal@....com,
        paul.burton@...s.com, aneesh.kumar@...ux.vnet.ibm.com,
        npiggin@...il.com, keescook@...omium.org, bhsharma@...hat.com,
        riel@...hat.com, nitin.m.gupta@...cle.com,
        kirill.shutemov@...ux.intel.com, dan.j.williams@...el.com,
        jack@...e.cz, ross.zwisler@...ux.intel.com, jglisse@...hat.com,
        willy@...radead.org, aarcange@...hat.com, oleg@...hat.com,
        linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-metag@...r.kernel.org, linux-mips@...ux-mips.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v2 1/2] Randomization of address chosen by mmap.

On Thu, 22 Mar 2018 19:36:37 +0300 Ilya Smith <blackzert@...il.com> wrote:

>  include/linux/mm.h |  16 ++++--
>  mm/mmap.c          | 164 +++++++++++++++++++++++++++++++++++++++++++++++++++++

You'll be wanting to update the documentation. 
Documentation/sysctl/kernel.txt and
Documentation/admin-guide/kernel-parameters.txt.

> ...
>
> @@ -2268,6 +2276,9 @@ extern unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info);
>  static inline unsigned long
>  vm_unmapped_area(struct vm_unmapped_area_info *info)
>  {
> +	/* How about 32 bit process?? */
> +	if ((current->flags & PF_RANDOMIZE) && randomize_va_space > 3)
> +		return unmapped_area_random(info);

The handling of randomize_va_space is peculiar.  Rather than being a
bitfield which independently selects different modes, it is treated as
a scalar: the larger the value, the more stuff we randomize.

I can see the sense in that (and I wonder what randomize_va_space=5
will do).  But it is...  odd.

Why did you select randomize_va_space=4 for this?  Is there a mode 3
already and we forgot to document it?  Or did you leave a gap for
something?  If the former, please feel free to fix the documentation
(in a separate, preceding patch) while you're in there ;)

>  	if (info->flags & VM_UNMAPPED_AREA_TOPDOWN)
>  		return unmapped_area_topdown(info);
>  	else
> @@ -2529,11 +2540,6 @@ int drop_caches_sysctl_handler(struct ctl_table *, int,
>  void drop_slab(void);
>  void drop_slab_node(int nid);
>  
>
> ...
>
> @@ -1780,6 +1781,169 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>  	return error;
>  }
>  
> +unsigned long unmapped_area_random(struct vm_unmapped_area_info *info)
> +{

This function is just dead code if CONFIG_MMU=n, yes?  Let's add the
ifdefs to make it go away in that case.

> +	struct mm_struct *mm = current->mm;
> +	struct vm_area_struct *vma = NULL;
> +	struct vm_area_struct *visited_vma = NULL;
> +	unsigned long entropy[2];
> +	unsigned long length, low_limit, high_limit, gap_start, gap_end;
> +	unsigned long addr = 0;
> +
> +	/* get entropy with prng */
> +	prandom_bytes(&entropy, sizeof(entropy));
> +	/* small hack to prevent EPERM result */
> +	info->low_limit = max(info->low_limit, mmap_min_addr);
> +
>
> ...
>
> +found:
> +	/* We found a suitable gap. Clip it with the original high_limit. */
> +	if (gap_end > info->high_limit)
> +		gap_end = info->high_limit;
> +	gap_end -= info->length;
> +	gap_end -= (gap_end - info->align_offset) & info->align_mask;
> +	/* only one suitable page */
> +	if (gap_end ==  gap_start)
> +		return gap_start;
> +	addr = entropy[1] % (min((gap_end - gap_start) >> PAGE_SHIFT,
> +							 0x10000UL));

What does the magic 10000 mean?  Isn't a comment needed explaining this?

> +	addr = gap_end - (addr << PAGE_SHIFT);
> +	addr += (info->align_offset - addr) & info->align_mask;
> +	return addr;
> +}
>
> ...
>