From: Andrew Morton <akpm@linux-foundation.org>
To: Ilya Smith <blackzert@gmail.com>
Cc: rth@twiddle.net, ink@jurassic.park.msu.ru, mattst88@gmail.com,
vgupta@synopsys.com, linux@armlinux.org.uk, tony.luck@intel.com,
fenghua.yu@intel.com, jhogan@kernel.org, ralf@linux-mips.org,
jejb@parisc-linux.org, deller@gmx.de, benh@kernel.crashing.org,
paulus@samba.org, mpe@ellerman.id.au, schwidefsky@de.ibm.com,
heiko.carstens@de.ibm.com, ysato@users.sourceforge.jp,
dalias@libc.org, davem@davemloft.net, tglx@linutronix.de,
mingo@redhat.com, hpa@zytor.com, x86@kernel.org,
nyc@holomorphy.com, viro@zeniv.linux.org.uk, arnd@arndb.de,
gregkh@linuxfoundation.org, deepa.kernel@gmail.com,
mhocko@suse.com, hughd@google.com, kstewart@linuxfoundation.org,
pombredanne@nexb.com, steve.capper@arm.com,
punit.agrawal@arm.com, paul.burton@mips.com,
aneesh.kumar@linux.vnet.ibm.com, npiggin@gmail.c
Subject: Re: [RFC PATCH v2 1/2] Randomization of address chosen by mmap.
Date: Thu, 22 Mar 2018 13:53:14 -0700 [thread overview]
Message-ID: <20180322135314.61efce938293e051e118fa46@linux-foundation.org> (raw)
In-Reply-To: <1521736598-12812-2-git-send-email-blackzert@gmail.com>
On Thu, 22 Mar 2018 19:36:37 +0300 Ilya Smith <blackzert@gmail.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;
> +}
>
> ...
>
next parent reply other threads:[~2018-03-22 20:53 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1521736598-12812-1-git-send-email-blackzert@gmail.com>
[not found] ` <1521736598-12812-2-git-send-email-blackzert@gmail.com>
2018-03-22 20:53 ` Andrew Morton [this message]
2018-03-23 17:43 ` [RFC PATCH v2 1/2] Randomization of address chosen by mmap Ilya Smith
[not found] ` <1521736598-12812-3-git-send-email-blackzert@gmail.com>
2018-03-22 20:54 ` [RFC PATCH v2 2/2] Architecture defined limit on memory region random shift Andrew Morton
2018-03-23 17:48 ` Ilya Smith
2018-03-23 17:49 ` Ilya Smith
2018-03-22 20:57 ` [RFC PATCH v2 0/2] Randomization of address chosen by mmap Andrew Morton
2018-03-23 17:25 ` Ilya Smith
2018-03-23 12:48 ` Matthew Wilcox
2018-03-23 17:55 ` Ilya Smith
2018-03-26 8:46 ` Michal Hocko
2018-03-26 19:45 ` Ilya Smith
2018-03-27 7:24 ` Michal Hocko
2018-03-27 13:51 ` Ilya Smith
2018-03-27 14:38 ` Michal Hocko
2018-03-28 18:47 ` Ilya Smith
2018-03-27 22:16 ` Theodore Y. Ts'o
2018-03-28 18:48 ` Ilya Smith
2018-03-27 22:53 ` Kees Cook
2018-03-27 23:49 ` Matthew Wilcox
2018-03-27 23:57 ` Kees Cook
2018-03-28 0:00 ` Rich Felker
2018-03-28 21:07 ` Luck, Tony
2018-04-03 0:11 ` Ilya Smith
2018-03-28 21:07 ` Ilya Smith
2018-03-23 18:00 ` Rich Felker
2018-03-23 19:06 ` Matthew Wilcox
2018-03-23 19:16 ` Rich Felker
2018-03-23 19:29 ` Matthew Wilcox
2018-03-23 19:35 ` Rich Felker
2018-03-28 4:50 ` Rob Landley
2018-03-30 7:55 ` Pavel Machek
2018-03-30 9:07 ` Ilya Smith
2018-03-30 9:57 ` Pavel Machek
2018-03-30 11:10 ` Ilya Smith
2018-03-30 13:33 ` Rich Felker
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