From: Serge Semin <fancer.lancer@gmail.com>
To: Matt Redfearn <matt.redfearn@mips.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
ralf@linux-mips.org, miodrag.dinic@mips.com, jhogan@kernel.org,
goran.ferenc@mips.com, david.daney@cavium.com,
paul.gortmaker@windriver.com, paul.burton@mips.com,
alex.belits@cavium.com, Steven.Hill@cavium.com,
alexander.sverdlin@nokia.com, kumba@gentoo.org,
marcin.nowakowski@mips.com, James.hogan@mips.com,
Peter.Wotton@mips.com, Sergey.Semin@t-platforms.ru,
linux-mips@linux-mips.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 11/14] MIPS: memblock: Print out kernel virtual mem layout
Date: Wed, 24 Jan 2018 13:08:31 +0300 [thread overview]
Message-ID: <20180124100831.GB2281@mobilestation> (raw)
In-Reply-To: <e751ccda-ab57-dfe8-0a16-25bb5368337c@mips.com>
Hello Matt,
On Wed, Jan 24, 2018 at 09:46:07AM +0000, Matt Redfearn <matt.redfearn@mips.com> wrote:
> Hi Serge,
>
> On 23/01/18 19:10, Serge Semin wrote:
> >Hello Matt,
> >
> >On Tue, Jan 23, 2018 at 03:35:14PM +0000, Matt Redfearn <matt.redfearn@mips.com> wrote:
> >>Hi Serge,
> >>
> >>On 19/01/18 14:27, Serge Semin wrote:
> >>>On Fri, Jan 19, 2018 at 07:59:43AM +0000, Matt Redfearn <matt.redfearn@mips.com> wrote:
> >>>
> >>>Hello Matt,
> >>>
> >>>>Hi Serge,
> >>>>
> >>>>
> >>>>
> >>>>On 18/01/18 20:18, Serge Semin wrote:
> >>>>>On Thu, Jan 18, 2018 at 12:03:03PM -0800, Florian Fainelli <f.fainelli@gmail.com> wrote:
> >>>>>>On 01/17/2018 02:23 PM, Serge Semin wrote:
> >>>>>>>It is useful to have the kernel virtual memory layout printed
> >>>>>>>at boot time so to have the full information about the booted
> >>>>>>>kernel. In some cases it might be unsafe to have virtual
> >>>>>>>addresses freely visible in logs, so the %pK format is used if
> >>>>>>>one want to hide them.
> >>>>>>>
> >>>>>>>Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
> >>>>>>
> >>>>>>I personally like having that information because that helps debug and
> >>>>>>have a quick reference, but there appears to be a trend to remove this
> >>>>>>in the name of security:
> >>>>>>
> >>>>>>https://patchwork.kernel.org/patch/10124007/
> >>>>>>
> >>>>>>maybe hide this behind a configuration option?
> >>>>>
> >>>>>Yeah, arm code was the place I picked the function up.) But in my case
> >>>>>I've used %pK so the pointers would disappear from logging when
> >>>>>kptr_restrict sysctl is 1 or 2.
> >>>>>I agree, that we might need to make the printouts optional. If there is
> >>>>>any kernel config, which for instance increases the kernel security we
> >>>>>could also use it or anything else to discard the printouts at compile
> >>>>>time.
> >>>>
> >>>>
> >>>>Certainly, when KASLR is active it would be preferable to hide this
> >>>>information, so you could use CONFIG_RELOCATABLE. The existing KASLR stuff
> >>>>additionally hides this kind of information behind CONFIG_DEBUG_KERNEL, so
> >>>>that only people actively debugging the kernel see it:
> >>>>
> >>>>http://elixir.free-electrons.com/linux/v4.15-rc8/source/arch/mips/kernel/setup.c#L604
> >>>
> >>>Ok. I'll hide the printouts behind both of that config macros in the next patchset
> >>>version.
> >>
> >>
> >>Another thing to note - since ad67b74d2469d ("printk: hash addresses printed
> >>with %p") %pK at this time in the boot process is useless since the RNG is
> >>not sufficiently initialised and all prints end up being "(ptrval)". Hence
> >>after v4.15-rc2 we end up with output like:
> >>
> >>[ 0.000000] Kernel virtual memory layout:
> >>[ 0.000000] lowmem : 0x(ptrval) - 0x(ptrval) ( 256 MB)
> >>[ 0.000000] .text : 0x(ptrval) - 0x(ptrval) (7374 kB)
> >>[ 0.000000] .data : 0x(ptrval) - 0x(ptrval) (1901 kB)
> >>[ 0.000000] .init : 0x(ptrval) - 0x(ptrval) (1600 kB)
> >>[ 0.000000] .bss : 0x(ptrval) - 0x(ptrval) ( 415 kB)
> >>[ 0.000000] vmalloc : 0x(ptrval) - 0x(ptrval) (1023 MB)
> >>[ 0.000000] fixmap : 0x(ptrval) - 0x(ptrval) ( 68 kB)
> >>
> >
> >It must be some bug in the algo. What point in the %pK then? According to
> >the documentation the only way to see the pointers is when (kptr_restrict == 0).
> >But if it is we don't get into the restricted_pointer() method at all:
> >http://elixir.free-electrons.com/linux/v4.15-rc9/source/lib/vsprintf.c#L1934
> >In this case the vsprintf() executes the method ptr_to_id(), which of course
> >default to _not_ leak addresses, and hash it before printing.
> >
> >Really %pK isn't supposed to be dependent from RNG at all since kptr_restrict
> >doesn't do any value randomization.
>
>
> That was true until v4.15-rc2. The behavior of %pK was changed without that
> being reflected in the documentation. A patch
> (https://patchwork.kernel.org/patch/10124413/) is in progress to update
> this.
>
> >
> >>
> >>The %px format specifier was added for cases such as this, where we really
> >>want to print the unmodified address. And as long as this function is
> >>suitably guarded to only do this when KASLR is deactivated /
> >>CONFIG_DEBUG_KERNEL is activated, etc, then we are not unwittingly leaking
> >>information - we are deliberately making it available.
> >>
> >
> >If %pK would work as it's stated by the kernel documentation:
> >https://www.kernel.org/doc/Documentation/printk-formats.txt
> >then the only change I'd suggest to have here is to close the kernel memory
> >layout printout method by the CONFIG_DEBUG_KERNEL ifdef-macro. The kptr_restrict
> >should default to 1/2 if the KASLR is activated:
> >https://lwn.net/Articles/444556/
>
> Yeah, again, the documentation is no longer correct, and %pK will always be
> hashed, and before the RNG is initialized it does not even hash it, just
> returning "(ptrval)". So I'd recommend guarding with CONFIG_DEBUG_KERNEL
> and switching the format specifier to %px.
>
Oh, it isn't the bug then) I'll do as you suggest and replace %pK with
%px closing the code by CONFIG_DEBUG_KERNEL macro.
Regards,
-Sergey
> Thanks,
> Matt
>
> >
> >Regards,
> >-Sergey
> >
> >>Thanks,
> >>Matt
> >>
> >>>
> >>>Regards,
> >>>-Sergey
> >>>
> >>>>
> >>>>Thanks,
> >>>>Matt
> >>>>
> >>>>>
> >>>>>>--
> >>>>>>Florian
next prev parent reply other threads:[~2018-01-24 10:08 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-17 22:22 [PATCH 00/14] MIPS: memblock: Switch arch code to NO_BOOTMEM Serge Semin
2018-01-17 22:22 ` [PATCH 01/14] MIPS: memblock: Add RESERVED_NOMAP memory flag Serge Semin
2018-01-17 22:23 ` [PATCH 02/14] MIPS: memblock: Surely map BSS kernel memory section Serge Semin
2018-01-22 16:35 ` Matt Redfearn
2018-01-22 21:47 ` Serge Semin
2018-01-23 11:03 ` Matt Redfearn
2018-01-23 19:27 ` Serge Semin
2018-01-24 9:49 ` Matt Redfearn
2018-01-24 10:03 ` Serge Semin
2018-01-17 22:23 ` [PATCH 03/14] MIPS: memblock: Reserve initrd memory in memblock Serge Semin
2018-01-17 22:23 ` [PATCH 04/14] MIPS: memblock: Discard bootmem initialization Serge Semin
2018-01-17 22:23 ` [PATCH 05/14] MIPS: memblock: Add reserved memory regions to memblock Serge Semin
2018-01-17 22:23 ` [PATCH 06/14] MIPS: memblock: Reserve kdump/crash regions in memblock Serge Semin
2018-01-17 22:23 ` [PATCH 07/14] MIPS: memblock: Mark present sparsemem sections Serge Semin
2018-01-24 6:13 ` Marcin Nowakowski
2018-01-24 7:27 ` Serge Semin
2018-01-17 22:23 ` [PATCH 08/14] MIPS: memblock: Simplify DMA contiguous reservation Serge Semin
2018-01-17 22:23 ` [PATCH 09/14] MIPS: memblock: Allow memblock regions resize Serge Semin
2018-01-17 22:23 ` [PATCH 10/14] MIPS: memblock: Perform early low memory test Serge Semin
2018-01-17 22:23 ` [PATCH 11/14] MIPS: memblock: Print out kernel virtual mem layout Serge Semin
2018-01-18 20:03 ` Florian Fainelli
2018-01-18 20:18 ` Serge Semin
2018-01-19 7:59 ` Matt Redfearn
2018-01-19 14:27 ` Serge Semin
2018-01-23 15:35 ` Matt Redfearn
2018-01-23 19:10 ` Serge Semin
2018-01-24 9:46 ` Matt Redfearn
2018-01-24 10:08 ` Serge Semin [this message]
2018-01-17 22:23 ` [PATCH 12/14] MIPS: memblock: Discard bootmem from Loongson3 code Serge Semin
2018-01-23 22:28 ` Jiaxun Yang
2018-01-23 19:36 ` Serge Semin
2018-01-17 22:23 ` [PATCH 13/14] MIPS: memblock: Discard bootmem from SGI IP27 code Serge Semin
2018-01-17 22:23 ` [PATCH 14/14] MIPS: memblock: Deactivate bootmem allocator Serge Semin
2018-01-23 23:59 ` James Hogan
2018-01-24 8:28 ` Serge Semin
2018-01-22 16:36 ` [PATCH 00/14] MIPS: memblock: Switch arch code to NO_BOOTMEM Matt Redfearn
2018-01-22 21:33 ` Serge Semin
2018-01-23 11:29 ` Mathieu Malaterre
2018-01-23 14:01 ` Matt Redfearn
2018-01-25 17:58 ` Alexander Sverdlin
2018-01-25 20:17 ` Serge Semin
2018-01-31 0:21 ` Serge Semin
2018-02-02 3:54 ` [PATCH v2 00/15] " Serge Semin
2018-02-02 3:54 ` [PATCH v2 01/15] MIPS: memblock: Add RESERVED_NOMAP memory flag Serge Semin
2018-02-13 11:21 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 02/15] MIPS: memblock: Surely map BSS kernel memory section Serge Semin
2018-02-13 11:22 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 03/15] MIPS: memblock: Reserve initrd memory in memblock Serge Semin
2018-02-13 11:22 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 04/15] MIPS: memblock: Discard bootmem initialization Serge Semin
2018-02-13 11:28 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 05/15] MIPS: KASLR: Drop relocatable fixup from reservation_init Serge Semin
2018-02-13 11:30 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 06/15] MIPS: memblock: Add reserved memory regions to memblock Serge Semin
2018-02-13 13:44 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 07/15] MIPS: memblock: Reserve kdump/crash regions in memblock Serge Semin
2018-02-13 13:45 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 08/15] MIPS: memblock: Mark present sparsemem sections Serge Semin
2018-02-13 13:50 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 09/15] MIPS: memblock: Simplify DMA contiguous reservation Serge Semin
2018-02-13 13:51 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 10/15] MIPS: memblock: Allow memblock regions resize Serge Semin
2018-02-13 13:55 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 11/15] MIPS: memblock: Perform early low memory test Serge Semin
2018-02-13 14:01 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 12/15] MIPS: memblock: Print out kernel virtual mem layout Serge Semin
2018-02-13 14:05 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 13/15] MIPS: memblock: Discard bootmem from Loongson3 code Serge Semin
2018-02-13 14:09 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 14/15] MIPS: memblock: Discard bootmem from SGI IP27 code Serge Semin
2018-02-13 14:17 ` Matt Redfearn
2018-02-02 3:54 ` [PATCH v2 15/15] MIPS: memblock: Deactivate bootmem allocator Serge Semin
2018-02-13 14:18 ` Matt Redfearn
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