From: Jason Yan <yanaijie@huawei.com>
To: Scott Wood <oss@buserror.net>, Daniel Axtens <dja@axtens.net>,
<mpe@ellerman.id.au>, <linuxppc-dev@lists.ozlabs.org>,
<diana.craciun@nxp.com>, <christophe.leroy@c-s.fr>,
<benh@kernel.crashing.org>, <paulus@samba.org>,
<npiggin@gmail.com>, <keescook@chromium.org>,
<kernel-hardening@lists.openwall.com>, <me@tobin.cc>
Cc: <linux-kernel@vger.kernel.org>, <zhaohongjiang@huawei.com>
Subject: Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64
Date: Mon, 2 Mar 2020 10:17:28 +0800 [thread overview]
Message-ID: <35e6c660-3896-bdb8-45f3-c1504aa2171f@huawei.com> (raw)
In-Reply-To: <530c49dfd97c811dc53ffc78c594d7133f7eb1e9.camel@buserror.net>
在 2020/3/1 6:54, Scott Wood 写道:
> On Sat, 2020-02-29 at 15:27 +0800, Jason Yan wrote:
>>
>> 在 2020/2/29 12:28, Scott Wood 写道:
>>> On Fri, 2020-02-28 at 14:47 +0800, Jason Yan wrote:
>>>>
>>>> 在 2020/2/28 13:53, Scott Wood 写道:
>>>>>
>>>>> I don't see any debug setting for %pK (or %p) to always print the
>>>>> actual
>>>>> address (closest is kptr_restrict=1 but that only works in certain
>>>>> contexts)... from looking at the code it seems it hashes even if kaslr
>>>>> is
>>>>> entirely disabled? Or am I missing something?
>>>>>
>>>>
>>>> Yes, %pK (or %p) always hashes whether kaslr is disabled or not. So if
>>>> we want the real value of the address, we cannot use it. But if you only
>>>> want to distinguish if two pointers are the same, it's ok.
>>>
>>> Am I the only one that finds this a bit crazy? If you want to lock a
>>> system
>>> down then fine, but why wage war on debugging even when there's no
>>> randomization going on? Comparing two pointers for equality is not always
>>> adequate.
>>>
>>
>> AFAIK, %p hashing is only exist because of many legacy address printings
>> and force who really want the raw values to switch to %px or even %lx.
>> It's not the opposite of debugging. Raw address printing is not
>> forbidden, only people need to estimate the risk of adrdress leaks.
>
> Yes, but I don't see any format specifier to switch to that will hash in a
> randomized production environment, but not in a debug or other non-randomized
> environment which seems like the ideal default for most debug output.
>
Sorry I have no idea why there is no format specifier considered for
switching of randomized or non-randomized environment. May they think
that raw address should not leak in non-randomized environment too. May
be Kees or Tobin can answer this question.
Kees? Tobin?
>>
>> Turnning to %p may not be a good idea in this situation. So
>> for the REG logs printed when dumping stack, we can disable it when
>> KASLR is open. For the REG logs in other places like show_regs(), only
>> privileged can trigger it, and they are not combind with a symbol, so
>> I think it's ok to keep them.
>>
>> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
>> index fad50db9dcf2..659c51f0739a 100644
>> --- a/arch/powerpc/kernel/process.c
>> +++ b/arch/powerpc/kernel/process.c
>> @@ -2068,7 +2068,10 @@ void show_stack(struct task_struct *tsk, unsigned
>> long *stack)
>> newsp = stack[0];
>> ip = stack[STACK_FRAME_LR_SAVE];
>> if (!firstframe || ip != lr) {
>> - printk("["REG"] ["REG"] %pS", sp, ip, (void *)ip);
>> + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
>> + printk("%pS", (void *)ip);
>> + else
>> + printk("["REG"] ["REG"] %pS", sp, ip,
>> (void *)ip);
>
> This doesn't deal with "nokaslr" on the kernel command line. It also doesn't
> seem like something that every callsite should have to opencode, versus having
> an appropriate format specifier behaves as I described above (and I still
> don't see why that format specifier should not be "%p").
>
Actually I still do not understand why we should print the raw value
here. When KALLSYMS is enabled we have symbol name and offset like
put_cred_rcu+0x108/0x110, and when KALLSYMS is disabled we have the raw
address.
> -Scott
>
>
>
> .
>
next prev parent reply other threads:[~2020-03-02 2:17 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-06 2:58 [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64 Jason Yan
2020-02-06 2:58 ` [PATCH v3 1/6] powerpc/fsl_booke/kaslr: refactor kaslr_legal_offset() and kaslr_early_init() Jason Yan
2020-02-20 13:40 ` Christophe Leroy
2020-02-26 2:11 ` Jason Yan
2020-02-06 2:58 ` [PATCH v3 2/6] powerpc/fsl_booke/64: introduce reloc_kernel_entry() helper Jason Yan
2020-02-20 13:41 ` Christophe Leroy
2020-02-06 2:58 ` [PATCH v3 3/6] powerpc/fsl_booke/64: implement KASLR for fsl_booke64 Jason Yan
2020-02-20 13:48 ` Christophe Leroy
2020-02-26 2:40 ` Jason Yan
2020-02-26 3:33 ` Jason Yan
2020-02-26 5:04 ` [RFC PATCH] Use IS_ENABLED() instead of #ifdefs Christophe Leroy
2020-02-26 6:26 ` Jason Yan
2020-02-26 5:10 ` [PATCH v3 3/6] powerpc/fsl_booke/64: implement KASLR for fsl_booke64 Christophe Leroy
2020-02-26 5:08 ` Christophe Leroy
2020-03-04 21:44 ` Scott Wood
2020-03-05 2:32 ` Jason Yan
2020-02-06 2:58 ` [PATCH v3 4/6] powerpc/fsl_booke/64: do not clear the BSS for the second pass Jason Yan
2020-03-04 21:49 ` Scott Wood
2020-03-05 3:14 ` Jason Yan
2020-02-06 2:58 ` [PATCH v3 5/6] powerpc/fsl_booke/64: clear the original kernel if randomized Jason Yan
2020-02-20 13:49 ` Christophe Leroy
2020-02-26 2:44 ` Jason Yan
2020-03-04 21:53 ` Scott Wood
2020-03-05 3:20 ` Jason Yan
2020-02-06 2:58 ` [PATCH v3 6/6] powerpc/fsl_booke/kaslr: rename kaslr-booke32.rst to kaslr-booke.rst and add 64bit part Jason Yan
2020-02-20 13:50 ` Christophe Leroy
2020-02-26 2:46 ` Jason Yan
2020-02-13 3:00 ` [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64 Jason Yan
2020-02-20 3:33 ` Jason Yan
2020-02-26 7:16 ` Daniel Axtens
2020-02-26 8:18 ` Jason Yan
2020-02-26 11:41 ` Daniel Axtens
2020-02-27 1:55 ` Jason Yan
2020-02-28 5:53 ` Scott Wood
2020-02-28 6:47 ` Jason Yan
2020-02-29 4:28 ` Scott Wood
2020-02-29 7:27 ` Jason Yan
2020-02-29 22:54 ` Scott Wood
2020-03-02 2:17 ` Jason Yan [this message]
2020-03-02 3:24 ` Scott Wood
2020-03-02 7:12 ` Jason Yan
2020-03-02 8:47 ` Scott Wood
2020-03-02 9:37 ` Jason Yan
2020-03-04 21:21 ` Scott Wood
2020-03-05 3:22 ` Jason Yan
2020-03-04 12:47 [PATCH] vfsprintf: only hash addresses in security environment Jason Yan
2020-03-04 18:34 ` Kees Cook
2020-03-04 21:11 ` [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64 Scott Wood
2020-03-04 22:36 ` Kees Cook
2020-03-05 18:51 ` Linus Torvalds
2020-03-06 18:33 ` Scott Wood
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