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Subject: Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64
To:     Scott Wood <oss@buserror.net>, Daniel Axtens <dja@axtens.net>,
        <mpe@ellerman.id.au>, <linuxppc-dev@lists.ozlabs.org>,
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        <kernel-hardening@lists.openwall.com>, <me@tobin.cc>
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From:   Jason Yan <yanaijie@huawei.com>
Message-ID: <17658c2b-9eb8-cee9-e9a2-93d316a401b1@huawei.com>
Date:   Mon, 2 Mar 2020 15:12:39 +0800
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在 2020/3/2 11:24, Scott Wood 写道:
> On Mon, 2020-03-02 at 10:17 +0800, Jason Yan wrote:
>>
>> 在 2020/3/1 6:54, Scott Wood 写道:
>>> On Sat, 2020-02-29 at 15:27 +0800, Jason Yan wrote:
>>>>
>>>> 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.
> 
> I'm more concerned about the stack address for wading through a raw stack dump
> (to find function call arguments, etc).  The return address does help confirm
> that I'm on the right stack frame though, and also makes looking up a line
> number slightly easier than having to look up a symbol address and then add
> the offset (at least for non-module addresses).
> 
> As a random aside, the mismatch between Linux printing a hex offset and GDB
> using decimal in disassembly is annoying...
> 

OK, I will send a RFC patch to add a new format specifier such as "%pk" 
or change the exsiting "%pK" to print raw value of addresses when KASLR 
is disabled and print hash value of addresses when KASLR is enabled. 
Let's see what the printk guys would say :)


> -Scott
> 
> 
> 
> .
>