Re: [PATCH] makedumpfile/s390: Add get_kaslr_offset() for s390x

[lijiang <lijiang@redhat.com>]

> Hi Lianbo,
> 
>> -----Original Message-----
>> 在 2019年12月26日 11:38, lijiang 写道:
>>> Hi, Kazu and Mikhail,
>>>
>>>> Hi Mikhail,
>>>>
>>>>> -----Original Message-----
>>>>> Hi,
>>>>>
>>>>> On 12.12.2019 17:12, Kazuhito Hagio wrote:
>>>>>> Hi Mikhail,
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> Hello Kazu,
>>>>>>>
>>>>>>> I think we can try to generalize the kaslr offset extraction.
>>>>>>> I won't speak for other architectures, but for s390 that get_kaslr_offset_arm64()
>>>>>>> should work fine. The only concern of mine is this TODO statement:
>>>>>>>
>>>>>>> if (_text <= vaddr && vaddr <= _end) {
>>>>>>> 	DEBUG_MSG("info->kaslr_offset: %lx\n", info->kaslr_offset);
>>>>>>> 	return info->kaslr_offset;
>>>>>>> 	} else {
>>>>>>> 	/*
>>>>>>> 	* TODO: we need to check if it is vmalloc/vmmemmap/module
>>>>>>> 	* address, we will have different offset
>>>>>>> 	*/
>>>>>>> 	return 0;
>>>>>>> }
>>>>>>>
>>>>>>> Could you explain this one?
>>>>>>
>>>>>> Probably it was considered that the check would be needed to support
>>>>>> the whole KASLR behavior when get_kaslr_offset_x86_64() was written
>>>>>> originally.
>>>>>>
>>>>>> But in the current makedumpfile for x86_64 and arm64 supporting KASLR,
>>>>>> the offset we need is the one for symbol addresses in vmlinux only.
>>>>>> As I said below, module symbol addresses are retrieved from vmcore.
>>>>>> Other addresses should not be passed to the function for now, as far
>>>>>> as I know.
>>>>>>
>>>>>> So I think the TODO comment is confusing, and it would be better to
>>>>>> remove it or change it to something like:
>>>>>> /*
>>>>>>  * Returns 0 if vaddr does not need the offset to be added,
>>>>>>  * e.g. for module address.
>>>>>>  */
>>>>>>
>>>>>> But if s390 uses get_kaslr_offset() in its arch-specific code to
>>>>>> adjust addresses other than kernel text address, we might need to
>>>>>> modify it for s390, not generalize it.
>>>>>
>>>>> Currently, s390 doesn't use get_kaslr_offset() in its arch-specific
>>>>> code.
>>>>
>>>> OK, I pushed a patch that generalizes it to my test repository.
>>>> Could you enable s390 to use it and test?
>>>> https://github.com/k-hagio/makedumpfile/tree/add-get_kaslr_offset_general
>>>>
>>>
>>> I enabled it on s390 as below and tested, it worked.
> 
> Thank you for testing.
> 
It's my pleasure. 

>>>
>>> @@ -1075,7 +1075,7 @@ int is_iomem_phys_addr_s390x(unsigned long addr);
>>>  #define get_phys_base()                stub_true()
>>>  #define get_machdep_info()     get_machdep_info_s390x()
>>>  #define get_versiondep_info()  stub_true()
>>> -#define get_kaslr_offset(X)    stub_false()
>>> +#define get_kaslr_offset(X)    get_kaslr_offset_general(X)
>>>  #define vaddr_to_paddr(X)      vaddr_to_paddr_s390x(X)
>>>
>>> But, there is still a problem that needs to be improved. In the find_kaslr_offsets(),
>>> the value of SYMBOL(_stext) is always 0(zero) and it is passed to the get_kaslr_offset().
>>> For the following code in the get_kaslr_offset_general(), it does not work as expected.
>>> ...
>>> 	if (_text <= vaddr && vaddr <= _end)
>>> 		return info->kaslr_offset;
>>> 	else
>>> 		return 0;
> 
> I don't know why the SYMBOL(_stext) is passed to the get_kaslr_offset() there, but
> since the return value of get_kaslr_offset() is not used in the find_kaslr_offsets(),
> it's meaningless and not harmful. So it is not worth doing READ_SYMBOL(_stext) there
> for now.
> 
Sounds good.

>>
>> In addition, the above code confused me, it will always return 0 on s390(please refer to my logs).
> 
> The aim of get_kaslr_offset() here is only setting info->kaslr_offset to the value
> from vmcoreinfo for the SYMBOL_INIT() macro.
> (get_kaslr_offset() returns the kaslr offset in the resolve_config_entry().)
> 
Thanks for your explanation, Kazu.

> But yeah, the get_kaslr_offset(SYMBOL(_stext)) is confusing and not good.
> Passing 0 might be a bit better..?
> 
Yes, looks good to me.

Lianbo
> Thanks,
> Kazu
> 
>>
>> Thanks.
>>
>>> ...
>>> Here is my log:
>>> get_kaslr_offset_general: info->kaslr_offset: 67ebc000, _text:100000, _end:10ba000, vaddr:0
>>>
>>> After applied the following patch, got the expected result.
>>>  int
>>>  find_kaslr_offsets()
>>>  {
>>> @@ -3973,6 +4042,11 @@ find_kaslr_offsets()
>>>          * called this function between open_vmcoreinfo() and
>>>          * close_vmcoreinfo()
>>>          */
>>> +       READ_SYMBOL("_stext", _stext);
>>> +       if (SYMBOL(_stext) == NOT_FOUND_SYMBOL) {
>>> +                ERRMSG("Can't get the symbol of _stext.\n");
>>> +                goto out;
>>> +       }
>>>         get_kaslr_offset(SYMBOL(_stext));
>>>
>>> Here is my log:
>>> get_kaslr_offset_general: info->kaslr_offset: 67ebc000, _text:100000, _end:10ba000, vaddr:67fbc000
>>>
>>> Basically, before using the value of SYMBOL(_stext), need to ensure that the SYMBOL(_stext) is parsed
>>> correctly.
>>>
>>> Thanks.
>>>
>>>> Thanks,
>>>> Kazu
>>>>
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Kazu
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Mikhail
>>>>>>>
>>>>>>> On 09.12.2019 23:02, Kazuhito Hagio wrote:
>>>>>>>> Hi Mikhail,
>>>>>>>>
>>>>>>>> Sorry for late reply.
>>>>>>>>
>>>>>>>>> -----Original Message-----
>>>>>>>>> Since kernel v5.2 KASLR is supported on s390. In makedumpfile however no
>>>>>>>>> support has been added yet. This patch adds the arch specific function
>>>>>>>>> get_kaslr_offset() for s390x.
>>>>>>>>> Since the values in vmcoreinfo are already relocated, the patch is
>>>>>>>>> mainly relevant for vmlinux processing (-x option).
>>>>>>>>
>>>>>>>> In the current implementation of makedumpfile, the get_kaslr_offset(vaddr)
>>>>>>>> is supposed to return the KASLR offset only when the offset is needed to
>>>>>>>> add to the vaddr.  So generally symbols from kernel (vmlinux) need it, but
>>>>>>>> symbols from modules are resolved dynamically and don't need the offset.
>>>>>>> \>
>>>>>>>> This patch always returns the offset if any, as a result, I guess this patch
>>>>>>>> will not work as expected with module symbols in filter config file.
>>>>>>>>
>>>>>>>> So... How about making get_kaslr_offset_arm64() general for other archs
>>>>>>>> (get_kaslr_offset_general() or something), then using it also for s390?
>>>>>>>> If OK, I can do that generalization.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Kazu
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Signed-off-by: Philipp Rudo <prudo@linux.ibm.com>
>>>>>>>>> Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
>>>>>>>>> ---
>>>>>>>>>  arch/s390x.c   | 32 ++++++++++++++++++++++++++++++++
>>>>>>>>>  makedumpfile.h |  3 ++-
>>>>>>>>>  2 files changed, 34 insertions(+), 1 deletion(-)
>>>>>>>>>
>>>>>>>>> diff --git a/arch/s390x.c b/arch/s390x.c
>>>>>>>>> index bf9d58e..892df14 100644
>>>>>>>>> --- a/arch/s390x.c
>>>>>>>>> +++ b/arch/s390x.c
>>>>>>>>> @@ -122,6 +122,38 @@ get_machdep_info_s390x(void)
>>>>>>>>>  	return TRUE;
>>>>>>>>>  }
>>>>>>>>>
>>>>>>>>> +unsigned long
>>>>>>>>> +get_kaslr_offset_s390x(unsigned long vaddr)
>>>>>>>>> +{
>>>>>>>>> +	unsigned int i;
>>>>>>>>> +	char buf[BUFSIZE_FGETS], *endp;
>>>>>>>>> +
>>>>>>>>> +	if (!info->file_vmcoreinfo)
>>>>>>>>> +		return FALSE;
>>>>>>>>> +
>>>>>>>>> +	if (fseek(info->file_vmcoreinfo, 0, SEEK_SET) < 0) {
>>>>>>>>> +		ERRMSG("Can't seek the vmcoreinfo file(%s). %s\n",
>>>>>>>>> +		       info->name_vmcoreinfo, strerror(errno));
>>>>>>>>> +		return FALSE;
>>>>>>>>> +	}
>>>>>>>>> +
>>>>>>>>> +	while (fgets(buf, BUFSIZE_FGETS, info->file_vmcoreinfo)) {
>>>>>>>>> +		i = strlen(buf);
>>>>>>>>> +		if (!i)
>>>>>>>>> +			break;
>>>>>>>>> +		if (buf[i - 1] == '\n')
>>>>>>>>> +			buf[i - 1] = '\0';
>>>>>>>>> +		if (strncmp(buf, STR_KERNELOFFSET,
>>>>>>>>> +			    strlen(STR_KERNELOFFSET)) == 0) {
>>>>>>>>> +			info->kaslr_offset =
>>>>>>>>> +				strtoul(buf + strlen(STR_KERNELOFFSET), &endp, 16);
>>>>>>>>> +			DEBUG_MSG("info->kaslr_offset: %lx\n", info->kaslr_offset);
>>>>>>>>> +		}
>>>>>>>>> +	}
>>>>>>>>> +
>>>>>>>>> +	return info->kaslr_offset;
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>>  static int
>>>>>>>>>  is_vmalloc_addr_s390x(unsigned long vaddr)
>>>>>>>>>  {
>>>>>>>>> diff --git a/makedumpfile.h b/makedumpfile.h
>>>>>>>>> index ac11e90..26f6247 100644
>>>>>>>>> --- a/makedumpfile.h
>>>>>>>>> +++ b/makedumpfile.h
>>>>>>>>> @@ -1071,11 +1071,12 @@ unsigned long long vaddr_to_paddr_ppc(unsigned long vaddr);
>>>>>>>>>  int get_machdep_info_s390x(void);
>>>>>>>>>  unsigned long long vaddr_to_paddr_s390x(unsigned long vaddr);
>>>>>>>>>  int is_iomem_phys_addr_s390x(unsigned long addr);
>>>>>>>>> +unsigned long get_kaslr_offset_s390x(unsigned long vaddr);
>>>>>>>>>  #define find_vmemmap()		stub_false()
>>>>>>>>>  #define get_phys_base()		stub_true()
>>>>>>>>>  #define get_machdep_info()	get_machdep_info_s390x()
>>>>>>>>>  #define get_versiondep_info()	stub_true()
>>>>>>>>> -#define get_kaslr_offset(X)	stub_false()
>>>>>>>>> +#define get_kaslr_offset(X)	get_kaslr_offset_s390x(X)
>>>>>>>>>  #define vaddr_to_paddr(X)	vaddr_to_paddr_s390x(X)
>>>>>>>>>  #define paddr_to_vaddr(X)	paddr_to_vaddr_general(X)
>>>>>>>>>  #define is_phys_addr(X)		is_iomem_phys_addr_s390x(X)
>>>>>>>>> --
>>>>>>>>> 2.17.1
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>>>
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>>>
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>>
> 


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