[Crash-utility] [PATCH] x86_64: Fix that Particular kvaddr is converted to wrong paddr (RHEL6 x86_64)

[Nakajima Akira]

> But because it is such a fundamental change that
> you are proposing, it might make sense to create a check/macro that is specific to
> the vsyscall region.   

What is check/macro? How do we check what?
Certainly, these addresses are vsyscall region.
After applying this patch, crash looks read vsyscall region correctly.



crash> sym vsyscall
    // abbreviation //
  ffffffffff600000 (t) .vsyscall_0
  ffffffffff600140 (t) .vsyscall_fn
  ffffffffff600180 (d) .vsyscall_gtod_data
  ffffffffff600180 (D) __vsyscall_gtod_data
  ffffffffff600400 (t) .vsyscall_1
  ffffffffff600800 (t) .vsyscall_2
  ffffffffff700680 (A) VDSO64_vsyscall_gtod_data

crash> sym VDSO
symbol not found: VDSO
possible alternatives:
  ffffffffff700000 (A) VDSO64_PRELINK
  ffffffffff700670 (A) VDSO64_jiffies
  ffffffffff700678 (A) VDSO64_vgetcpu_mode
  ffffffffff700680 (A) VDSO64_vsyscall_gtod_data


//////// not patched /////////
crash> dis .vsyscall_0
0xffffffffff600000 <.vsyscall_0>:       add    %al,(%rax)
0xffffffffff600002 <vgettimeofday+2>:   add    %al,(%rax)
0xffffffffff600004 <vgettimeofday+4>:   add    %al,(%rax)
0xffffffffff600006 <vgettimeofday+6>:   add    %al,(%rax)
0xffffffffff600008 <vgettimeofday+8>:   add    %al,(%rax)
0xffffffffff60000a <vgettimeofday+10>:  add    %al,(%rax)
    // abbreviation //


//////// after applying this patch /////////
crash> dis .vsyscall_0
0xffffffffff600000 <.vsyscall_0>:       push   %rbp
0xffffffffff600001 <vgettimeofday+1>:   mov    %rsp,%rbp
0xffffffffff600004 <vgettimeofday+4>:   push   %r13
0xffffffffff600006 <vgettimeofday+6>:   push   %r12
0xffffffffff600008 <vgettimeofday+8>:   mov    %rdi,%r12
0xffffffffff60000b <vgettimeofday+11>:  push   %rbx
0xffffffffff60000c <vgettimeofday+12>:  mov    %rsi,%rbx
0xffffffffff60000f <vgettimeofday+15>:  sub    $0x8,%rsp
0xffffffffff600013 <vgettimeofday+19>:  test   %rdi,%rdi
0xffffffffff600016 <vgettimeofday+22>:  je     0xffffffffff6000d5 <vgettimeofday+213>
    // abbreviation //


On 2015/12/22 22:42, Dave Anderson wrote:
> 
> 
> ----- Original Message -----
>> I didn't check XEN HYPER MODE, I don't have XEN.
>> If we need similar statement "if (kvaddr < MODULES_END)"
>>  please add inside in "if (XEN_HYPER_MODE())" (1859 at x86_64_kvtop)
>>
>>
>>
>>
>> >From ed300b74998e0923313e4fd14b9a41e305942b44 Mon Sep 17 00:00:00 2001
>> From: Nakajima Akira <nakajima.akira at nttcom.co.jp>
>> Date: Tue, 22 Dec 2015 15:46:42 +0900
>> Subject: [PATCH] Fix that particular kvaddr is converted to wrong paddr
>>
>> BUG INFO
>> Particular kvaddr is converted to wrong paddr.
>> You can see this bug on RHEL6_x86_64. (at present only RHEL6)
>>  (I checked RHEL5, RHEL7, Fedora21, Fedora23)
> 
> 
> I am out of the office until January 4th (only checking email until then), and will not
> be able to look into this until then.  But because it is such a fundamental change that
> you are proposing, it might make sense to create a check/macro that is specific to
> the vsyscall region.   
> 
> Thanks,
>   Dave
>  
>>
>> from /proc/kallsyms
>> ffffffffff6008c0 D __jiffies
>>
>> /////////// wrong ///////////
>> crash> vtop ffffffffff6008c0
>> VIRTUAL           PHYSICAL
>> ffffffffff6008c0  7f6008c0
>>
>>       PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>> ffffea00000623b8   1c11000                0        0  1 20000000000400
>> reserved
>>
>>
>> crash> rd ffffffffff6008c0
>> ffffffffff6008c0:  0000000000000000                    ........
>>
>>
>> /////////// correct ///////////
>> crash> vtop ffffffffff6008c0
>> VIRTUAL           PHYSICAL
>> ffffffffff6008c0  1c118c0
>>
>>       PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>> ffffea00000623b8   1c11000                0        0  1 20000000000400
>> reserved
>>
>>
>> crash> rd ffffffffff6008c0
>> ffffffffff6008c0:  00000000ffffe43a                    :.......
>>
>> Reported-by: Nakajima Akira <nakajima.akira at nttcom.co.jp>
>> Signed-off-by: Nakajima Akira <nakajima.akira at nttcom.co.jp>
>>
>> ---
>>  x86_64.c |   28 +++++++++++++++-------------
>>  1 files changed, 15 insertions(+), 13 deletions(-)
>>
>> diff --git a/x86_64.c b/x86_64.c
>> index ff6fdd5..dab4d43 100644
>> --- a/x86_64.c
>> +++ b/x86_64.c
>> @@ -1872,19 +1872,21 @@ x86_64_kvtop(struct task_context *tc, ulong kvaddr,
>> physaddr_t *paddr, int verbo
>>                 		fprintf(fp, "PAGE DIRECTORY: %lx\n", *pml4);
>>  		}
>>  	} else {
>> -        	if (!vt->vmalloc_start) {
>> -                	*paddr = x86_64_VTOP(kvaddr);
>> -                	return TRUE;
>> -        	}
>> -
>> -        	if (!IS_VMALLOC_ADDR(kvaddr)) {
>> -                	*paddr = x86_64_VTOP(kvaddr);
>> -                	if (!verbose)
>> -                        	return TRUE;
>> -        	}
>> -
>> -		if (XEN() && (kt->xen_flags & WRITABLE_PAGE_TABLES))
>> -			return (x86_64_kvtop_xen_wpt(tc, kvaddr, paddr, verbose));
>> +		if (kvaddr < MODULES_END) {
>> +	        	if (!vt->vmalloc_start) {
>> +	                	*paddr = x86_64_VTOP(kvaddr);
>> +	                	return TRUE;
>> +	        	}
>> +
>> +	        	if (!IS_VMALLOC_ADDR(kvaddr)) {
>> +	                	*paddr = x86_64_VTOP(kvaddr);
>> +	                	if (!verbose)
>> +	                        	return TRUE;
>> +	        	}
>> +
>> +			if (XEN() && (kt->xen_flags & WRITABLE_PAGE_TABLES))
>> +				return (x86_64_kvtop_xen_wpt(tc, kvaddr, paddr, verbose));
>> +		}
>>  
>>   		/*
>>  		 *  pgd = pgd_offset_k(addr);
>> --
>> 1.7.1
>>
>>
>> --
>> Crash-utility mailing list
>> Crash-utility at redhat.com
>> https://www.redhat.com/mailman/listinfo/crash-utility
> 
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