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From: Dave Anderson <anderson@redhat.com>
To: Dave Young <dyoung@redhat.com>, kexec@lists.infradead.org
Cc: Pratyush Anand <panand@redhat.com>,
	ats-kumagai@wm.jp.nec.com, bhe@redhat.com
Subject: Re: [PATCH Makedumpfile 0/4] x86_64: Fix page_offset for randomized base enabled
Date: Thu, 27 Oct 2016 11:41:51 -0400 (EDT)	[thread overview]
Message-ID: <1344182812.8599658.1477582911159.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <595835228.8595706.1477581920601.JavaMail.zimbra@redhat.com>



----- Original Message -----
> 
> 
> ----- Original Message -----
> 
> >   
> > That being said, my recent 4.8 and 4.9 KASLR testing has been on live
> > systems and compressed kdumps, so the old tried-and-true manner of
> > calculating the phys_base from the ELF PT_LOAD segments apparently
> > no longer works with KASLR.
> > 
> > It would be so much more helpful if the VMCOREINFO data in the ELF
> > header stored the actual phys_base value instead of its symbol value:
> > 
> >   crash> help -D
> >   ...
> >   SYMBOL(phys_base)=ffffffffa740b010
> >   ...
> > 
> > which is completely useless unless the phys_base value is known.
> > 
> > Anyway, can you send me the makedumpfile code that calculates the
> > phys_base value?
> > 
> > Dave
> 
> As it turns out, the problem with the crash utility is that it has to
> calculate phys_base well before it even knows the kernel has been relocated
> by KASLR.  So when it sees the __START_KERNEL_map PT_LOAD segment, it
> mistakes
> it for the kernel modules' virtual address region and skips it.
> 
> The kernel has this:
> 
>   #if defined(CONFIG_RANDOMIZE_BASE)
>   #define KERNEL_IMAGE_SIZE       (1024 * 1024 * 1024)
>   #else
>   #define KERNEL_IMAGE_SIZE       (512 * 1024 * 1024)
>   #endif
> 
> and then this:
> 
>   #define MODULES_VADDR    (__START_KERNEL_map + KERNEL_IMAGE_SIZE)
> 
> So with KASLR, MODULES_VADDR gets pushed up from the traditional ffffffffa0000000
> up to ffffffffc0000000.
> 
> So I'm curious as to what you use in makedumpfile to determine whether
> CONFIG_RANDOMIZE_BASE has been configured?
> 
> Thanks,
>   Dave

Hey, sorry, I didn't notice that this was added upstream:

  commit 1303a27c9c32020a3b6ac89be270d2ab1f28be24
  Author: Baoquan He <bhe@redhat.com>
  Date:   Wed Sep 9 15:39:03 2015 -0700

    kexec: export KERNEL_IMAGE_SIZE to vmcoreinfo
    
With that in place, it will be an easy fix for the crash utility.

Thanks,
  Dave










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  reply	other threads:[~2016-10-27 15:42 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-24 16:48 [PATCH Makedumpfile 0/4] x86_64: Fix page_offset for randomized base enabled Pratyush Anand
2016-10-24 16:48 ` [PATCH] temp Pratyush Anand
2016-10-24 16:51   ` Pratyush Anand
2016-10-24 16:48 ` [PATCH Makedumpfile 1/4] x86_64: Calculate page_offset from pt_load Pratyush Anand
2016-10-27  6:03   ` Pratyush Anand
2016-11-02  7:40     ` Atsushi Kumagai
2016-11-02  8:02       ` bhe
2016-11-04 10:35         ` Atsushi Kumagai
2016-10-24 16:48 ` [PATCH Makedumpfile 2/4] x86_64: translate all VA to PA using page table values Pratyush Anand
2016-10-25  9:20   ` Atsushi Kumagai
2016-10-25 15:12     ` Pratyush Anand
2016-10-25 23:28       ` bhe
2016-10-26  6:24         ` Atsushi Kumagai
2016-10-24 16:48 ` [PATCH Makedumpfile 3/4] x86_64: kill is_vmalloc_addr_x86_64() Pratyush Anand
2016-10-24 16:48 ` [PATCH Makedumpfile 4/4] x86_64: kill some unused initialization Pratyush Anand
2016-10-25  9:17 ` [PATCH Makedumpfile 0/4] x86_64: Fix page_offset for randomized base enabled Louis Bouchard
2016-10-25  9:20   ` Pratyush Anand
2016-10-27  2:37 ` Dave Young
2016-10-27  2:54   ` Dave Young
2016-10-27  6:19     ` Dave Young
     [not found]       ` <926225735.8567580.1477574985798.JavaMail.zimbra@redhat.com>
2016-10-27 15:25         ` Dave Anderson
2016-10-27 15:41           ` Dave Anderson [this message]
2016-10-28  2:04             ` Dave Young
2016-10-27 15:59           ` Pratyush Anand
2016-10-27  3:25   ` Baoquan He
2016-10-27  5:11   ` Pratyush Anand
     [not found] <mailman.65015.1477545113.1639.kexec@lists.infradead.org>
2016-10-27 13:25 ` Dave Anderson

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