makedumpfile fails on 4.4 longterm kernel with kaslr enabled

[Masaki Tachibana]

Hi Fukui-san

Thank you for the detailed report.
And sorry that makedumpfile doesn't have the enough compatibility.
Unfortunately, my idea is only to disable KASLR.
If no one propose another way, please consider it.

Thanks
Tachibana

> -----Original Message-----
> From: kexec [mailto:kexec-bounces at lists.infradead.org] On Behalf Of daichi1.fukui at toshiba.co.jp
> Sent: Monday, March 26, 2018 10:21 AM
> To: kexec at lists.infradead.org
> Cc: daichi1.fukui at toshiba.co.jp
> Subject: makedumpfile fails on 4.4 longterm kernel with kaslr enabled
> 
> Dear makedumpfile community,
> 
> Hi. My name is Fukui.
> Please help me investigate an error related to makedumpfile.
> 
> When running the latest makedumpfile 1.6.3 on the Linux 4.4 kernel, we get an error:
> 
> -------------------------------------------
> vtop4_x86_64: Can't get a valid pml4.
> readmem: Can't convert a virtual address(22000000) to physical Address
> readmem: type_addr: 0, addr:22000000, size:8
> get_page_offset_x86_64: Can't read page_offset_base
> 
> makedumpfile Failed.
> -------------------------------------------
> 
> After investigating the cause of this error, we found that the following patch fails to work correctly on Linux 4.4 kernel:
> 
> [PATCH v5 2/2] x86_64: Calculate page_offset in case of re-filtering/sadump/virsh dump
> https://sourceforge.net/p/makedumpfile/code/ci/4944f934845c81f28667b4d7d6452edba062e8e2/
> 
> For your information, here is our testing environment.
> Linux kernel version: 4.4.112
> makedumpfile version: 1.6.3
> 
> According to the patch, the get_symbol_addr function gets the address of symbol "page_offset_base".
> 
> +       if (info->kaslr_offset) {
> +               page_offset_base = get_symbol_addr("page_offset_base");
> +               page_offset_base += info->kaslr_offset;
> 
> However, the symbol is available since Linux 4.8, so Linux 4.4 does not have the symbol.
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?id=021182e52fe01c1f7b126f97fd6ba048d
> c4234fd
> 
> In addition, the patch depends on CONFIG_RANDOMIZE_MEMORY, but Linux 4.4 does not support the configuration.
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?id=0483e1fa6e09d4948272680f691dccb1e
> db9677f
> 
> In short, on Linux 4.4, the kaslr patch (x86_64: Calculate page_offset in case of re-filtering/sadump/virsh dump)
> does not work correctly because of lacking both of the symbol and the configuration.
> 
> Some may think why we run makedumpfile on Linux 4.4.
> We aim at building a longterm supportable Linux system on a PC platform.
> Because 4.4 is a longterm release kernel, the kernel is very suitable for our goal.
> 
> Range of this influence can be large because Linux 4.4 will be maintained until 2020.
> See kernel.org for details:
> https://www.kernel.org/category/releases.html
> 
> Can you help us correct the compatibility issue?
> 
> Thanks,
> Fukui
> 
> 
> 
> 
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