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From: Freeman Zhang <freeman.zhang1992@gmail.com>
Subject: Removal of the kernel code/data/bss resources does break kexec/kdump
Message-ID: <570F6D99.6090400@gmail.com>
Date: Thu, 14 Apr 2016 18:14:49 +0800
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To: torvalds@linux-foundation.org
Cc: ed@abdsec.com, kexec@lists.infradead.org

Mr. Torvalds,

I do notice your recent commit:

> commit c4004b02f8e5b9ce357a0bb1641756cc86962664
> Author: Linus Torvalds <torvalds@linux-foundation.org>
> Date:   Wed Apr 6 13:45:07 2016 -0700
>
>     x86: remove the kernel code/data/bss resources from /proc/iomem
>
> Let's see if anybody even notices.  I doubt anybody uses this, and it
> does expose addresses that should be randomized, so let's just remove
> the code.  It's old and traditional, and it used to be cute, but we
> should have removed this long ago.
>
> If it turns out anybody notices and this breaks something, we'll have to
> revert this, and maybe we'll end up using other approaches instead
> (using %pK or similar).  But removing unnecessary code is always the
> preferred option.

Removal of these information causes 'kexec/kdump' to fail in the newer
kernel, as 'kexec/arch/i386/crashdump-x86.c' is coded this way:


/* Read kernel physical load addr from the file returned by proc_iomem()
 * (Kernel Code) and store in kexec_info */
static int get_kernel_paddr(struct kexec_info *UNUSED(info),
                            struct crash_elf_info *elf_info)
{
               ...

      if (parse_iomem_single("Kernel code\n", &start, NULL) == 0) {
              elf_info->kern_paddr_start = start;
              dbgprintf("kernel load physical addr start = 0x%016Lx\n",
                        (unsigned long long)start);
              return 0;
      }

     fprintf(stderr, "Cannot determine kernel physical load addr\n");
     return -1;
}


Should we revert this commit, or update kexec/kdump code?


Great respect!
Freeman

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