On 2016-04-14 06:14, Freeman Zhang wrote:
> Mr. Torvalds,
>
> I do notice your recent commit:
>
>> commit c4004b02f8e5b9ce357a0bb1641756cc86962664
>> Author: Linus Torvalds <torvalds at 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?
>
Ubuntu also has some issues with this patch. I think there are several
issue that hasn't been noticed.
It would be better you to revert this patch. Updating kexec/kdump might
not solve this problem.
Kees Cook proposed to write a %pK formatted patch. This would solve most
of the problems.
https://lkml.org/lkml/2016/4/14/18
Best regards!
Emrah Demir
