On 2016-04-14 06:14, Freeman Zhang wrote:
Mr. Torvalds,
I do notice your recent commit:
commit c4004b02f8e5b9ce357a0bb1641756cc86962664
Author: Linus Torvalds <torva...@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
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