Hi Bhupesh,


On Mon, May 28, 2018 at 2:33 AM, Bhupesh Sharma [off-list ref] wrote:

Hi ARM64 maintainers,

[...]

4. Since 'memstart_addr' indicates the start of physical RAM, we
randomize the same on basis of 'memstart_offset_seed' value above.
Also the 'memstart_addr' value is available in '/proc/kallsyms' and
hence can be accessed by user-space applications to read the
'memstart_addr' value.

User space can read, only when a system has either CONFIG_DEVMEM or
CONFIG_PROC_KCORE  enabled. But, we can have a system which has
CONFIG_RANDOMIZE_BASE enabled but none of the kernel memory access
interface (other than kdump/vmcore).

5. Now since the PAGE_OFFSET value is also used by several user space
tools (for e.g. makedumpfile tool uses the same to determine the start
of linear region and hence to read PT_NOTE fields from /proc/kcore), I
am not sure how to read the randomized value of the same in the KASLR
enabled case.

Do we have a use case other than makedumpfile (I mean where we do not
have vmcore access)? For makedumpfile, we have following information
in vmcore, and I hope, that should be sufficient to find physical
address of any symbol from vmcore.

358         VMCOREINFO_NUMBER(VA_BITS);
359         /* Please note VMCOREINFO_NUMBER() uses "%d", not "%x" */
360         vmcoreinfo_append_str("NUMBER(kimage_voffset)=0x%llx\n",
361                                                 kimage_voffset);
362         vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n",
363                                                 PHYS_OFFSET);


Regards
Pratyush