Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

From: Pratyush Anand
Date: Wed Jan 25 2017 - 01:52:06 EST

Hi Dave,

On Wednesday 25 January 2017 11:59 AM, Dave Young wrote:
Hi Pratyush
On 01/25/17 at 10:14am, Pratyush Anand wrote:
Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
not true and could be misleading, since 0 is a valid physical address.
I do not know the history of /proc/kcore, so a question is why the
p_addr was set as 0, if there were some reasons and if this could cause
some risk or breakage.

I do not know why it was 0, which is a valid physical address. But certainly, it might break some user space tools, and those need to be fixed. For example, see following code from kexec-tools


435 if ((phdr->p_paddr + phdr->p_memsz) < phdr->p_paddr) {
436 /* The memory address wraps */
437 if (probe_debug) {
438 fprintf(stderr, "ELF address wrap around\n");
439 }
440 return -1;
441 }

We do not need to perform above check for an invalid physical address.

I think, kexec-tools and makedumpfile will need fixup. I already have those fixup which will be sent upstream once this patch makes through.
Pro with this approach is that, it will help to calculate variable like page_offset, phys_base from PT_LOAD even when they are randomized and therefore will reduce many variable and version specific values in user space tools.