/proc/kcore: update physical address for kcore ram and text

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.

User space tools like makedumpfile needs to know physical address for
PT_LOAD segments of direct mapped regions.  Therefore this patch updates
paddr for such regions.  It also sets an invalid paddr (-1) for other
regions, so that user space tool can know whether a physical address
provided in PT_LOAD is correct or not.

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

kexec/kexec-elf.c:build_mem_phdrs()

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

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.

Having an ASLR offset information can help to translate an identity
mapped virtual address to a physical address.  But that would be an
additional field in PT_LOAD header structure and an arch dependent
value.

Moreover, sending a valid physical address like 0 does not seem right.
So, IMHO it is better to fix that and send valid physical address when
available (identity mapped).

Link: http://lkml.kernel.org/r/f951340d2917cdd2a329fae9837a83f2059dc3b2.1485318868.git.panand@redhat.com
Signed-off-by: Pratyush Anand <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Dave Anderson <[email protected]>
Cc: Atsushi Kumagai <[email protected]>
Cc: Simon Horman <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Pratyush Anand

fs/proc/kcore.c

@@ -373,7 +373,10 @@ static void elf_kcore_store_hdr(char *bufp, int nphdr, int dataoff)
 		phdr->p_flags	= PF_R|PF_W|PF_X;
 		phdr->p_offset	= kc_vaddr_to_offset(m->addr) + dataoff;
 		phdr->p_vaddr	= (size_t)m->addr;
-		phdr->p_paddr	= 0;
+		if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
+			phdr->p_paddr	= __pa(m->addr);
+		else
+			phdr->p_paddr	= (elf_addr_t)-1;
 		phdr->p_filesz	= phdr->p_memsz	= m->size;
 		phdr->p_align	= PAGE_SIZE;
 	}