ANDROID: 16K: Separate padding from ELF LOAD segment mappings

In has been found that some in-field apps depend on the output of
/proc/*/maps to determine the address ranges of other operations.

With the extension of LOAD segments VMAs to be contiguous in memory,
the apps may perform operations on an area that is not backed by the
underlying file, which results in a SIGBUS. Other apps have crashed
with yet unindentified reasons.

To avoid breaking in-field apps, maintain the output of /proc/*/[s]maps
with PROT_NONE VMAs for the padding pages of LOAD segmetns instead of
showing the segment extensions.

NOTE: This does not allocate actual backing VMAs for the shown
      PROT_NONE mappings.

This approach maintains 2 possible assumptions that userspace (apps)
could be depending on:
   1) That LOAD segment mappings are "contiguous" (not speparated by
      unrelated mappings) in memory.
   2) That no virtual address space is available between mappings of
      consecutive LOAD segments for the same ELF.

For example the output of /proc/*/[s]maps before and after this change
is shown below. Segments maintain PROT_NONE gaps ("[page size compat]")
for app compatiblity but these are not backed by actual slab VMA memory.

Maps Before:

7fb03604d000-7fb036051000 r--p 00000000 fe:09 21935719                   /system/lib64/libnetd_client.so
7fb036051000-7fb036055000 r-xp 00004000 fe:09 21935719                   /system/lib64/libnetd_client.so
7fb036055000-7fb036059000 r--p 00008000 fe:09 21935719                   /system/lib64/libnetd_client.so
7fb036059000-7fb03605a000 rw-p 0000c000 fe:09 21935719                   /system/lib64/libnetd_client.so

Maps After:

7fc707390000-7fc707393000 r--p 00000000 fe:09 21935719                   /system/lib64/libnetd_client.so
7fc707393000-7fc707394000 ---p 00000000 00:00 0                          [page size compat]
7fc707394000-7fc707398000 r-xp 00004000 fe:09 21935719                   /system/lib64/libnetd_client.so
7fc707398000-7fc707399000 r--p 00008000 fe:09 21935719                   /system/lib64/libnetd_client.so
7fc707399000-7fc70739c000 ---p 00000000 00:00 0                          [page size compat]
7fc70739c000-7fc70739d000 rw-p 0000c000 fe:09 21935719                   /system/lib64/libnetd_client.so

Smaps Before:

7fb03604d000-7fb036051000 r--p 00000000 fe:09 21935719                   /system/lib64/libnetd_client.so
Size:                 16 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                  16 kB
Pss:                   0 kB
Pss_Dirty:             0 kB
Shared_Clean:         16 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:           16 kB
Anonymous:             0 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: rd mr mw me
7fb036051000-7fb036055000 r-xp 00004000 fe:09 21935719                   /system/lib64/libnetd_client.so
Size:                 16 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                  16 kB
Pss:                   0 kB
Pss_Dirty:             0 kB
Shared_Clean:         16 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:           16 kB
Anonymous:             0 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: rd ex mr mw me
7fb036055000-7fb036059000 r--p 00008000 fe:09 21935719                   /system/lib64/libnetd_client.so
Size:                 16 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                   4 kB
Pss:                   4 kB
Pss_Dirty:             4 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         4 kB
Referenced:            4 kB
Anonymous:             4 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: rd mr mw me ac
7fb036059000-7fb03605a000 rw-p 0000c000 fe:09 21935719                   /system/lib64/libnetd_client.so
Size:                  4 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                   4 kB
Pss:                   4 kB
Pss_Dirty:             4 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         4 kB
Referenced:            4 kB
Anonymous:             4 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: rd wr mr mw me ac

Smaps After:

7fc707390000-7fc707393000 r--p 00000000 fe:09 21935719                   /system/lib64/libnetd_client.so
Size:                 12 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                  12 kB
Pss:                   0 kB
Shared_Clean:         12 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:           12 kB
Anonymous:             0 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: rd mr mw me ??
7fc707393000-7fc707394000 ---p 00000000 00:00 0                          [page size compat]
Size:                  4 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                   0 kB
Pss:                   0 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:            0 kB
Anonymous:             0 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: mr mw me
7fc707394000-7fc707398000 r-xp 00004000 fe:09 21935719                   /system/lib64/libnetd_client.so
Size:                 16 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                  16 kB
Pss:                   0 kB
Shared_Clean:         16 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:           16 kB
Anonymous:             0 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: rd ex mr mw me
7fc707398000-7fc707399000 r--p 00008000 fe:09 21935719                   /system/lib64/libnetd_client.so
Size:                  4 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                   4 kB
Pss:                   4 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         4 kB
Referenced:            4 kB
Anonymous:             4 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: rd mr mw me ac ?? ??
7fc707399000-7fc70739c000 ---p 00000000 00:00 0                          [page size compat]
Size:                 12 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                   0 kB
Pss:                   0 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:            0 kB
Anonymous:             0 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: mr mw me ac
7fc70739c000-7fc70739d000 rw-p 0000c000 fe:09 21935719                   /system/lib64/libnetd_client.so
Size:                  4 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                   4 kB
Pss:                   4 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         4 kB
Referenced:            4 kB
Anonymous:             4 kB
LazyFree:              0 kB
AnonHugePages:         0 kB
ShmemPmdMapped:        0 kB
FilePmdMapped:         0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0
VmFlags: rd wr mr mw me ac

Bug: 330117029
Bug: 327600007
Bug: 330767927
Bug: 328266487
Bug: 329803029
Change-Id: I12bf2c106fafc74a500d79155b81dde5db42661e
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>