[PATCH v3 0/2] Selecting Load Addresses According to p_align

Chris Kennelly
2020-08-20T17:10:16Z

The current ELF loading mechancism provides page-aligned mappings. This
can lead to the program being loaded in a way unsuitable for
file-backed, transparent huge pages when handling PIE executables.

While specifying -z,max-page-size=0x200000 to the linker will generate
suitably aligned segments for huge pages on x86_64, the executable needs
to be loaded at a suitably aligned address as well. This alignment
requires the binary's cooperation, as distinct segments need to be
appropriately paddded to be eligible for THP.

For binaries built with increased alignment, this limits the number of
bits usable for ASLR, but provides some randomization over using fixed
load addresses/non-PIE binaries.

Changes V2 -> V3:
* Minor code tweaks based on off-thread feedback

Changes V1 -> V2:
* Added test

Chris Kennelly (2):
fs/binfmt_elf: Use PT_LOAD p_align values for suitable start address.
Add self-test for verifying load alignment.

fs/binfmt_elf.c | 23 +++++++
tools/testing/selftests/exec/.gitignore | 1 +
tools/testing/selftests/exec/Makefile | 9 ++-
tools/testing/selftests/exec/load_address.c | 68 +++++++++++++++++++++
4 files changed, 99 insertions(+), 2 deletions(-)
create mode 100644 tools/testing/selftests/exec/load_address.c

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2.28.0.297.g1956fa8f8d-goog