[Bug ld/29639] New: Bumping common page size to 16 KiB on ARM64?

[rui314 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29639

            Bug ID: 29639
           Summary: Bumping common page size to 16 KiB on ARM64?
           Product: binutils
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: rui314 at gmail dot com
  Target Milestone: ---

Currently, the default value of `-z max-page-size` and `-z common-page-size`
are 65536 and 4096 on ARM64, respectively. That means an executable created by
GNU ld with the default settings works on any system whose page size is equal
to or smaller than 65536, but the RELRO segment may not be protected on systems
with >4096 byte pages.

RELRO works on page granularity. When GNU ld creates a PT_GNU_RELRO segment, it
uses the common page size as a page size. At runtime, both the start and the
end address of a PT_GNU_RELRO segment are _rounded down_ to the actual system's
page size. So, if the common page size is smaller than the max page size, it is
not guaranteed that an entire RELRO segment becomes read-only after process
initialization.

I think this can cause a security issue. Asahi Linux uses 16 KiB pages, so the
above situation is I think becoming real. Maybe we should bump the common page
size to 16 KiB on ARM64?

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