[Bug 291446] /libexec/ld-elf.so.1 not branded properly on riscv, breaks manual activation via ldd

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=291446

--- Comment #11 from commit-hook@FreeBSD.org ---
A commit in branch main references this bug:

URL:
https://cgit.FreeBSD.org/src/commit/?id=5d58198ccc2b562098ee5fc4898013622b32b065

commit 5d58198ccc2b562098ee5fc4898013622b32b065
Author:     Jessica Clarke <jrtc27@FreeBSD.org>
AuthorDate: 2025-12-08 13:01:57 +0000
Commit:     Jessica Clarke <jrtc27@FreeBSD.org>
CommitDate: 2025-12-08 13:01:57 +0000

    imgact_elf: Fix off-by-one in note size check

    Prior to c86af2cc4cd1 ("imgact_elf: Check note body sizes"), this was
    note_name + n_namesz >= note_end, which checks that there is at least
    one byte after the unpadded name (which could be either padding or
    data), and given our notes always have data with them this was fine.
    However, once we started checking the padded name (note that "FreeBSD\0"
    is already a multiple of 4 bytes, so has no padding) and data, this
    turned into checking that there is at least one byte after the unpadded
    data, and since our ELF notes already have a multiple of 4 bytes for
    their data and therefore have no padding, this means that we are now
    checking that there is at least one byte after the ELF note, which is
    not going to be the case for the last ELF note. Instead, switch this to
    a strict greater than, as should be used when comparing one-past-the-end
    pointers, which both sides of the inequality are.

    For executables, this was generally not a problem in reality, since the
    last of our ELF notes is NT_FREEBSD_NOINIT_TAG, which isn't read by the
    kernel. However, ld-elf.so.1 (and libcompat variants), like shared
    libraries, only has NT_FREEBSD_ABI_TAG, which meant the kernel did not
    see this ELF note when directly executing it (e.g. as done by ldd), and
    on RISC-V this is the only branding present, so doing so would fail with
    ENOEXEC. This does also mean on non-RISC-V direct exec ld-elf.so.1 runs
    with the wrong p_osrel, but given it sets kern.proc.osrel.PID to the
    executable's NT_FREEBSD_ABI_TAG that it loads, this probably doesn't
    matter in practice.

    PR:             291446
    Reported by:    bdragon
    Tested by:      bdragon
    Fixes:          c86af2cc4cd1 ("imgact_elf: Check note body sizes")
    MFC after:      3 days

 sys/kern/imgact_elf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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