[Bug ld/24322] New: ld -z shstk sometimes sets IBT property even if -z ibt is not passed

[bonzini at gnu dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=24322

            Bug ID: 24322
           Summary: ld -z shstk sometimes sets IBT property even if -z ibt
                    is not passed
           Product: binutils
           Version: 2.31
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: bonzini at gnu dot org
  Target Milestone: ---

Reproducer

cat > f.s <<\EOF
        .text
        .global _start
_start:
        xor %edi, %edi
        mov $60, %eax
        syscall
EOF
cat > g.s <<\EOF
        .text
        .global main
main:
        xor %edi, %edi
        mov $60, %eax
        syscall
EOF
cat > Makefile <<\EOF
all: f g
f: f.o; ld -o $@ $< -z shstk
g: g.o; gcc -o $@ $< -Wl,-z,shstk

f.o: f.s
g.o: g.s
.s.o:; as --64 -o $@ $<

.PHONY: all
EOF


Now:

$ make
as --64 -o f.o f.s
ld -o f f.o -z shstk
as --64 -o g.o g.s
gcc -o g g.o -Wl,-z,shstk

$ readelf -n f                     # correct
Displaying notes found in: .note.gnu.property
  Owner                 Data size       Description
  GNU                  0x00000010       NT_GNU_PROPERTY_TYPE_0
      Properties: x86 feature: SHSTK

$ readelf -n g                    # wrong
Displaying notes found in: .note.gnu.property
  Owner                 Data size       Description
  GNU                  0x00000010       NT_GNU_PROPERTY_TYPE_0
      Properties: x86 feature: IBT, SHSTK

and indeed running "g" on a machine with CET fails with a segv at the beginning
of "main" (it works if you add the endbr64 hint).

More information:

- the minimal ld command line that causes the bug and still allows "g" to build
is

  /usr/bin/ld --no-add-needed \
    -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o g \
    /usr/lib64/crt1.o /usr/lib64/crti.o g.o -z shstk \
    -L/lib64 -lc

- the minimal ld command line that causes the bug (but does not build a
runnable executable) is

  /usr/bin/ld --no-add-needed -r -o h \
    /usr/lib64/crt1.o /usr/lib64/crti.o g.o -z shstk

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