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Link with -z defs by default (#1535422)

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This commit is contained in:
Florian Weimer 2018-01-22 16:01:54 +01:00
parent 75a53b7ea3
commit 078af19261
3 changed files with 30 additions and 2 deletions
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19
buildflags.md
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@ -59,6 +59,20 @@ position-dependent (no full ASLR) and use lazy binding.
This turns off watermarking, making it impossible to do full hardening
coverage analysis for any binaries produced.
### Disable strict symbol checks in the link editor (ld)
By default, the link editor will refuse to link shared objects which
contain undefined symbols. In some cases (such as when a DSO is
loaded as a plugin and is expected to bind to symbols in the main
executable), undefined symbols are expected. In this case, you can
add
%undefine _strict_symbol_defs_build
to the RPM spec file to disable these strict checks. Alternatively,
you can pass `-z undefs` to ld (written as `-Wl,-z,undefs` on the gcc
command line). The latter needs binutils 2.29.1-12.fc28 or later.
# Individual compiler flags
Compiler flags end up in the environment variables `CFLAGS`,
@ -213,6 +227,11 @@ to the compiler driver `gcc`, and not directly to the link editor
dynamic linker is instructed to revoke write permissions after
dynamic linking. Full protection of relocation data requires the
`-z now` flag (see below).
* `-z defs`: Refuse to link shared objects (DSOs) with undefined symbols.
Such symbols lack symbol versioning information and can be bound to
the wrong (compatibility) symbol version at run time, and not the
actual (default) symbol version which would have been used if the
symbol definition had been available and static link time.
For hardened builds, the
`-specs=/usr/lib/rpm/redhat/redhat-hardened-ld` flag is added to the

8
macros
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@ -166,13 +166,19 @@
%_annotated_build 1
%_annotated_cflags %{?_annotated_build:%{_annobin_cflags}}
# Fail linking if there are undefined symbols. Required for proper
# ELF symbol versioning support.
# Use %undefine _strict_symbol_defs_build" to disable.
%_strict_symbol_defs_build 1
%_ld_symbols_flags %{?_strict_symbol_defs_build:-Wl,-z,defs}
%__global_compiler_flags -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches %{_hardened_cflags} %{_annotated_cflags}
%__global_cflags %{optflags}
%__global_cxxflags %{optflags}
%__global_fflags %{optflags} -I%_fmoddir
%__global_fcflags %{optflags} -I%_fmoddir
%__global_ldflags -Wl,-z,relro %{_hardened_ldflags}
%__global_ldflags -Wl,-z,relro %{_ld_symbols_flags} %{_hardened_ldflags}
#==============================================================================
# ---- Generic auto req/prov filtering macros

5
redhat-rpm-config.spec
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@ -6,7 +6,7 @@
Summary: Red Hat specific rpm configuration files
Name: redhat-rpm-config
Version: 83
Version: 84
Release: 1%{?dist}
# No version specified.
License: GPL+
@ -157,6 +157,9 @@ install -p -m 755 -t %{buildroot}%{_rpmconfigdir} kmod.prov
%{_rpmconfigdir}/macros.d/macros.kmp
%changelog
* Mon Jan 22 2018 Florian Weimer <fweimer@redhat.com> - 84-1
- Link with -z defs by default (#1535422)
* Mon Jan 22 2018 Florian Weimer <fweimer@redhat.com> - 83-1
- Make armhfp flags consistent with GCC defaults