Messages in this thread Patch in this message | | | From | David Gow <> | Date | Thu, 22 Sep 2022 12:42:58 +0800 | Subject | Re: [PATCH v2] arch: um: Mark the stack non-executable to fix a binutils warning |
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On Thu, Sep 22, 2022 at 1:47 AM 'Nick Desaulniers' via KUnit Development <kunit-dev@googlegroups.com> wrote: > > On Tue, Sep 20, 2022 at 11:49 PM David Gow <davidgow@google.com> wrote: > > > > Since binutils 2.39, ld will print a warning if any stack section is > > executable, which is the default for stack sections on files without a > > .note.GNU-stack section. > > > > This was fixed for x86 in commit ffcf9c5700e4 ("x86: link vdso and boot with -z noexecstack --no-warn-rwx-segments"), > > but remained broken for UML, resulting in several warnings: > > > > /usr/bin/ld: warning: arch/x86/um/vdso/vdso.o: missing .note.GNU-stack section implies executable stack > > /usr/bin/ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker > > /usr/bin/ld: warning: .tmp_vmlinux.kallsyms1 has a LOAD segment with RWX permissions > > /usr/bin/ld: warning: .tmp_vmlinux.kallsyms1.o: missing .note.GNU-stack section implies executable stack > > /usr/bin/ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker > > /usr/bin/ld: warning: .tmp_vmlinux.kallsyms2 has a LOAD segment with RWX permissions > > /usr/bin/ld: warning: .tmp_vmlinux.kallsyms2.o: missing .note.GNU-stack section implies executable stack > > /usr/bin/ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker > > /usr/bin/ld: warning: vmlinux has a LOAD segment with RWX permissions > > > > Link both the VDSO and vmlinux with -z noexecstack, fixing the warnings > > about .note.GNU-stack sections. In addition, pass --no-warn-rwx-segments > > to dodge the remaining warnings about LOAD segments with RWX permissions > > in the kallsyms objects. (Note that this flag is apparently not > > available on lld, so hide it behind a test for BFD, which is what the > > x86 patch does.) > > > > Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ffcf9c5700e49c0aee42dcba9a12ba21338e8136 > > Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107 > > Signed-off-by: David Gow <davidgow@google.com> > > Reviewed-by: Lukas Straub <lukasstraub2@web.de> > > Tested-by: Lukas Straub <lukasstraub2@web.de> > > Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested > > --- > > > > Note that this still doesn't seem to be working properly with make > > LLVM=1. It doesn't appear to break anything, and still is an improvement > > for gcc, so seems worthwhile anyway... > > Hi David, > Do you have more info about this comment? Perhaps there's more > hermiticity issues with ARCH=um when a linker is explicitly specified > via LD= or HOSTLD=, or implied via LLVM=1. > > Looking at our CI for ARCH=um builds... > https://github.com/ClangBuiltLinux/continuous-integration2/actions/runs/3095779516/jobs/5012260390 > warnings from /usr/bin/ld. That's...unexpected. > I've filed https://github.com/ClangBuiltLinux/linux/issues/1715 to > follow up on this. >
Thanks for following up on this.
Yeah: what I'm seeing seems to match it does look like ld is being used instead of lld.
I tried -fuse-ld=lld via the following patch, though, and got a whole bunch of "error: relocation R_X86_64_64 cannot be used against local symbol; recompile with -fPIC" errors, so I think there's probably more issues with UML and LLD that need working out. (I had no luck with CONFIG_STATIC_LINK=y, nor with an attempt to use $(LD) directly, instead of via $(CC)).
--- diff --git a/arch/um/Makefile b/arch/um/Makefile index f1d4d67157be..01d9eae736be 100644 --- a/arch/um/Makefile +++ b/arch/um/Makefile @@ -139,6 +139,9 @@ ifeq ($(CONFIG_LD_IS_BFD),y) LDFLAGS_EXECSTACK += $(call ld-option,--no-warn-rwx-segments) endif
+# Since we're using CC as the driver, we need to force LLD if it is requested. +LINK-$(CONFIG_LD_IS_LLD) += $(call cc-option,--ld-path=$(LD),-fuse-ld=lld) + LD_FLAGS_CMDLINE = $(foreach opt,$(KBUILD_LDFLAGS),-Wl,$(opt))
# Used by link-vmlinux.sh which has special support for um link
---
I'll update the GitHub issue with these notes as well, but I definitely think it'd be best not to make UML use lld here until it actually builds something: even with the warnings, ld is at least latting us run at all.
Cheers, -- David > > > > Changes since v1: > > http://lists.infradead.org/pipermail/linux-um/2022-August/004234.html > > - Pass the -z noexecstack and --no-warn-rwx-segments flags as LDFLAGS, > > rather than as CFLAGS via -Wl > > - Check that --no-warn-rwx-segments exists with the ld-option function > > (Thanks Richard) > > - Add Lukas and Randy's tags. > > > > > > arch/um/Makefile | 8 ++++++++ > > arch/x86/um/vdso/Makefile | 2 +- > > 2 files changed, 9 insertions(+), 1 deletion(-) > > > > diff --git a/arch/um/Makefile b/arch/um/Makefile > > index f2fe63bfd819..f1d4d67157be 100644 > > --- a/arch/um/Makefile > > +++ b/arch/um/Makefile > > @@ -132,10 +132,18 @@ export LDS_ELF_FORMAT := $(ELF_FORMAT) > > # The wrappers will select whether using "malloc" or the kernel allocator. > > LINK_WRAPS = -Wl,--wrap,malloc -Wl,--wrap,free -Wl,--wrap,calloc > > > > +# Avoid binutils 2.39+ warnings by marking the stack non-executable and > > +# ignorning warnings for the kallsyms sections. > > +LDFLAGS_EXECSTACK = -z noexecstack > > +ifeq ($(CONFIG_LD_IS_BFD),y) > > +LDFLAGS_EXECSTACK += $(call ld-option,--no-warn-rwx-segments) > > +endif > > + > > LD_FLAGS_CMDLINE = $(foreach opt,$(KBUILD_LDFLAGS),-Wl,$(opt)) > > > > # Used by link-vmlinux.sh which has special support for um link > > export CFLAGS_vmlinux := $(LINK-y) $(LINK_WRAPS) $(LD_FLAGS_CMDLINE) > > +export LDFLAGS_vmlinux := $(LDFLAGS_EXECSTACK) > > > > # When cleaning we don't include .config, so we don't include > > # TT or skas makefiles and don't clean skas_ptregs.h. > > diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile > > index 8c0396fd0e6f..6fbe97c52c99 100644 > > --- a/arch/x86/um/vdso/Makefile > > +++ b/arch/x86/um/vdso/Makefile > > @@ -65,7 +65,7 @@ quiet_cmd_vdso = VDSO $@ > > -Wl,-T,$(filter %.lds,$^) $(filter %.o,$^) && \ > > sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@' > > > > -VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv > > +VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv -z noexecstack > > GCOV_PROFILE := n > > > > # > > -- > > 2.37.3.968.ga6b4b080e4-goog > > > > > -- > Thanks, > ~Nick Desaulniers > > -- > You received this message because you are subscribed to the Google Groups "KUnit Development" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kunit-dev+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/kunit-dev/CAKwvOdnLaDn%3DEfGFhjhcZe4EzvjU7Cws3z3KjLGwW%3DxnqnmHyw%40mail.gmail.com. [unhandled content-type:application/pkcs7-signature] | |