On Fri, Aug 07, 2020 at 11:12:29AM -0700, Nick Desaulniers wrote: > On Fri, Jul 31, 2020 at 4:08 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > > > From: Arvind Sankar <nivedita@xxxxxxxxxxxx> > > > > The BFD linker generates run-time relocations for z_input_len and > > z_output_len, even though they are absolute symbols. > > > > This is fixed for binutils-2.35 [1]. Work around this for earlier > > versions by defining two variables input_len and output_len in addition > > to the symbols, and use them via position-independent references. > > > > This eliminates the last two run-time relocations in the head code and > > allows us to drop the -z noreloc-overflow flag to the linker. > > > > Move the -pie and --no-dynamic-linker LDFLAGS to LDFLAGS_vmlinux instead > > of KBUILD_LDFLAGS. There shouldn't be anything else getting linked, but > > this is the more logical location for these flags, and modversions might > > call the linker if an EXPORT_SYMBOL is left over accidentally in one of > > the decompressors. > > > > [1] https://sourceware.org/bugzilla/show_bug.cgi?id=25754 > > > > Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > > Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx> > > Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> > > Signed-off-by: Arvind Sankar <nivedita@xxxxxxxxxxxx> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > arch/x86/boot/compressed/Makefile | 12 ++---------- > > arch/x86/boot/compressed/head_32.S | 17 ++++++++--------- > > arch/x86/boot/compressed/head_64.S | 4 ++-- > > arch/x86/boot/compressed/mkpiggy.c | 6 ++++++ > > 4 files changed, 18 insertions(+), 21 deletions(-) > > > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile > > index 489fea16bcfb..7db0102a573d 100644 > > --- a/arch/x86/boot/compressed/Makefile > > +++ b/arch/x86/boot/compressed/Makefile > > @@ -51,16 +51,8 @@ UBSAN_SANITIZE :=n > > KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE) > > # Compressed kernel should be built as PIE since it may be loaded at any > > # address by the bootloader. > > -ifeq ($(CONFIG_X86_32),y) > > -KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker) > > -else > > -# To build 64-bit compressed kernel as PIE, we disable relocation > > -# overflow check to avoid relocation overflow error with a new linker > > -# command-line option, -z noreloc-overflow. > > -KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \ > > - && echo "-z noreloc-overflow -pie --no-dynamic-linker") > > -endif > > -LDFLAGS_vmlinux := -T > > +LDFLAGS_vmlinux := $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker) > > Oh, do these still need ld-option? bfd and lld both support these > flags. (Though in their --help, they mention single hyphen and double > hyphen respectively. Also, if we don't build this as PIE because the > linker doesn't support the option, we probably want to fail the build? > The check for pie doesn't, it's dropped in the next patch and pie is used unconditionally. no-dynamic-linker still needs the check as it was only supported from binutils-2.26.
