arm64: relocatable: fix inconsistencies in linker script and options

commit 3bbd3db86470c701091fb1d67f1fab6621debf50 upstream.

readelf complains about the section layout of vmlinux when building
with CONFIG_RELOCATABLE=y (for KASLR):

  readelf: Warning: [21]: Link field (0) should index a symtab section.
  readelf: Warning: [21]: Info field (0) should index a relocatable section.

Also, it seems that our use of '-pie -shared' is contradictory, and
thus ambiguous. In general, the way KASLR is wired up at the moment
is highly tailored to how ld.bfd happens to implement (and conflate)
PIE executables and shared libraries, so given the current effort to
support other toolchains, let's fix some of these issues as well.

- Drop the -pie linker argument and just leave -shared. In ld.bfd,
  the differences between them are unclear (except for the ELF type
  of the produced image [0]) but lld chokes on seeing both at the
  same time.

- Rename the .rela output section to .rela.dyn, as is customary for
  shared libraries and PIE executables, so that it is not misidentified
  by readelf as a static relocation section (producing the warnings
  above).

- Pass the -z notext and -z norelro options to explicitly instruct the
  linker to permit text relocations, and to omit the RELRO program
  header (which requires a certain section layout that we don't adhere
  to in the kernel). These are the defaults for current versions of
  ld.bfd.

- Discard .eh_frame and .gnu.hash sections to avoid them from being
  emitted between .head.text and .text, screwing up the section layout.

These changes only affect the ELF image, and produce the same binary
image.

[0] b9dce7f1ba01 ("arm64: kernel: force ET_DYN ELF type for ...")

Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Smith <peter.smith@linaro.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 48f2b3657507c30eb335bece261a51ee7bf6125e..0c5f70e6d5cfae83aad0c9bba2c2a8607b02e3d4 100644 (file)
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -18,7 +18,7 @@ ifeq ($(CONFIG_RELOCATABLE), y)
 # Pass --no-apply-dynamic-relocs to restore pre-binutils-2.27 behaviour
 # for relative relocs, since this leads to better Image compression
 # with the relocation offsets always being zero.
-LDFLAGS_vmlinux                += -pie -shared -Bsymbolic \
+LDFLAGS_vmlinux                += -shared -Bsymbolic -z notext -z norelro \
                        $(call ld-option, --no-apply-dynamic-relocs)
 endif
 

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index ddfd3c0942f7acf27d3bb0396ebbd3ba87303296..6edfdf5b061d6fbb96860cbc1590e6c6a4ce8a56 100644 (file)
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -99,7 +99,8 @@ SECTIONS
                *(.discard)
                *(.discard.*)
                *(.interp .dynamic)
-               *(.dynsym .dynstr .hash)
+               *(.dynsym .dynstr .hash .gnu.hash)
+               *(.eh_frame)
        }
 
        . = KIMAGE_VADDR + TEXT_OFFSET;
@@ -176,12 +177,12 @@ SECTIONS
 
        PERCPU_SECTION(L1_CACHE_BYTES)
 
-       .rela : ALIGN(8) {
+       .rela.dyn : ALIGN(8) {
                *(.rela .rela*)
        }
 
-       __rela_offset   = ABSOLUTE(ADDR(.rela) - KIMAGE_VADDR);
-       __rela_size     = SIZEOF(.rela);
+       __rela_offset   = ABSOLUTE(ADDR(.rela.dyn) - KIMAGE_VADDR);
+       __rela_size     = SIZEOF(.rela.dyn);
 
        . = ALIGN(SEGMENT_ALIGN);
        __initdata_end = .;