lkml.org 
[lkml]   [2020]   [May]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4/4] x86/boot: Check that there are no runtime relocations
Date
Add a linker script check that there are no runtime relocations, and
remove the old one that tries to check via looking for specially-named
sections in the object files.

Drop the tests for -fPIE compiler option and -pie linker option, as they
are available in all supported gcc and binutils versions (as well as
clang and lld).

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
arch/x86/boot/compressed/Makefile | 28 +++-----------------------
arch/x86/boot/compressed/vmlinux.lds.S | 11 ++++++++++
2 files changed, 14 insertions(+), 25 deletions(-)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index d3e882e855ee..679a2b383bfe 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -27,7 +27,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4

KBUILD_CFLAGS := -m$(BITS) -O2
-KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC)
+KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
cflags-$(CONFIG_X86_32) := -march=i386
cflags-$(CONFIG_X86_64) := -mcmodel=small
@@ -49,7 +49,7 @@ UBSAN_SANITIZE :=n
KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
# Compressed kernel should be built as PIE since it may be loaded at any
# address by the bootloader.
-KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
+KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
LDFLAGS_vmlinux := -T

hostprogs := mkpiggy
@@ -84,30 +84,8 @@ vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
vmlinux-objs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o

-# The compressed kernel is built with -fPIC/-fPIE so that a boot loader
-# can place it anywhere in memory and it will still run. However, since
-# it is executed as-is without any ELF relocation processing performed
-# (and has already had all relocation sections stripped from the binary),
-# none of the code can use data relocations (e.g. static assignments of
-# pointer values), since they will be meaningless at runtime. This check
-# will refuse to link the vmlinux if any of these relocations are found.
-quiet_cmd_check_data_rel = DATAREL $@
-define cmd_check_data_rel
- for obj in $(filter %.o,$^); do \
- $(READELF) -S $$obj | grep -qF .rel.local && { \
- echo "error: $$obj has data relocations!" >&2; \
- exit 1; \
- } || true; \
- done
-endef
-
-# We need to run two commands under "if_changed", so merge them into a
-# single invocation.
-quiet_cmd_check-and-link-vmlinux = LD $@
- cmd_check-and-link-vmlinux = $(cmd_check_data_rel); $(cmd_ld)
-
$(obj)/vmlinux: $(vmlinux-objs-y) FORCE
- $(call if_changed,check-and-link-vmlinux)
+ $(call if_changed,ld)

OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
$(obj)/vmlinux.bin: vmlinux FORCE
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index d826ab38a8f9..0ac14feacb24 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -11,9 +11,15 @@ OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT)
#ifdef CONFIG_X86_64
OUTPUT_ARCH(i386:x86-64)
ENTRY(startup_64)
+
+#define REL .rela
+
#else
OUTPUT_ARCH(i386)
ENTRY(startup_32)
+
+#define REL .rel
+
#endif

SECTIONS
@@ -42,6 +48,9 @@ SECTIONS
*(.rodata.*)
_erodata = . ;
}
+ REL.dyn : {
+ *(REL.*)
+ }
.got : {
*(.got)
}
@@ -83,3 +92,5 @@ ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT en
#else
ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!")
#endif
+
+ASSERT(SIZEOF(REL.dyn) == 0, "Unexpected runtime relocations detected!")
--
2.26.2
\
 
 \ /
  Last update: 2020-05-24 23:28    [W:0.210 / U:9.684 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site