Commit 3f086189 authored by Arvind Sankar's avatar Arvind Sankar Committed by Ingo Molnar
Browse files

x86/boot: Remove run-time relocations from head_{32,64}.S 

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



Signed-off-by: default avatarArvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarFangrui Song <maskray@google.com>
Link: https://lore.kernel.org/r/20200731230820.1742553-7-keescook@chromium.org
parent a2c4fc4d

arch/x86/boot/compressed/Makefile

+2 −10
Original line number Diff line number Diff line
@@ -52,16 +52,8 @@ 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)

LDFLAGS_vmlinux += -T



hostprogs	:= mkpiggy

HOST_EXTRACFLAGS += -I$(srctree)/tools/include

arch/x86/boot/compressed/head_32.S

+8 −9
Original line number Diff line number Diff line
@@ -179,11 +179,10 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 
 * Do the extraction, and jump to the new kernel..

 */

	/* push arguments for extract_kernel: */

	pushl	$z_output_len	/* decompressed length, end of relocs */



	pushl	output_len@GOTOFF(%ebx)	/* decompressed length, end of relocs */

	pushl	%ebp			/* output address */



	pushl	$z_input_len	/* input_len */

	pushl	input_len@GOTOFF(%ebx)	/* input_len */

	leal	input_data@GOTOFF(%ebx), %eax

	pushl	%eax			/* input_data */

	leal	boot_heap@GOTOFF(%ebx), %eax

arch/x86/boot/compressed/head_64.S

+2 −2
Original line number Diff line number Diff line
@@ -534,9 +534,9 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 
	movq	%rsi, %rdi		/* real mode address */

	leaq	boot_heap(%rip), %rsi	/* malloc area for uncompression */

	leaq	input_data(%rip), %rdx  /* input_data */

	movl	$z_input_len, %ecx	/* input_len */

	movl	input_len(%rip), %ecx	/* input_len */

	movq	%rbp, %r8		/* output target address */

	movl	$z_output_len, %r9d	/* decompressed length, end of relocs */

	movl	output_len(%rip), %r9d	/* decompressed length, end of relocs */

	call	extract_kernel		/* returns kernel location in %rax */

	popq	%rsi

arch/x86/boot/compressed/mkpiggy.c

+6 −0
Original line number Diff line number Diff line
@@ -60,6 +60,12 @@ int main(int argc, char *argv[]) 
	printf(".incbin \"%s\"\n", argv[1]);

	printf("input_data_end:\n");



	printf(".section \".rodata\",\"a\",@progbits\n");

	printf(".globl input_len\n");

	printf("input_len:\n\t.long %lu\n", ilen);

	printf(".globl output_len\n");

	printf("output_len:\n\t.long %lu\n", (unsigned long)olen);



	retval = 0;

bail:

	if (f)