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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: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Link: https://lore.kernel.org/r/20200731230820.1742553-7-keescook@chromium.org
This commit is contained in:
Arvind Sankar 2020-07-31 16:07:50 -07:00 committed by Ingo Molnar
parent a2c4fc4d4e
commit 3f086189cd
4 changed files with 18 additions and 21 deletions
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12
arch/x86/boot/compressed/Makefile
View File

@ -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

17
arch/x86/boot/compressed/head_32.S
View File

@ -178,18 +178,17 @@ 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 */
/* push arguments for extract_kernel: */
pushl %ebp /* output address */
pushl $z_input_len /* input_len */
pushl output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */
pushl %ebp /* output address */
pushl input_len@GOTOFF(%ebx) /* input_len */
leal input_data@GOTOFF(%ebx), %eax
pushl %eax /* input_data */
pushl %eax /* input_data */
leal boot_heap@GOTOFF(%ebx), %eax
pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call extract_kernel /* returns kernel location in %eax */
pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call extract_kernel /* returns kernel location in %eax */
addl $24, %esp
/*

4
arch/x86/boot/compressed/head_64.S
View File

@ -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

6
arch/x86/boot/compressed/mkpiggy.c
View File

@ -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)