linux/arch/x86/boot
Arvind Sankar 5214028dd8 x86/boot: Correct relocation destination on old linkers
For the 32-bit kernel, as described in

  6d92bc9d48 ("x86/build: Build compressed x86 kernels as PIE"),

pre-2.26 binutils generates R_386_32 relocations in PIE mode. Since the
startup code does not perform relocation, any reloc entry with R_386_32
will remain as 0 in the executing code.

Commit

  974f221c84 ("x86/boot: Move compressed kernel to the end of the
                 decompression buffer")

added a new symbol _end but did not mark it hidden, which doesn't give
the correct offset on older linkers. This causes the compressed kernel
to be copied beyond the end of the decompression buffer, rather than
flush against it. This region of memory may be reserved or already
allocated for other purposes by the bootloader.

Mark _end as hidden to fix. This changes the relocation from R_386_32 to
R_386_RELATIVE even on the pre-2.26 binutils.

For 64-bit, this is not strictly necessary, as the 64-bit kernel is only
built as PIE if the linker supports -z noreloc-overflow, which implies
binutils-2.27+, but for consistency, mark _end as hidden here too.

The below illustrates the before/after impact of the patch using
binutils-2.25 and gcc-4.6.4 (locally compiled from source) and QEMU.

  Disassembly before patch:
    48:   8b 86 60 02 00 00       mov    0x260(%esi),%eax
    4e:   2d 00 00 00 00          sub    $0x0,%eax
                          4f: R_386_32    _end
  Disassembly after patch:
    48:   8b 86 60 02 00 00       mov    0x260(%esi),%eax
    4e:   2d 00 f0 76 00          sub    $0x76f000,%eax
                          4f: R_386_RELATIVE      *ABS*

Dump from extract_kernel before patch:
	early console in extract_kernel
	input_data: 0x0207c098 <--- this is at output + init_size
	input_len: 0x0074fef1
	output: 0x01000000
	output_len: 0x00fa63d0
	kernel_total_size: 0x0107c000
	needed_size: 0x0107c000

Dump from extract_kernel after patch:
	early console in extract_kernel
	input_data: 0x0190d098 <--- this is at output + init_size - _end
	input_len: 0x0074fef1
	output: 0x01000000
	output_len: 0x00fa63d0
	kernel_total_size: 0x0107c000
	needed_size: 0x0107c000

Fixes: 974f221c84 ("x86/boot: Move compressed kernel to the end of the decompression buffer")
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200207214926.3564079-1-nivedita@alum.mit.edu
2020-05-19 14:11:22 +02:00
..
compressed x86/boot: Correct relocation destination on old linkers 2020-05-19 14:11:22 +02:00
tools SPDX patches for 5.7-rc1. 2020-04-03 13:12:26 -07:00
.gitignore .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
a20.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
apm.c x86/boot: Fix comment spelling 2020-03-17 20:52:52 +01:00
bioscall.S treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 83 2019-05-24 17:37:52 +02:00
bitops.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
boot.h x86/boot: Use common BUILD_BUG_ON 2019-08-16 14:15:50 +02:00
cmdline.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
code16gcc.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
copy.S x86/asm: Do not annotate functions with GLOBAL 2019-10-18 11:25:58 +02:00
cpu.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
cpucheck.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
cpuflags.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
cpuflags.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ctype.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
early_serial_console.c x86: Clean up 'sizeof x' => 'sizeof(x)' 2018-10-29 07:13:28 +01:00
edd.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
genimage.sh x86/build: Make isoimage work on Debian 2017-12-16 16:23:31 +01:00
header.S efi/x86: Add kernel preferred address to PE header 2020-03-08 09:58:20 +01:00
install.sh
main.c x86/boot: Use common BUILD_BUG_ON 2019-08-16 14:15:50 +02:00
Makefile Merge branch 'x86-boot-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2020-03-31 10:28:35 -07:00
memory.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
mkcpustr.c x86/cpu: Print VMX flags in /proc/cpuinfo using VMX_FEATURES_* 2020-01-13 18:36:02 +01:00
mtools.conf.in
pm.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
pmjump.S x86/asm: Do not annotate functions with GLOBAL 2019-10-18 11:25:58 +02:00
printf.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
regs.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 83 2019-05-24 17:37:52 +02:00
setup.ld x86/vmlinux: Drop unneeded linker script discard of .eh_frame 2020-02-25 14:51:29 +01:00
string.c x86/boot: Add kstrtoul() from lib/ 2020-05-04 15:19:07 +02:00
string.h x86/boot: Add kstrtoul() from lib/ 2020-05-04 15:19:07 +02:00
tty.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
version.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
vesa.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 48 2019-05-24 17:27:13 +02:00
video-bios.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
video-mode.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
video-vesa.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
video-vga.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
video.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00
video.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 497 2019-06-19 17:09:53 +02:00