[PATCH v3 2/7] x86, boot: Move ZO to end of buffer

Yinghai Lu
2015-03-07T22:07:16Z

Boris found data from boot stage can not be used kernel stage.

Bootloader allocate buffer according to init_size in hdr, and load the
ZO (arch/x86/boot/compressed/vmlinux) from start of that buffer.
During running of ZO, ZO move itself to the middle of buffer at
z_extract_offset to make sure that decompressor would not have output
overwrite input data before input data get consumed.
After decompressor is called, VO (vmlinux) use whole buffer from start,
and ZO code and data section is overlapped with VO bss section.
And later VO/clear_bss() clear them before code in arch/x86/kernel/setup.c
access them.

To make the data survive that later, we should avoid the overlapping.
At first move ZO close the end of buffer instead of middle of the buffer,
that will move out ZO data out of VO bss area.

Also after that we can find out where is data section of copied ZO
instead of guessing. That will aslr mem_avoid array filling for
new buffer seaching much simple.

And rename z_extract_offset to z_min_extract_offset, as it is
actually the minimum offset for extracting now.

To keep the final real extract_offset to be page aligned like
min_extract_offset, we need make VO _end and ZO _end both
page aligned to make sure init_size always page aligned.

Next patch will add ZO data size to init_size, so it will make sure
ZO data is even out of VO brk area.

Fixes: f47233c2d34f ("x86/mm/ASLR: Propagate base load address calculation")
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
---
arch/x86/boot/compressed/head_32.S | 11 +++++++++--
arch/x86/boot/compressed/head_64.S | 8 ++++++--
arch/x86/boot/compressed/mkpiggy.c | 7 ++-----
arch/x86/boot/compressed/vmlinux.lds.S | 1 +
arch/x86/boot/header.S | 2 +-
arch/x86/kernel/asm-offsets.c | 1 +
arch/x86/kernel/vmlinux.lds.S | 1 +
7 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index cbed140..a9b56f1 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -147,7 +147,9 @@ preferred_addr:
1:

/* Target address to relocate to for decompression */
- addl $z_extract_offset, %ebx
+ movl BP_init_size(%esi), %eax
+ subl $_end, %eax
+ addl %eax, %ebx

/* Set up the stack */
leal boot_stack_end(%ebx), %esp
@@ -208,8 +210,13 @@ relocated:
*/
/* push arguments for decompress_kernel: */
pushl $z_output_len /* decompressed length */
- leal z_extract_offset_negative(%ebx), %ebp
+
+ movl BP_init_size(%esi), %eax
+ subl $_end, %eax
+ movl %ebx, %ebp
+ subl %eax, %ebp
pushl %ebp /* output address */
+
pushl $z_input_len /* input_len */
leal input_data(%ebx), %eax
pushl %eax /* input_data */
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 2884e0c..69015b5 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -101,7 +101,9 @@ ENTRY(startup_32)
1:

/* Target address to relocate to for decompression */
- addl $z_extract_offset, %ebx
+ movl BP_init_size(%esi), %eax
+ subl $_end, %eax
+ addl %eax, %ebx

/*
* Prepare for entering 64 bit mode
@@ -329,7 +331,9 @@ preferred_addr:
1:

/* Target address to relocate to for decompression */
- leaq z_extract_offset(%rbp), %rbx
+ movl BP_init_size(%rsi), %ebx
+ subl $_end, %ebx
+ addq %rbp, %rbx

/* Set up the stack */
leaq boot_stack_end(%rbx), %rsp
diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c
index b669ab6..c03b009 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -80,11 +80,8 @@ int main(int argc, char *argv[])
printf("z_input_len = %lu\n", ilen);
printf(".globl z_output_len\n");
printf("z_output_len = %lu\n", (unsigned long)olen);
- printf(".globl z_extract_offset\n");
- printf("z_extract_offset = 0x%lx\n", offs);
- /* z_extract_offset_negative allows simplification of head_32.S */
- printf(".globl z_extract_offset_negative\n");
- printf("z_extract_offset_negative = -0x%lx\n", offs);
+ printf(".globl z_min_extract_offset\n");
+ printf("z_min_extract_offset = 0x%lx\n", offs);

printf(".globl input_data, input_data_end\n");
printf("input_data:\n");
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 34d047c..e24e0a0 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -70,5 +70,6 @@ SECTIONS
_epgtable = . ;
}
#endif
+ . = ALIGN(PAGE_SIZE); /* keep ZO size page aligned */
_end = .;
}
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 16ef025..9bfab22 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -440,7 +440,7 @@ setup_data: .quad 0 # 64-bit physical pointer to

pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr

-#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset)
+#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_min_extract_offset)
#define VO_INIT_SIZE (VO__end - VO__text)
#if ZO_INIT_SIZE > VO_INIT_SIZE
#define INIT_SIZE ZO_INIT_SIZE
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 9f6b934..0e8e4f7 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -66,6 +66,7 @@ void common(void) {
OFFSET(BP_hardware_subarch, boot_params, hdr.hardware_subarch);
OFFSET(BP_version, boot_params, hdr.version);
OFFSET(BP_kernel_alignment, boot_params, hdr.kernel_alignment);
+ OFFSET(BP_init_size, boot_params, hdr.init_size);
OFFSET(BP_pref_address, boot_params, hdr.pref_address);
OFFSET(BP_code32_start, boot_params, hdr.code32_start);

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 00bf300..ac25c7f 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -325,6 +325,7 @@ SECTIONS
__brk_limit = .;
}

+ . = ALIGN(PAGE_SIZE); /* keep VO init size page aligned */
_end = .;

STABS_DEBUG
--
1.8.4.5