[PATCH v4] x86, boot: Make data from decompress_kernel stage live longer

From: Yinghai Lu
Date: Sun Mar 15 2015 - 03:50:27 EST

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After commit f47233c2d34f ("x86/mm/ASLR: Propagate base load address
calculation"), get warning about setup_data from debugfs for setup_data.
Boris found setup_data for kaslr from boot stage become all 0's in kernel stage.

Current there is overlapping between data section for decompress code and final
kernel running code.

We need to avoid overlapping to make data live longer and to get the passed
properly.

Current code is using extract_offset to control copied kernel position, it
will put the copied kernel in the middle of buffer when kernel run size is
bigger then decompressed needed buffer size. That cause the overlapping.

Detail flow in current code:
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 done, VO use most part buffer from start.
and ZO code and data section will overlap with VO bss section.
And later VO/clear_bss() clear them before code in arch/x86/kernel/setup.c
try to access them.
Current layout:
when init_size is the same as kernel run_size:
run_size
0 extract_offset init_size
|------------------|------------------------|
VO text/data VO bss/brk
input ZO text ZO data

This patch try to:
At first, move ZO to the end of buffer instead of middle of the buffer.
When init_size is bigger than kernel run size. like

0 run_size init_size
|--------------------------------|----------|
VO text/data VO bss/brk
input ZO text ZO data

We already have init_size the buffer size, we can find the end easily.

Secondly, add extra size (ZO data size) to init_size. That is for
even old init_size is same as kernel run size.

run_size
0 old init_size init_size
|------------------------------------------|--------|
VO text/data VO bss/brk
input ZO text ZO data

Here the size changes when old init_size is same as kernel run_size.
# size arch/x86/boot/compressed/vmlinux
text data bss dec hex filename
13247288 264 49248 13296800 cae4a0 arch/x86/boot/compressed/vmlinux
# bootloader reported init_size
kernel: [13cc00000, 13ff8efff]

After patch:
#size arch/x86/boot/compressed/vmlinux
text data bss dec hex filename
13247289 264 49248 13296801 cae4a1 arch/x86/boot/compressed/vmlinux
# bootloader reported init_size
kernel: [13cc00000, 13ffa2fff]

so init_size increase 20 pages 80k.

Fixes: f47233c2d34f ("x86/mm/ASLR: Propagate base load address calculation")
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Matt Fleming <matt.fleming@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>

---
-v2: increase init_size in arch/x86/boot/header.S instead of BRK.
so we can avoid guessing decompressor size.
-v4: add extra checking when ZO_INIT_SIZE>VO_INIT_SIZE, only need
add the difference to cover ADD_ZO

---
arch/x86/boot/Makefile | 2 +-
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 | 2 ++
arch/x86/boot/header.S | 14 ++++++++++++--
arch/x86/kernel/asm-offsets.c | 1 +
arch/x86/kernel/vmlinux.lds.S | 1 +
8 files changed, 34 insertions(+), 12 deletions(-)

Index: linux-2.6/arch/x86/boot/compressed/head_64.S
===================================================================
--- linux-2.6.orig/arch/x86/boot/compressed/head_64.S
+++ linux-2.6/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
Index: linux-2.6/arch/x86/kernel/asm-offsets.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/asm-offsets.c
+++ linux-2.6/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);

Index: linux-2.6/arch/x86/boot/compressed/head_32.S
===================================================================
--- linux-2.6.orig/arch/x86/boot/compressed/head_32.S
+++ linux-2.6/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
@@ -209,8 +211,13 @@ relocated:
/* push arguments for decompress_kernel: */
pushl $z_run_size /* size of kernel with .bss and .brk */
pushl $z_output_len /* decompressed length, end of relocs */
- 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 */
Index: linux-2.6/arch/x86/boot/compressed/mkpiggy.c
===================================================================
--- linux-2.6.orig/arch/x86/boot/compressed/mkpiggy.c
+++ linux-2.6/arch/x86/boot/compressed/mkpiggy.c
@@ -83,11 +83,8 @@ 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 z_run_size\n");
printf("z_run_size = %lu\n", run_size);

Index: linux-2.6/arch/x86/boot/header.S
===================================================================
--- linux-2.6.orig/arch/x86/boot/header.S
+++ linux-2.6/arch/x86/boot/header.S
@@ -440,12 +440,22 @@ setup_data: .quad 0 # 64-bit physical

pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr

-#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset)
+# don't overlap data area of ZO with VO
+#define ADDON_ZO_SIZE (ZO__end - ZO__rodata)
+
+#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
+
+/* only add the difference to cover ADDON_ZO */
+#if (ZO_INIT_SIZE - VO_INIT_SIZE) < ADDON_ZO_SIZE
+#define INIT_SIZE (ZO_INIT_SIZE + (ADDON_ZO_SIZE-(ZO_INIT_SIZE - VO_INIT_SIZE)))
+#else
#define INIT_SIZE ZO_INIT_SIZE
+#endif
+
#else
-#define INIT_SIZE VO_INIT_SIZE
+#define INIT_SIZE (VO_INIT_SIZE + ADDON_ZO_SIZE)
#endif
init_size: .long INIT_SIZE # kernel initialization size
handover_offset: .long 0 # Filled in by build.c
Index: linux-2.6/arch/x86/boot/compressed/vmlinux.lds.S
===================================================================
--- linux-2.6.orig/arch/x86/boot/compressed/vmlinux.lds.S
+++ linux-2.6/arch/x86/boot/compressed/vmlinux.lds.S
@@ -35,6 +35,7 @@ SECTIONS
*(.text.*)
_etext = . ;
}
+ . = ALIGN(PAGE_SIZE); /* keep ADDON_ZO_SIZE page aligned */
.rodata : {
_rodata = . ;
*(.rodata) /* read-only data */
@@ -70,5 +71,6 @@ SECTIONS
_epgtable = . ;
}
#endif
+ . = ALIGN(PAGE_SIZE); /* keep ZO size page aligned */
_end = .;
}
Index: linux-2.6/arch/x86/kernel/vmlinux.lds.S
===================================================================
--- linux-2.6.orig/arch/x86/kernel/vmlinux.lds.S
+++ linux-2.6/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
Index: linux-2.6/arch/x86/boot/Makefile
===================================================================
--- linux-2.6.orig/arch/x86/boot/Makefile
+++ linux-2.6/arch/x86/boot/Makefile
@@ -86,7 +86,7 @@ targets += voffset.h
$(obj)/voffset.h: vmlinux FORCE
$(call if_changed,voffset)

-sed-zoffset := -e 's/^$[0-9a-fA-F]*$ [ABCDGRSTVW] $startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|input_data\|_end\|z_.*$$$/\#define ZO_\2 0x\1/p'
+sed-zoffset := -e 's/^$[0-9a-fA-F]*$ [ABCDGRSTVW] $startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|input_data\|_end\|_rodata\|z_.*$$$/\#define ZO_\2 0x\1/p'

quiet_cmd_zoffset = ZOFFSET $@
cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@
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Next message: Willy Tarreau: "Re: [PATCH v3] staging: panel: change struct bits to a bit array"
Previous message: Yinghai Lu: "[PATCH v4] x86, kaslr: Access the correct kaslr_enabled variable"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]