[PATCH v3 1/7] x86, kaslr: Use init_size instead of run_size

Yinghai Lu
2015-03-07T22:07:15Z

commit e6023367d779 ("x86, kaslr: Prevent .bss from overlaping initrd")
introduced one run_size for kaslr.
We should use real runtime size (include copy/decompress) aka init_size.

run_size is VO (vmlinux) init size include bss and brk.
init_size is the size needed for decompress and it is bigger than run_size
when decompress need more buff.

According to arch/x86/boot/header.S:
| #define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset)
| #define VO_INIT_SIZE (VO__end - VO__text)
| #if ZO_INIT_SIZE > VO_INIT_SIZE
| #define INIT_SIZE ZO_INIT_SIZE
| #else
| #define INIT_SIZE VO_INIT_SIZE
| #endif
| init_size: .long INIT_SIZE # kernel initialization size

Bootloader allocate buffer according to init_size in hdr, and load the
ZO (arch/x86/boot/compressed/vmlinux) from start of that buffer.
init_size first come from VO (vmlinux) init size. That VO init size
is from VO _end to VO _end and include VO bss and brk area.

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.
But z_extract_offset calculating is based on size of VO (vmlinux) and size
of compressed VO only at first.
So need to make sure [z_extra_offset, init_size) will fit ZO, that means
init_size need to be adjusted according to ZO size.
That make init_size is always >= run_size.

During aslr buffer searching, we need to make sure the new buffer is big
enough for decompress at first. So use init_size instead, and kill not
needed run_size related code.

Fixes: e6023367d779 ("x86, kaslr: Prevent .bss from overlaping initrd")
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Junjie Mao <eternal.n08@gmail.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
---
arch/x86/boot/compressed/Makefile | 4 +---
arch/x86/boot/compressed/head_32.S | 5 ++---
arch/x86/boot/compressed/head_64.S | 5 +----
arch/x86/boot/compressed/misc.c | 15 +++++++-------
arch/x86/boot/compressed/mkpiggy.c | 9 ++------
arch/x86/tools/calc_run_size.sh | 42 --------------------------------------
6 files changed, 13 insertions(+), 67 deletions(-)
delete mode 100644 arch/x86/tools/calc_run_size.sh

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 0a291cd..70cc92c 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -92,10 +92,8 @@ suffix-$(CONFIG_KERNEL_XZ) := xz
suffix-$(CONFIG_KERNEL_LZO) := lzo
suffix-$(CONFIG_KERNEL_LZ4) := lz4

-RUN_SIZE = $(shell $(OBJDUMP) -h vmlinux | \
- $(CONFIG_SHELL) $(srctree)/arch/x86/tools/calc_run_size.sh)
quiet_cmd_mkpiggy = MKPIGGY $@
- cmd_mkpiggy = $(obj)/mkpiggy $< $(RUN_SIZE) > $@ || ( rm -f $@ ; false )
+ cmd_mkpiggy = $(obj)/mkpiggy $< > $@ || ( rm -f $@ ; false )

targets += piggy.S
$(obj)/piggy.S: $(obj)/vmlinux.bin.$(suffix-y) $(obj)/mkpiggy FORCE
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 1d7fbbc..cbed140 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -207,8 +207,7 @@ relocated:
* Do the decompression, and jump to the new kernel..
*/
/* 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 */
+ pushl $z_output_len /* decompressed length */
leal z_extract_offset_negative(%ebx), %ebp
pushl %ebp /* output address */
pushl $z_input_len /* input_len */
@@ -218,7 +217,7 @@ relocated:
pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call decompress_kernel /* returns kernel location in %eax */
- addl $28, %esp
+ addl $24, %esp

/*
* Jump to the decompressed kernel.
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 6b1766c..2884e0c 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -402,16 +402,13 @@ relocated:
* Do the decompression, and jump to the new kernel..
*/
pushq %rsi /* Save the real mode argument */
- movq $z_run_size, %r9 /* size of kernel with .bss and .brk */
- pushq %r9
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 */
movq %rbp, %r8 /* output target address */
- movq $z_output_len, %r9 /* decompressed length, end of relocs */
+ movq $z_output_len, %r9 /* decompressed length */
call decompress_kernel /* returns kernel location in %rax */
- popq %r9
popq %rsi

/*
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 5903089..51e9e54 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -370,10 +370,10 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
unsigned char *input_data,
unsigned long input_len,
unsigned char *output,
- unsigned long output_len,
- unsigned long run_size)
+ unsigned long output_len)
{
unsigned char *output_orig = output;
+ unsigned long init_size;

real_mode = rmode;

@@ -396,15 +396,14 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
free_mem_ptr = heap; /* Heap */
free_mem_end_ptr = heap + BOOT_HEAP_SIZE;

+ init_size = real_mode->hdr.init_size;
+
/*
- * The memory hole needed for the kernel is the larger of either
- * the entire decompressed kernel plus relocation table, or the
- * entire decompressed kernel plus .bss and .brk sections.
+ * The memory hole needed for the kernel is init_size for running
+ * and init_size is bigger than output_len always.
*/
output = choose_kernel_location(real_mode, input_data, input_len,
- output,
- output_len > run_size ? output_len
- : run_size);
+ output, init_size);

/* Validate memory location choices. */
if ((unsigned long)output & (MIN_KERNEL_ALIGN - 1))
diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c
index d8222f2..b669ab6 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -36,13 +36,11 @@ int main(int argc, char *argv[])
uint32_t olen;
long ilen;
unsigned long offs;
- unsigned long run_size;
FILE *f = NULL;
int retval = 1;

- if (argc < 3) {
- fprintf(stderr, "Usage: %s compressed_file run_size\n",
- argv[0]);
+ if (argc < 2) {
+ fprintf(stderr, "Usage: %s compressed_file\n", argv[0]);
goto bail;
}

@@ -76,7 +74,6 @@ int main(int argc, char *argv[])
offs += olen >> 12; /* Add 8 bytes for each 32K block */
offs += 64*1024 + 128; /* Add 64K + 128 bytes slack */
offs = (offs+4095) & ~4095; /* Round to a 4K boundary */
- run_size = atoi(argv[2]);

printf(".section \".rodata..compressed\",\"a\",@progbits\n");
printf(".globl z_input_len\n");
@@ -88,8 +85,6 @@ int main(int argc, char *argv[])
/* 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_run_size\n");
- printf("z_run_size = %lu\n", run_size);

printf(".globl input_data, input_data_end\n");
printf("input_data:\n");
diff --git a/arch/x86/tools/calc_run_size.sh b/arch/x86/tools/calc_run_size.sh
deleted file mode 100644
index 1a4c17b..0000000
--- a/arch/x86/tools/calc_run_size.sh
+++ /dev/null
@@ -1,42 +0,0 @@
-#!/bin/sh
-#
-# Calculate the amount of space needed to run the kernel, including room for
-# the .bss and .brk sections.
-#
-# Usage:
-# objdump -h a.out | sh calc_run_size.sh
-
-NUM='\([0-9a-fA-F]*[ \t]*\)'
-OUT=$(sed -n 's/^[ \t0-9]*.b[sr][sk][ \t]*'"$NUM$NUM$NUM$NUM"'.*/\1\4/p')
-if [ -z "$OUT" ] ; then
- echo "Never found .bss or .brk file offset" >&2
- exit 1
-fi
-
-OUT=$(echo ${OUT# })
-sizeA=$(printf "%d" 0x${OUT%% *})
-OUT=${OUT#* }
-offsetA=$(printf "%d" 0x${OUT%% *})
-OUT=${OUT#* }
-sizeB=$(printf "%d" 0x${OUT%% *})
-OUT=${OUT#* }
-offsetB=$(printf "%d" 0x${OUT%% *})
-
-run_size=$(( $offsetA + $sizeA + $sizeB ))
-
-# BFD linker shows the same file offset in ELF.
-if [ "$offsetA" -ne "$offsetB" ] ; then
- # Gold linker shows them as consecutive.
- endB=$(( $offsetB + $sizeB ))
- if [ "$endB" != "$run_size" ] ; then
- printf "sizeA: 0x%x\n" $sizeA >&2
- printf "offsetA: 0x%x\n" $offsetA >&2
- printf "sizeB: 0x%x\n" $sizeB >&2
- printf "offsetB: 0x%x\n" $offsetB >&2
- echo ".bss and .brk are non-contiguous" >&2
- exit 1
- fi
-fi
-
-printf "%d\n" $run_size
-exit 0
--
1.8.4.5