[PATCH] x86, kaslr: Prevent .bss from overlaping initrd
From: Junjie Mao
Date: Thu Oct 30 2014 - 08:43:22 EST
When choosing a random address, the current implementation does not take into
account the reversed space for .bss and .brk sections. Thus the relocated kernel
may overlap other components in memory, e.g. the initrd image:
+-------------------+
| decompressed |
| kernel |
| (relocated) |
+-------------------+--
| | \
+-------------------+ .bss and .brk section
| | /
| initrd |--
| |
+-------------------+
Here is an example of the overlap from a x86_64 kernel in qemu (the ranges of
physical addresses are presented):
compressed kernel: [0x0449626e, 0x04e30aa3]
initrd: [0x13ce6000, 0x13fef373]
relocated kernel: [0x0fe00000, 0x13c1c2bb]
.bss and .brk sections: [0x13c1c2bc, 0x148262bb]
The initrd image will then be overwritten by the memset during early
initialization:
[ 1.655204] Unpacking initramfs...
[ 1.662831] Initramfs unpacking failed: junk in compressed archive
This patch prevents the above situation by requiring a larger space when looking
for a random kernel base, so that existing logic can effectively avoids the
overlap.
Fixes: 82fa9637a2 ("x86, kaslr: Select random position from e820 maps")
Reported-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Signed-off-by: Junjie Mao <eternal.n08@xxxxxxxxx>
---
arch/x86/boot/compressed/Makefile | 3 ++-
arch/x86/boot/compressed/aslr.c | 5 +++--
arch/x86/boot/compressed/head_32.S | 3 ++-
arch/x86/boot/compressed/head_64.S | 3 +++
arch/x86/boot/compressed/misc.c | 6 ++++--
arch/x86/boot/compressed/misc.h | 6 ++++--
arch/x86/boot/compressed/mkpiggy.c | 8 ++++++--
arch/x86/tools/calc_reserved.awk | 21 +++++++++++++++++++++
8 files changed, 45 insertions(+), 10 deletions(-)
create mode 100644 arch/x86/tools/calc_reserved.awk
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 704f58aa79cd..419e12b203d9 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -76,8 +76,9 @@ suffix-$(CONFIG_KERNEL_XZ) := xz
suffix-$(CONFIG_KERNEL_LZO) := lzo
suffix-$(CONFIG_KERNEL_LZ4) := lz4
+RESERVED_SIZE = $(shell objdump -h vmlinux | awk -f $(srctree)/arch/x86/tools/calc_reserved.awk)
quiet_cmd_mkpiggy = MKPIGGY $@
- cmd_mkpiggy = $(obj)/mkpiggy $< > $@ || ( rm -f $@ ; false )
+ cmd_mkpiggy = $(obj)/mkpiggy $< $(RESERVED_SIZE) > $@ || ( rm -f $@ ; false )
targets += piggy.S
$(obj)/piggy.S: $(obj)/vmlinux.bin.$(suffix-y) $(obj)/mkpiggy FORCE
diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index bb1376381985..d4695b022971 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -298,7 +298,8 @@ static unsigned long find_random_addr(unsigned long minimum,
unsigned char *choose_kernel_location(unsigned char *input,
unsigned long input_size,
unsigned char *output,
- unsigned long output_size)
+ unsigned long output_size,
+ unsigned long reserved_size)
{
unsigned long choice = (unsigned long)output;
unsigned long random;
@@ -320,7 +321,7 @@ unsigned char *choose_kernel_location(unsigned char *input,
(unsigned long)output, output_size);
/* Walk e820 and find a random address. */
- random = find_random_addr(choice, output_size);
+ random = find_random_addr(choice, output_size + reserved_size);
if (!random) {
debug_putstr("KASLR could not find suitable E820 region...\n");
goto out;
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index cbed1407a5cd..06c18f6d1f13 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -207,6 +207,7 @@ relocated:
* Do the decompression, and jump to the new kernel..
*/
/* push arguments for decompress_kernel: */
+ pushl $reserved_size
pushl $z_output_len /* decompressed length */
leal z_extract_offset_negative(%ebx), %ebp
pushl %ebp /* output address */
@@ -217,7 +218,7 @@ relocated:
pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call decompress_kernel /* returns kernel location in %eax */
- addl $24, %esp
+ addl $28, %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 2884e0c3e8a5..02c518f8aca5 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -402,6 +402,8 @@ relocated:
* Do the decompression, and jump to the new kernel..
*/
pushq %rsi /* Save the real mode argument */
+ movq $reserved_size, %r9
+ pushq %r9
movq %rsi, %rdi /* real mode address */
leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
leaq input_data(%rip), %rdx /* input_data */
@@ -409,6 +411,7 @@ relocated:
movq %rbp, %r8 /* output target address */
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 57ab74df7eea..173062d32898 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -358,7 +358,8 @@ 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 output_len,
+ unsigned long reserved_size)
{
real_mode = rmode;
@@ -382,7 +383,8 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
free_mem_end_ptr = heap + BOOT_HEAP_SIZE;
output = choose_kernel_location(input_data, input_len,
- output, output_len);
+ output, output_len,
+ reserved_size);
/* Validate memory location choices. */
if ((unsigned long)output & (MIN_KERNEL_ALIGN - 1))
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 24e3e569a13c..fae4cef40f1f 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -59,7 +59,8 @@ int cmdline_find_option_bool(const char *option);
unsigned char *choose_kernel_location(unsigned char *input,
unsigned long input_size,
unsigned char *output,
- unsigned long output_size);
+ unsigned long output_size,
+ unsigned long reserved_size);
/* cpuflags.c */
bool has_cpuflag(int flag);
#else
@@ -67,7 +68,8 @@ static inline
unsigned char *choose_kernel_location(unsigned char *input,
unsigned long input_size,
unsigned char *output,
- unsigned long output_size)
+ unsigned long output_size,
+ unsigned long reserved_size)
{
return output;
}
diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c
index b669ab65bf6c..a31983ced81b 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -36,11 +36,12 @@ int main(int argc, char *argv[])
uint32_t olen;
long ilen;
unsigned long offs;
+ unsigned long reserved_size;
FILE *f = NULL;
int retval = 1;
- if (argc < 2) {
- fprintf(stderr, "Usage: %s compressed_file\n", argv[0]);
+ if (argc < 3) {
+ fprintf(stderr, "Usage: %s compressed_file reserved_size\n", argv[0]);
goto bail;
}
@@ -74,6 +75,7 @@ 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 */
+ reserved_size = atoi(argv[2]);
printf(".section \".rodata..compressed\",\"a\",@progbits\n");
printf(".globl z_input_len\n");
@@ -85,6 +87,8 @@ 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 reserved_size\n");
+ printf("reserved_size = 0x%lx\n", reserved_size);
printf(".globl input_data, input_data_end\n");
printf("input_data:\n");
diff --git a/arch/x86/tools/calc_reserved.awk b/arch/x86/tools/calc_reserved.awk
new file mode 100644
index 000000000000..2ca69682338a
--- /dev/null
+++ b/arch/x86/tools/calc_reserved.awk
@@ -0,0 +1,21 @@
+#!/bin/awk -f
+#
+# Calculate the amount of space that we have to reserve for .bss and .brk
+# sections
+#
+# Usage:
+# objdump -h a.out | awk -f calc_reserved.awk
+
+BEGIN {
+ sections = "^.bss$|^.brk$"
+ size = 0;
+}
+
+/^ *[0-9]+ [a-z._]+ *[0-9a-f]+/ {
+ if (match($2, sections))
+ size += strtonum("0x" $3);
+}
+
+END {
+ printf("%d\n", size);
+}
--
1.9.3
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