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. Here is an example of the overlap from a
x86_64 kernel in qemu (the ranges of physical addresses are presented):
Physical Address
0x0fe00000 --+--------------------+ <-- randomized base
/ | relocated kernel |
vmlinux.bin | (from vmlinux.bin) |
0x1336d000 (an ELF file) +--------------------+--
\ | | \
0x1376d870 --+--------------------+ |
| relocs table | |
0x13c1c2a8 +--------------------+ .bss and .brk
| | |
0x13ce6000 +--------------------+ |
| | /
0x13f77000 | initrd |--
| |
0x13fef374 +--------------------+
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 <[email protected]>
Signed-off-by: Junjie Mao <[email protected]>
[kees: switched to perl to avoid hex translation pain in mawk vs gawk]
[kees: calculated overlap without relocs table]
Signed-off-by: Kees Cook <[email protected]>
Cc: [email protected]
---
This version updates the commit log only.
Kees, please help review the documentation. Thanks!
Best Regards
Junjie Mao
---
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 | 13 ++++++++++---
arch/x86/boot/compressed/mkpiggy.c | 9 +++++++--
arch/x86/tools/calc_run_size.pl | 30 ++++++++++++++++++++++++++++++
6 files changed, 57 insertions(+), 9 deletions(-)
create mode 100644 arch/x86/tools/calc_run_size.pl
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 0fcd9133790c..14fe7cba21d1 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -75,8 +75,10 @@ suffix-$(CONFIG_KERNEL_XZ) := xz
suffix-$(CONFIG_KERNEL_LZO) := lzo
suffix-$(CONFIG_KERNEL_LZ4) := lz4
+RUN_SIZE = $(shell objdump -h vmlinux | \
+ perl $(srctree)/arch/x86/tools/calc_run_size.pl)
quiet_cmd_mkpiggy = MKPIGGY $@
- cmd_mkpiggy = $(obj)/mkpiggy $< > $@ || ( rm -f $@ ; false )
+ cmd_mkpiggy = $(obj)/mkpiggy $< $(RUN_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/head_32.S b/arch/x86/boot/compressed/head_32.S
index cbed1407a5cd..1d7fbbcc196d 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -207,7 +207,8 @@ relocated:
* Do the decompression, and jump to the new kernel..
*/
/* push arguments for decompress_kernel: */
- pushl $z_output_len /* decompressed length */
+ 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
pushl %ebp /* output address */
pushl $z_input_len /* input_len */
@@ -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..6b1766c6c082 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -402,13 +402,16 @@ 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 */
+ movq $z_output_len, %r9 /* decompressed length, end of relocs */
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..30dd59a9f0b4 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 run_size)
{
real_mode = rmode;
@@ -381,8 +382,14 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
free_mem_ptr = heap; /* Heap */
free_mem_end_ptr = heap + BOOT_HEAP_SIZE;
- output = choose_kernel_location(input_data, input_len,
- output, output_len);
+ /*
+ * 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.
+ */
+ output = choose_kernel_location(input_data, input_len, output,
+ output_len > run_size ? output_len
+ : run_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 b669ab65bf6c..d8222f213182 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -36,11 +36,13 @@ 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 < 2) {
- fprintf(stderr, "Usage: %s compressed_file\n", argv[0]);
+ if (argc < 3) {
+ fprintf(stderr, "Usage: %s compressed_file run_size\n",
+ argv[0]);
goto bail;
}
@@ -74,6 +76,7 @@ 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 */
+ run_size = atoi(argv[2]);
printf(".section \".rodata..compressed\",\"a\",@progbits\n");
printf(".globl z_input_len\n");
@@ -85,6 +88,8 @@ 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 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.pl b/arch/x86/tools/calc_run_size.pl
new file mode 100644
index 000000000000..0b0b124d3ece
--- /dev/null
+++ b/arch/x86/tools/calc_run_size.pl
@@ -0,0 +1,30 @@
+#!/usr/bin/perl
+#
+# Calculate the amount of space needed to run the kernel, including room for
+# the .bss and .brk sections.
+#
+# Usage:
+# objdump -h a.out | perl calc_run_size.pl
+use strict;
+
+my $mem_size = 0;
+my $file_offset = 0;
+
+my $sections=" *[0-9]+ \.(?:bss|brk) +";
+while (<>) {
+ if (/^$sections([0-9a-f]+) +(?:[0-9a-f]+ +){2}([0-9a-f]+)/) {
+ my $size = hex($1);
+ my $offset = hex($2);
+ $mem_size += $size;
+ if ($file_offset == 0) {
+ $file_offset = $offset;
+ } elsif ($file_offset != $offset) {
+ die ".bss and .brk lack common file offset\n";
+ }
+ }
+}
+
+if ($file_offset == 0) {
+ die "Never found .bss or .brk file offset\n";
+}
+printf("%d\n", $mem_size + $file_offset);
--
1.9.3
On Fri, Oct 31, 2014 at 6:40 AM, Junjie Mao <[email protected]> wrote:
> 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. Here is an example of the overlap from a
> x86_64 kernel in qemu (the ranges of physical addresses are presented):
>
> Physical Address
>
> 0x0fe00000 --+--------------------+ <-- randomized base
> / | relocated kernel |
> vmlinux.bin | (from vmlinux.bin) |
> 0x1336d000 (an ELF file) +--------------------+--
> \ | | \
> 0x1376d870 --+--------------------+ |
> | relocs table | |
> 0x13c1c2a8 +--------------------+ .bss and .brk
> | | |
> 0x13ce6000 +--------------------+ |
> | | /
> 0x13f77000 | initrd |--
> | |
> 0x13fef374 +--------------------+
>
> 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 <[email protected]>
> Signed-off-by: Junjie Mao <[email protected]>
> [kees: switched to perl to avoid hex translation pain in mawk vs gawk]
> [kees: calculated overlap without relocs table]
> Signed-off-by: Kees Cook <[email protected]>
> Cc: [email protected]
> ---
> This version updates the commit log only.
>
> Kees, please help review the documentation. Thanks!
Looks great, thanks! Can someone from x86 pull this please?
-Kees
>
> Best Regards
> Junjie Mao
> ---
> 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 | 13 ++++++++++---
> arch/x86/boot/compressed/mkpiggy.c | 9 +++++++--
> arch/x86/tools/calc_run_size.pl | 30 ++++++++++++++++++++++++++++++
> 6 files changed, 57 insertions(+), 9 deletions(-)
> create mode 100644 arch/x86/tools/calc_run_size.pl
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 0fcd9133790c..14fe7cba21d1 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -75,8 +75,10 @@ suffix-$(CONFIG_KERNEL_XZ) := xz
> suffix-$(CONFIG_KERNEL_LZO) := lzo
> suffix-$(CONFIG_KERNEL_LZ4) := lz4
>
> +RUN_SIZE = $(shell objdump -h vmlinux | \
> + perl $(srctree)/arch/x86/tools/calc_run_size.pl)
> quiet_cmd_mkpiggy = MKPIGGY $@
> - cmd_mkpiggy = $(obj)/mkpiggy $< > $@ || ( rm -f $@ ; false )
> + cmd_mkpiggy = $(obj)/mkpiggy $< $(RUN_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/head_32.S b/arch/x86/boot/compressed/head_32.S
> index cbed1407a5cd..1d7fbbcc196d 100644
> --- a/arch/x86/boot/compressed/head_32.S
> +++ b/arch/x86/boot/compressed/head_32.S
> @@ -207,7 +207,8 @@ relocated:
> * Do the decompression, and jump to the new kernel..
> */
> /* push arguments for decompress_kernel: */
> - pushl $z_output_len /* decompressed length */
> + 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
> pushl %ebp /* output address */
> pushl $z_input_len /* input_len */
> @@ -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..6b1766c6c082 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -402,13 +402,16 @@ 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 */
> + movq $z_output_len, %r9 /* decompressed length, end of relocs */
> 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..30dd59a9f0b4 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 run_size)
> {
> real_mode = rmode;
>
> @@ -381,8 +382,14 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
> free_mem_ptr = heap; /* Heap */
> free_mem_end_ptr = heap + BOOT_HEAP_SIZE;
>
> - output = choose_kernel_location(input_data, input_len,
> - output, output_len);
> + /*
> + * 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.
> + */
> + output = choose_kernel_location(input_data, input_len, output,
> + output_len > run_size ? output_len
> + : run_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 b669ab65bf6c..d8222f213182 100644
> --- a/arch/x86/boot/compressed/mkpiggy.c
> +++ b/arch/x86/boot/compressed/mkpiggy.c
> @@ -36,11 +36,13 @@ 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 < 2) {
> - fprintf(stderr, "Usage: %s compressed_file\n", argv[0]);
> + if (argc < 3) {
> + fprintf(stderr, "Usage: %s compressed_file run_size\n",
> + argv[0]);
> goto bail;
> }
>
> @@ -74,6 +76,7 @@ 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 */
> + run_size = atoi(argv[2]);
>
> printf(".section \".rodata..compressed\",\"a\",@progbits\n");
> printf(".globl z_input_len\n");
> @@ -85,6 +88,8 @@ 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 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.pl b/arch/x86/tools/calc_run_size.pl
> new file mode 100644
> index 000000000000..0b0b124d3ece
> --- /dev/null
> +++ b/arch/x86/tools/calc_run_size.pl
> @@ -0,0 +1,30 @@
> +#!/usr/bin/perl
> +#
> +# Calculate the amount of space needed to run the kernel, including room for
> +# the .bss and .brk sections.
> +#
> +# Usage:
> +# objdump -h a.out | perl calc_run_size.pl
> +use strict;
> +
> +my $mem_size = 0;
> +my $file_offset = 0;
> +
> +my $sections=" *[0-9]+ \.(?:bss|brk) +";
> +while (<>) {
> + if (/^$sections([0-9a-f]+) +(?:[0-9a-f]+ +){2}([0-9a-f]+)/) {
> + my $size = hex($1);
> + my $offset = hex($2);
> + $mem_size += $size;
> + if ($file_offset == 0) {
> + $file_offset = $offset;
> + } elsif ($file_offset != $offset) {
> + die ".bss and .brk lack common file offset\n";
> + }
> + }
> +}
> +
> +if ($file_offset == 0) {
> + die "Never found .bss or .brk file offset\n";
> +}
> +printf("%d\n", $mem_size + $file_offset);
> --
> 1.9.3
--
Kees Cook
Chrome OS Security
Commit-ID: e6023367d779060fddc9a52d1f474085b2b36298
Gitweb: http://git.kernel.org/tip/e6023367d779060fddc9a52d1f474085b2b36298
Author: Junjie Mao <[email protected]>
AuthorDate: Fri, 31 Oct 2014 21:40:38 +0800
Committer: Thomas Gleixner <[email protected]>
CommitDate: Sat, 1 Nov 2014 22:20:50 +0100
x86, kaslr: Prevent .bss from overlaping initrd
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. Here is an example of the overlap from a
x86_64 kernel in qemu (the ranges of physical addresses are presented):
Physical Address
0x0fe00000 --+--------------------+ <-- randomized base
/ | relocated kernel |
vmlinux.bin | (from vmlinux.bin) |
0x1336d000 (an ELF file) +--------------------+--
\ | | \
0x1376d870 --+--------------------+ |
| relocs table | |
0x13c1c2a8 +--------------------+ .bss and .brk
| | |
0x13ce6000 +--------------------+ |
| | /
0x13f77000 | initrd |--
| |
0x13fef374 +--------------------+
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.
[kees: switched to perl to avoid hex translation pain in mawk vs gawk]
[kees: calculated overlap without relocs table]
Fixes: 82fa9637a2 ("x86, kaslr: Select random position from e820 maps")
Reported-by: Fengguang Wu <[email protected]>
Signed-off-by: Junjie Mao <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Cc: Josh Triplett <[email protected]>
Cc: Matt Fleming <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>
---
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 | 13 ++++++++++---
arch/x86/boot/compressed/mkpiggy.c | 9 +++++++--
arch/x86/tools/calc_run_size.pl | 30 ++++++++++++++++++++++++++++++
6 files changed, 57 insertions(+), 9 deletions(-)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 704f58a..be1e07d 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -76,8 +76,10 @@ suffix-$(CONFIG_KERNEL_XZ) := xz
suffix-$(CONFIG_KERNEL_LZO) := lzo
suffix-$(CONFIG_KERNEL_LZ4) := lz4
+RUN_SIZE = $(shell objdump -h vmlinux | \
+ perl $(srctree)/arch/x86/tools/calc_run_size.pl)
quiet_cmd_mkpiggy = MKPIGGY $@
- cmd_mkpiggy = $(obj)/mkpiggy $< > $@ || ( rm -f $@ ; false )
+ cmd_mkpiggy = $(obj)/mkpiggy $< $(RUN_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/head_32.S b/arch/x86/boot/compressed/head_32.S
index cbed140..1d7fbbc 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -207,7 +207,8 @@ relocated:
* Do the decompression, and jump to the new kernel..
*/
/* push arguments for decompress_kernel: */
- pushl $z_output_len /* decompressed length */
+ 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
pushl %ebp /* output address */
pushl $z_input_len /* input_len */
@@ -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 2884e0c..6b1766c 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -402,13 +402,16 @@ 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 */
+ movq $z_output_len, %r9 /* decompressed length, end of relocs */
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 57ab74d..30dd59a 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 run_size)
{
real_mode = rmode;
@@ -381,8 +382,14 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
free_mem_ptr = heap; /* Heap */
free_mem_end_ptr = heap + BOOT_HEAP_SIZE;
- output = choose_kernel_location(input_data, input_len,
- output, output_len);
+ /*
+ * 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.
+ */
+ output = choose_kernel_location(input_data, input_len, output,
+ output_len > run_size ? output_len
+ : run_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 b669ab6..d8222f2 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -36,11 +36,13 @@ 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 < 2) {
- fprintf(stderr, "Usage: %s compressed_file\n", argv[0]);
+ if (argc < 3) {
+ fprintf(stderr, "Usage: %s compressed_file run_size\n",
+ argv[0]);
goto bail;
}
@@ -74,6 +76,7 @@ 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 */
+ run_size = atoi(argv[2]);
printf(".section \".rodata..compressed\",\"a\",@progbits\n");
printf(".globl z_input_len\n");
@@ -85,6 +88,8 @@ 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 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.pl b/arch/x86/tools/calc_run_size.pl
new file mode 100644
index 0000000..0b0b124
--- /dev/null
+++ b/arch/x86/tools/calc_run_size.pl
@@ -0,0 +1,30 @@
+#!/usr/bin/perl
+#
+# Calculate the amount of space needed to run the kernel, including room for
+# the .bss and .brk sections.
+#
+# Usage:
+# objdump -h a.out | perl calc_run_size.pl
+use strict;
+
+my $mem_size = 0;
+my $file_offset = 0;
+
+my $sections=" *[0-9]+ \.(?:bss|brk) +";
+while (<>) {
+ if (/^$sections([0-9a-f]+) +(?:[0-9a-f]+ +){2}([0-9a-f]+)/) {
+ my $size = hex($1);
+ my $offset = hex($2);
+ $mem_size += $size;
+ if ($file_offset == 0) {
+ $file_offset = $offset;
+ } elsif ($file_offset != $offset) {
+ die ".bss and .brk lack common file offset\n";
+ }
+ }
+}
+
+if ($file_offset == 0) {
+ die "Never found .bss or .brk file offset\n";
+}
+printf("%d\n", $mem_size + $file_offset);
On Fri, Oct 31 2014, Junjie Mao wrote:
> 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. Here is an example of the overlap from a
> x86_64 kernel in qemu (the ranges of physical addresses are presented):
>
> Physical Address
>
> 0x0fe00000 --+--------------------+ <-- randomized base
> / | relocated kernel |
> vmlinux.bin | (from vmlinux.bin) |
> 0x1336d000 (an ELF file) +--------------------+--
> \ | | \
> 0x1376d870 --+--------------------+ |
> | relocs table | |
> 0x13c1c2a8 +--------------------+ .bss and .brk
> | | |
> 0x13ce6000 +--------------------+ |
> | | /
> 0x13f77000 | initrd |--
> | |
> 0x13fef374 +--------------------+
>
> 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 <[email protected]>
> Signed-off-by: Junjie Mao <[email protected]>
> [kees: switched to perl to avoid hex translation pain in mawk vs gawk]
> [kees: calculated overlap without relocs table]
> Signed-off-by: Kees Cook <[email protected]>
> Cc: [email protected]
> ---
> This version updates the commit log only.
>
> Kees, please help review the documentation. Thanks!
>
> Best Regards
> Junjie Mao
[...]
> diff --git a/arch/x86/tools/calc_run_size.pl b/arch/x86/tools/calc_run_size.pl
> new file mode 100644
> index 000000000000..0b0b124d3ece
> --- /dev/null
> +++ b/arch/x86/tools/calc_run_size.pl
> @@ -0,0 +1,30 @@
> +#!/usr/bin/perl
> +#
> +# Calculate the amount of space needed to run the kernel, including room for
> +# the .bss and .brk sections.
> +#
> +# Usage:
> +# objdump -h a.out | perl calc_run_size.pl
> +use strict;
> +
> +my $mem_size = 0;
> +my $file_offset = 0;
> +
> +my $sections=" *[0-9]+ \.(?:bss|brk) +";
> +while (<>) {
> + if (/^$sections([0-9a-f]+) +(?:[0-9a-f]+ +){2}([0-9a-f]+)/) {
> + my $size = hex($1);
> + my $offset = hex($2);
> + $mem_size += $size;
> + if ($file_offset == 0) {
> + $file_offset = $offset;
> + } elsif ($file_offset != $offset) {
> + die ".bss and .brk lack common file offset\n";
> + }
> + }
> +}
> +
> +if ($file_offset == 0) {
> + die "Never found .bss or .brk file offset\n";
> +}
> +printf("%d\n", $mem_size + $file_offset);
Given that bss and brk are nobits (i.e. only ALLOC) sections, does
file_offset make sense as a load address. This fails with gold:
$ git checkout v3.18-rc5
$ make # with gold
[...]
..bss and .brk lack common file offset
..bss and .brk lack common file offset
..bss and .brk lack common file offset
..bss and .brk lack common file offset
MKPIGGY arch/x86/boot/compressed/piggy.S
Usage: arch/x86/boot/compressed/mkpiggy compressed_file run_size
make[2]: *** [arch/x86/boot/compressed/piggy.S] Error 1
make[1]: *** [arch/x86/boot/compressed/vmlinux] Error 2
make: *** [bzImage] Error 2
In ld.bfd brk/bss file_offsets match, but they differ with ld.gold:
$ objdump -h vmlinux.ld
[...]
0 .text 00818bb3 ffffffff81000000 0000000001000000 00200000 2**12
CONTENTS, ALLOC, LOAD, READONLY, CODE
[...]
26 .bss 000e0000 ffffffff81fe8000 0000000001fe8000 013e8000 2**12
ALLOC
27 .brk 00026000 ffffffff820c8000 00000000020c8000 013e8000 2**0
ALLOC
$ objdump -h vmlinux.ld | perl arch/x86/tools/calc_run_size.pl
21946368
# aka 0x14ee000
$ objdump -h vmlinux.gold
[...]
0 .text 00818bb3 ffffffff81000000 0000000001000000 00001000 2**12
CONTENTS, ALLOC, LOAD, READONLY, CODE
[...]
26 .bss 000e0000 ffffffff81feb000 0000000001feb000 00e90000 2**12
ALLOC
27 .brk 00026000 ffffffff820cb000 00000000020cb000 00f70000 2**0
ALLOC
On Mon, Nov 17 2014, Greg Thelen wrote:
[...]
> Given that bss and brk are nobits (i.e. only ALLOC) sections, does
> file_offset make sense as a load address. This fails with gold:
>
> $ git checkout v3.18-rc5
> $ make # with gold
> [...]
> ..bss and .brk lack common file offset
> ..bss and .brk lack common file offset
> ..bss and .brk lack common file offset
> ..bss and .brk lack common file offset
> MKPIGGY arch/x86/boot/compressed/piggy.S
> Usage: arch/x86/boot/compressed/mkpiggy compressed_file run_size
> make[2]: *** [arch/x86/boot/compressed/piggy.S] Error 1
> make[1]: *** [arch/x86/boot/compressed/vmlinux] Error 2
> make: *** [bzImage] Error 2
[...]
I just saw http://www.spinics.net/lists/kernel/msg1869328.html which
fixes things for me. Sorry for the noise.
On 11/17/2014 06:23 PM, Greg Thelen wrote:
>
> On Mon, Nov 17 2014, Greg Thelen wrote:
> [...]
>> Given that bss and brk are nobits (i.e. only ALLOC) sections, does
>> file_offset make sense as a load address. This fails with gold:
>>
It really doesn't. We have that information elsewhere.
-hpa