2014-06-24 23:00:21

by Ben Chan

Subject: [PATCH] MIPS: ZBOOT: implement stack protector in compressed boot phase

This patch implements the stack protector code in MIPS compressed boot
phase based on the same code added to arm in commit
8779657d29c0ebcc0c94ede4df2f497baf1b563f "stackprotector: Introduce
CONFIG_CC_STACKPROTECTOR_STRONG" by Kees Cook <[email protected]>

Signed-off-by: Ben Chan <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Olof Johansson <[email protected]>
---
arch/mips/boot/compressed/decompress.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/arch/mips/boot/compressed/decompress.c b/arch/mips/boot/compressed/decompress.c
index c00c4dd..b49c7ad 100644
--- a/arch/mips/boot/compressed/decompress.c
+++ b/arch/mips/boot/compressed/decompress.c
@@ -67,10 +67,24 @@ void error(char *x)
#include "../../../../lib/decompress_unxz.c"
#endif

+unsigned long __stack_chk_guard;
+
+void __stack_chk_guard_setup(void)
+{
+ __stack_chk_guard = 0x000a0dff;
+}
+
+void __stack_chk_fail(void)
+{
+ error("stack-protector: Kernel stack is corrupted\n");
+}
+
void decompress_kernel(unsigned long boot_heap_start)
{
unsigned long zimage_start, zimage_size;

+ __stack_chk_guard_setup();
+
zimage_start = (unsigned long)(&__image_begin);
zimage_size = (unsigned long)(&__image_end) -
(unsigned long)(&__image_begin);
--
2.0.0.526.g5318336

2014-06-24 23:55:04

by Kees Cook

Subject: Re: [PATCH] MIPS: ZBOOT: implement stack protector in compressed boot phase

On Tue, Jun 24, 2014 at 4:00 PM, Ben Chan <[email protected]> wrote:
> This patch implements the stack protector code in MIPS compressed boot
> phase based on the same code added to arm in commit
> 8779657d29c0ebcc0c94ede4df2f497baf1b563f "stackprotector: Introduce
> CONFIG_CC_STACKPROTECTOR_STRONG" by Kees Cook <[email protected]>
>
> Signed-off-by: Ben Chan <[email protected]>
> Cc: Kees Cook <[email protected]>
> Cc: Olof Johansson <[email protected]>
> ---
> arch/mips/boot/compressed/decompress.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/arch/mips/boot/compressed/decompress.c b/arch/mips/boot/compressed/decompress.c
> index c00c4dd..b49c7ad 100644
> --- a/arch/mips/boot/compressed/decompress.c
> +++ b/arch/mips/boot/compressed/decompress.c
> @@ -67,10 +67,24 @@ void error(char *x)
> #include "../../../../lib/decompress_unxz.c"
> #endif
>
> +unsigned long __stack_chk_guard;
> +
> +void __stack_chk_guard_setup(void)
> +{
> + __stack_chk_guard = 0x000a0dff;
> +}
> +
> +void __stack_chk_fail(void)
> +{
> + error("stack-protector: Kernel stack is corrupted\n");
> +}
> +
> void decompress_kernel(unsigned long boot_heap_start)
> {
> unsigned long zimage_start, zimage_size;
>
> + __stack_chk_guard_setup();
> +
> zimage_start = (unsigned long)(&__image_begin);
> zimage_size = (unsigned long)(&__image_end) -
> (unsigned long)(&__image_begin);
> --
> 2.0.0.526.g5318336

Yup, that looks correct to me. As in the ARM case, gathering entropy
for the canary here is overkill, so this is sufficient to build and
provide basic canary support in the decompression phase of boot.

Reviewed-by: Kees Cook <[email protected]>

Thanks!

-Kees

--
Kees Cook
Chrome OS Security