[PATCH V4 Resend] ZBOOT: fix stack protector in compressed boot phase

[PATCH V4 Resend] ZBOOT: fix stack protector in compressed boot phase

[Huacai Chen]

Call __stack_chk_guard_setup() in decompress_kernel() is too late that
stack checking always fails for decompress_kernel() itself. So remove
__stack_chk_guard_setup() and initialize __stack_chk_guard before we
call decompress_kernel().

Original code comes from ARM but also used for MIPS and SH, so fix them
together. If without this fix, compressed booting of these archs will
fail because stack checking is enabled by default (>=4.16).

V1 -> V2: Fix build on ARM.
V2 -> V3: Fix build on SuperH.
V3 -> V4: Initialize __stack_chk_guard in C code as a constant.

Cc: stable@vger.kernel.org
Signed-off-by: Huacai Chen <chenhc@lemote.com>
---
 arch/arm/boot/compressed/misc.c        | 9 +--------
 arch/mips/boot/compressed/decompress.c | 9 +--------
 arch/sh/boot/compressed/misc.c         | 9 +--------
 3 files changed, 3 insertions(+), 24 deletions(-)

diff --git a/arch/arm/boot/compressed/misc.c b/arch/arm/boot/compressed/misc.c
index 16a8a80..e8fe51f 100644
--- a/arch/arm/boot/compressed/misc.c
+++ b/arch/arm/boot/compressed/misc.c
@@ -128,12 +128,7 @@ asmlinkage void __div0(void)
 	error("Attempting division by 0!");
 }
 
-unsigned long __stack_chk_guard;
-
-void __stack_chk_guard_setup(void)
-{
-	__stack_chk_guard = 0x000a0dff;
-}
+const unsigned long __stack_chk_guard = 0x000a0dff;
 
 void __stack_chk_fail(void)
 {
@@ -150,8 +145,6 @@ decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p,
 {
 	int ret;
 
-	__stack_chk_guard_setup();
-
 	output_data		= (unsigned char *)output_start;
 	free_mem_ptr		= free_mem_ptr_p;
 	free_mem_end_ptr	= free_mem_ptr_end_p;
diff --git a/arch/mips/boot/compressed/decompress.c b/arch/mips/boot/compressed/decompress.c
index fdf99e9..81df904 100644
--- a/arch/mips/boot/compressed/decompress.c
+++ b/arch/mips/boot/compressed/decompress.c
@@ -76,12 +76,7 @@ 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;
-}
+const unsigned long __stack_chk_guard = 0x000a0dff;
 
 void __stack_chk_fail(void)
 {
@@ -92,8 +87,6 @@ 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);
diff --git a/arch/sh/boot/compressed/misc.c b/arch/sh/boot/compressed/misc.c
index 627ce8e..c15cac9 100644
--- a/arch/sh/boot/compressed/misc.c
+++ b/arch/sh/boot/compressed/misc.c
@@ -104,12 +104,7 @@ static void error(char *x)
 	while(1);	/* Halt */
 }
 
-unsigned long __stack_chk_guard;
-
-void __stack_chk_guard_setup(void)
-{
-	__stack_chk_guard = 0x000a0dff;
-}
+const unsigned long __stack_chk_guard = 0x000a0dff;
 
 void __stack_chk_fail(void)
 {
@@ -130,8 +125,6 @@ void decompress_kernel(void)
 {
 	unsigned long output_addr;
 
-	__stack_chk_guard_setup();
-
 #ifdef CONFIG_SUPERH64
 	output_addr = (CONFIG_MEMORY_START + 0x2000);
 #else
-- 
2.7.0

Re: [PATCH V4 Resend] ZBOOT: fix stack protector in compressed boot phase

[James Hogan]

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On Wed, Mar 28, 2018 at 04:48:53PM +0800, Huacai Chen wrote:
> diff --git a/arch/mips/boot/compressed/decompress.c b/arch/mips/boot/compressed/decompress.c
> index fdf99e9..81df904 100644
> --- a/arch/mips/boot/compressed/decompress.c
> +++ b/arch/mips/boot/compressed/decompress.c
> @@ -76,12 +76,7 @@ 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;
> -}
> +const unsigned long __stack_chk_guard = 0x000a0dff;
>  
>  void __stack_chk_fail(void)
>  {
> @@ -92,8 +87,6 @@ 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);

This looks good to me, though I've Cc'd Kees as apparently the original
author from commit 8779657d29c0 ("stackprotector: Introduce
CONFIG_CC_STACKPROTECTOR_STRONG") in case there was a particular reason
this wasn't done in the first place.

Acked-by: James Hogan <jhogan@kernel.org>

(Happy to apply with acks from Kees and ARM, SH maintainers if nobody
else does).

Cheers
James

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Re: [PATCH V4 Resend] ZBOOT: fix stack protector in compressed boot phase

[Kees Cook]

On Wed, Mar 28, 2018 at 8:21 AM, James Hogan <jhogan@kernel.org> wrote:
> On Wed, Mar 28, 2018 at 04:48:53PM +0800, Huacai Chen wrote:
>> diff --git a/arch/mips/boot/compressed/decompress.c b/arch/mips/boot/compressed/decompress.c
>> index fdf99e9..81df904 100644
>> --- a/arch/mips/boot/compressed/decompress.c
>> +++ b/arch/mips/boot/compressed/decompress.c
>> @@ -76,12 +76,7 @@ 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;
>> -}
>> +const unsigned long __stack_chk_guard = 0x000a0dff;
>>
>>  void __stack_chk_fail(void)
>>  {
>> @@ -92,8 +87,6 @@ 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);
>
> This looks good to me, though I've Cc'd Kees as apparently the original
> author from commit 8779657d29c0 ("stackprotector: Introduce

I wonder what changed in the compiler -- I regularly boot
stack-protected ARM images. Regardless, this is fine. :)

> CONFIG_CC_STACKPROTECTOR_STRONG") in case there was a particular reason
> this wasn't done in the first place.

I think I was copying from other places? It's been long enough that I
don't remember, actually. :)

> Acked-by: James Hogan <jhogan@kernel.org>

Acked-by: Kees Cook <keescook@chromium.org>

> (Happy to apply with acks from Kees and ARM, SH maintainers if nobody
> else does).

That'd be fine by me, FWIW. Thanks!

-Kees

-- 
Kees Cook
Pixel Security

Re: [PATCH V4 Resend] ZBOOT: fix stack protector in compressed boot phase

[Rich Felker]

On Wed, Mar 28, 2018 at 04:48:53PM +0800, Huacai Chen wrote:
> Call __stack_chk_guard_setup() in decompress_kernel() is too late that
> stack checking always fails for decompress_kernel() itself. So remove
> __stack_chk_guard_setup() and initialize __stack_chk_guard before we
> call decompress_kernel().
> 
> Original code comes from ARM but also used for MIPS and SH, so fix them
> together. If without this fix, compressed booting of these archs will
> fail because stack checking is enabled by default (>=4.16).
> 
> V1 -> V2: Fix build on ARM.
> V2 -> V3: Fix build on SuperH.
> V3 -> V4: Initialize __stack_chk_guard in C code as a constant.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> ---
>  arch/arm/boot/compressed/misc.c        | 9 +--------
>  arch/mips/boot/compressed/decompress.c | 9 +--------
>  arch/sh/boot/compressed/misc.c         | 9 +--------
>  3 files changed, 3 insertions(+), 24 deletions(-)
> 
> [...]
> 
> diff --git a/arch/sh/boot/compressed/misc.c b/arch/sh/boot/compressed/misc.c
> index 627ce8e..c15cac9 100644
> --- a/arch/sh/boot/compressed/misc.c
> +++ b/arch/sh/boot/compressed/misc.c
> @@ -104,12 +104,7 @@ static void error(char *x)
>  	while(1);	/* Halt */
>  }
>  
> -unsigned long __stack_chk_guard;
> -
> -void __stack_chk_guard_setup(void)
> -{
> -	__stack_chk_guard = 0x000a0dff;
> -}
> +const unsigned long __stack_chk_guard = 0x000a0dff;
>  
>  void __stack_chk_fail(void)
>  {
> @@ -130,8 +125,6 @@ void decompress_kernel(void)
>  {
>  	unsigned long output_addr;
>  
> -	__stack_chk_guard_setup();
> -
>  #ifdef CONFIG_SUPERH64
>  	output_addr = (CONFIG_MEMORY_START + 0x2000);
>  #else
> -- 
> 2.7.0

LGTM.

Acked-by: Rich Felker <dalias@libc.org>

Rich