Re: [PATCH] arm64: Make TSK_STACK_CANARY more accurate defined

[Will Deacon]

On Mon, Jul 13, 2020 at 04:03:33AM +0000, guoren@xxxxxxxxxx wrote:
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> 
> TSK_STACK_CANARY only used in arm64/Makefile with
> CONFIG_STACKPROTECTOR_PER_TASK wrap. So use the same policy in
> asm-offset.c.
> 
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Co-developed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/asm-offsets.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 0577e21..37d5d3d 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -39,7 +39,7 @@ int main(void)
>    DEFINE(TSK_TI_SCS_SP,		offsetof(struct task_struct, thread_info.scs_sp));
>  #endif
>    DEFINE(TSK_STACK,		offsetof(struct task_struct, stack));
> -#ifdef CONFIG_STACKPROTECTOR
> +#ifdef CONFIG_STACKPROTECTOR_PER_TASK
>    DEFINE(TSK_STACK_CANARY,	offsetof(struct task_struct, stack_canary));
>  #endif

I don't think this really makese much sense. The 'stack_canary' field in
'struct task_struct' is defined as:

#ifdef CONFIG_STACKPROTECTOR
        /* Canary value for the -fstack-protector GCC feature: */
        unsigned long                   stack_canary;
#endif

so I think it makes sense to follow that in asm-offsets.c

Does the current code actually cause a problem?

Will