[PATCH] powerpc/kasan: Force thread size increase with KASAN

[Christophe Leroy]

Le 01/06/2022 à 16:31, Michael Ellerman a écrit :
> KASAN causes increased stack usage, which can lead to stack overflows.
> 
> The logic in Kconfig to suggest a larger default doesn't work if a user
> has CONFIG_EXPERT enabled and has an existing .config with a smaller
> value.
> 
> Follow the lead of x86 and arm64, and force the thread size to be
> increased when KASAN is enabled.
> 
> That also has the effect of enlarging the stack for 64-bit KASAN builds,
> which is also desirable.
> 
> Fixes: edbadaf06710 ("powerpc/kasan: Fix stack overflow by increasing THREAD_SHIFT")
> Reported-by: Erhard Furtner <erhard_f at mailbox.org>
> Reported-by: Christophe Leroy <christophe.leroy at csgroup.eu>
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> ---
>   arch/powerpc/Kconfig                   | 1 -
>   arch/powerpc/include/asm/thread_info.h | 9 +++++++--
>   2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 54dbbb1d4b36..b1760d615bb7 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -790,7 +790,6 @@ config THREAD_SHIFT
>   	range 13 15
>   	default "15" if PPC_256K_PAGES
>   	default "14" if PPC64
> -	default "14" if KASAN
>   	default "13"
>   	help
>   	  Used to define the stack size. The default is almost always what you
> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> index 125328d1b980..c9735f93f8e6 100644
> --- a/arch/powerpc/include/asm/thread_info.h
> +++ b/arch/powerpc/include/asm/thread_info.h
> @@ -14,12 +14,17 @@
>   
>   #ifdef __KERNEL__
>   
> -#if defined(CONFIG_VMAP_STACK) && CONFIG_THREAD_SHIFT < PAGE_SHIFT
> -#define THREAD_SHIFT		PAGE_SHIFT
> +#ifdef CONFIG_KASAN
> +#define THREAD_SHIFT		(CONFIG_THREAD_SHIFT + 1)
>   #else
>   #define THREAD_SHIFT		CONFIG_THREAD_SHIFT
>   #endif
>   
> +#if defined(CONFIG_VMAP_STACK) && THREAD_SHIFT < PAGE_SHIFT
> +#undef THREAD_SHIFT

I dislike this undef.

I would was done

#ifdef CONFIG_KASAN
#define MIN_THREAD_SHIFT	(CONFIG_THREAD_SHIFT + 1)
#else
#define MIN_THREAD_SHIFT	CONFIG_THREAD_SHIFT
#endif

#if defined(CONFIG_VMAP_STACK) && MIN_THREAD_SHIFT < PAGE_SHIFT
#define THREAD_SHIFT		PAGE_SHIFT
#else
#define THREAD_SHIFT		MIN_THREAD_SHIFT
#endif


> +#define THREAD_SHIFT		PAGE_SHIFT
> +#endif
> +
>   #define THREAD_SIZE		(1 << THREAD_SHIFT)
>   
>   /*