linux-kernel - Re: [PATCH v3 1/3] lkdtm: Check for SMEP clearing protections

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Date:   Tue, 18 Jun 2019 09:10:13 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Kees Cook <keescook@...omium.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v3 1/3] lkdtm: Check for SMEP clearing protections

On 18/06/2019 06.55, Kees Cook wrote:

> +#else
> +	pr_err("FAIL: this test is x86_64-only\n");
> +#endif
> +}

Why expose it at all on all other architectures? If you wrap the
CRASHTYPE() in an #ifdef, you can also guard the whole lkdtm_UNSET_SMEP
definition (the declaration in lkdtm.h can stay, possibly with a comment
saying /* x86-64 only */).

> diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
> index b51cf182b031..58cfd713f8dc 100644
> --- a/drivers/misc/lkdtm/core.c
> +++ b/drivers/misc/lkdtm/core.c
> @@ -123,6 +123,7 @@ static const struct crashtype crashtypes[] = {
>  	CRASHTYPE(CORRUPT_LIST_ADD),
>  	CRASHTYPE(CORRUPT_LIST_DEL),
>  	CRASHTYPE(CORRUPT_USER_DS),
> +	CRASHTYPE(UNSET_SMEP),
>  	CRASHTYPE(CORRUPT_STACK),
>  	CRASHTYPE(CORRUPT_STACK_STRONG),
>  	CRASHTYPE(STACK_GUARD_PAGE_LEADING),
> diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
> index b69ee004a3f7..d7eb5a8f1da4 100644
> --- a/drivers/misc/lkdtm/lkdtm.h
> +++ b/drivers/misc/lkdtm/lkdtm.h
> @@ -26,6 +26,7 @@ void lkdtm_CORRUPT_LIST_DEL(void);
>  void lkdtm_CORRUPT_USER_DS(void);
>  void lkdtm_STACK_GUARD_PAGE_LEADING(void);
>  void lkdtm_STACK_GUARD_PAGE_TRAILING(void);
> +void lkdtm_UNSET_SMEP(void);
>  
>  /* lkdtm_heap.c */
>  void lkdtm_OVERWRITE_ALLOCATION(void);
Rasmus