linux-kernel - Re: [PATCH v3 11/12] lkdtm: Fix execute_[user]

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Date:   Fri, 17 Dec 2021 11:49:28 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Kees Cook <keescook@...omium.org>,
        Michael Ellerman <mpe@...erman.id.au>
CC:     Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Paul Mackerras <paulus@...ba.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v3 11/12] lkdtm: Fix execute_[user]_location()

Hi Kees,

Le 17/10/2021 à 14:38, Christophe Leroy a écrit :
> execute_location() and execute_user_location() intent
> to copy do_nothing() text and execute it at a new location.
> However, at the time being it doesn't copy do_nothing() function
> but do_nothing() function descriptor which still points to the
> original text. So at the end it still executes do_nothing() at
> its original location allthough using a copied function descriptor.
> 
> So, fix that by really copying do_nothing() text and build a new
> function descriptor by copying do_nothing() function descriptor and
> updating the target address with the new location.
> 
> Also fix the displayed addresses by dereferencing do_nothing()
> function descriptor.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>

Do you have any comment to this patch and to patch 12 ?

If not, is it ok to get your acked-by ?

Thanks
Christophe

> ---
>   drivers/misc/lkdtm/perms.c | 37 ++++++++++++++++++++++++++++---------
>   1 file changed, 28 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
> index 035fcca441f0..1cf24c4a79e9 100644
> --- a/drivers/misc/lkdtm/perms.c
> +++ b/drivers/misc/lkdtm/perms.c
> @@ -44,19 +44,34 @@ static noinline void do_overwritten(void)
>   	return;
>   }
>   
> +static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)
> +{
> +	if (!have_function_descriptors())
> +		return dst;
> +
> +	memcpy(fdesc, do_nothing, sizeof(*fdesc));
> +	fdesc->addr = (unsigned long)dst;
> +	barrier();
> +
> +	return fdesc;
> +}
> +
>   static noinline void execute_location(void *dst, bool write)
>   {
> -	void (*func)(void) = dst;
> +	void (*func)(void);
> +	func_desc_t fdesc;
> +	void *do_nothing_text = dereference_function_descriptor(do_nothing);
>   
> -	pr_info("attempting ok execution at %px\n", do_nothing);
> +	pr_info("attempting ok execution at %px\n", do_nothing_text);
>   	do_nothing();
>   
>   	if (write == CODE_WRITE) {
> -		memcpy(dst, do_nothing, EXEC_SIZE);
> +		memcpy(dst, do_nothing_text, EXEC_SIZE);
>   		flush_icache_range((unsigned long)dst,
>   				   (unsigned long)dst + EXEC_SIZE);
>   	}
> -	pr_info("attempting bad execution at %px\n", func);
> +	pr_info("attempting bad execution at %px\n", dst);
> +	func = setup_function_descriptor(&fdesc, dst);
>   	func();
>   	pr_err("FAIL: func returned\n");
>   }
> @@ -66,16 +81,19 @@ static void execute_user_location(void *dst)
>   	int copied;
>   
>   	/* Intentionally crossing kernel/user memory boundary. */
> -	void (*func)(void) = dst;
> +	void (*func)(void);
> +	func_desc_t fdesc;
> +	void *do_nothing_text = dereference_function_descriptor(do_nothing);
>   
> -	pr_info("attempting ok execution at %px\n", do_nothing);
> +	pr_info("attempting ok execution at %px\n", do_nothing_text);
>   	do_nothing();
>   
> -	copied = access_process_vm(current, (unsigned long)dst, do_nothing,
> +	copied = access_process_vm(current, (unsigned long)dst, do_nothing_text,
>   				   EXEC_SIZE, FOLL_WRITE);
>   	if (copied < EXEC_SIZE)
>   		return;
> -	pr_info("attempting bad execution at %px\n", func);
> +	pr_info("attempting bad execution at %px\n", dst);
> +	func = setup_function_descriptor(&fdesc, dst);
>   	func();
>   	pr_err("FAIL: func returned\n");
>   }
> @@ -153,7 +171,8 @@ void lkdtm_EXEC_VMALLOC(void)
>   
>   void lkdtm_EXEC_RODATA(void)
>   {
> -	execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
> +	execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing),
> +			 CODE_AS_IS);
>   }
>   
>   void lkdtm_EXEC_USERSPACE(void)
>