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

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Date:   Fri, 17 Dec 2021 18:12:19 +0100
From:   Helge Deller <deller@....de>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Kees Cook <keescook@...omium.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     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()

On 12/17/21 12:49, Christophe Leroy wrote:
> 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 ?


Hi Christophe,

I think this whole series is a nice cleanup and harmonization
of how function descriptors are used.

At least for the PA-RISC parts you may add:
Acked-by: Helge Deller <deller@....de>

Thanks!
Helge

>
>> ---
>>   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)