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

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Message-ID: <c635dff6-2bca-3486-014f-12ae00bd1777@csgroup.eu>
Date:   Wed, 19 Jan 2022 20:28:54 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Kees Cook <keescook@...omium.org>
Cc:     Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-ia64@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Paul Mackerras <paulus@...ba.org>,
        Arnd Bergmann <arnd@...db.de>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v3 11/12] lkdtm: Fix execute_[user]_location()

Hi Kees,


Le 17/12/2021 à 12:49, Christophe Leroy a écrit :
> 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 ?

Any feedback please, even if it's to say no feedback ?

Many thanks,
Christophe

> 
> 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)
>>