From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Kees Cook <keescook@chromium.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Andrew Morton <akpm@linux-foundation.org>,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
Helge Deller <deller@gmx.de>, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org,
linux-arch@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v1 09/10] lkdtm: Fix lkdtm_EXEC_RODATA()
Date: Wed, 13 Oct 2021 14:45:11 +0200 [thread overview]
Message-ID: <c87e4e91-ee66-77b8-863a-27a34f41623e@csgroup.eu> (raw)
In-Reply-To: <134b968f-f65f-cd74-3db1-fff60e5ebeb8@csgroup.eu>
Le 13/10/2021 à 09:48, Christophe Leroy a écrit :
>
>
> Le 13/10/2021 à 09:39, Christophe Leroy a écrit :
>>
>>
>> Le 13/10/2021 à 09:23, Kees Cook a écrit :
>>> On Mon, Oct 11, 2021 at 05:25:36PM +0200, Christophe Leroy wrote:
>>>> Behind a location, lkdtm_EXEC_RODATA() executes a real function,
>>>> not a copy of do_nothing().
>>>>
>>>> So do it directly instead of using execute_location().
>>>>
>>>> And fix displayed addresses by dereferencing the function descriptors.
>>>>
>>>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>>>> ---
>>>> drivers/misc/lkdtm/perms.c | 9 ++++++++-
>>>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
>>>> index 442d60ed25ef..da16564e1ecd 100644
>>>> --- a/drivers/misc/lkdtm/perms.c
>>>> +++ b/drivers/misc/lkdtm/perms.c
>>>> @@ -153,7 +153,14 @@ void lkdtm_EXEC_VMALLOC(void)
>>>>
>>>> void lkdtm_EXEC_RODATA(void)
>>>> {
>>>> - execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
>>>> + pr_info("attempting ok execution at %px\n",
>>>> + dereference_symbol_descriptor(do_nothing));
>>>> + do_nothing();
>>>> +
>>>> + pr_info("attempting bad execution at %px\n",
>>>> + dereference_symbol_descriptor(lkdtm_rodata_do_nothing));
>>>> + lkdtm_rodata_do_nothing();
>>>> + pr_err("FAIL: func returned\n");
>>>> }
>>>
>>> (In re-reading this more carefully, I see now why kallsyms.h is used
>>> earlier: _function_ vs _symbol_ descriptor.)
>>>
>>> In the next patch:
>>>
>>> static noinline void execute_location(void *dst, bool write)
>>> {
>>> ...
>>> func = setup_function_descriptor(&fdesc, dst);
>>> if (IS_ERR(func))
>>> return;
>>>
>>> pr_info("attempting bad execution at %px\n", dst);
>>> func();
>>> pr_err("FAIL: func returned\n");
>>> }
>>>
>>> What are the conditions for which dereference_symbol_descriptor works
>>> but dereference _function_descriptor doesn't?
>>>
>>
>> When LKDTM is built as a module I guess ?
>>
>
> To be more precise, dereference_symbol_descriptor() calls either
> dereference_kernel_function_descriptor() or
> dereference_module_function_descriptor()
>
> Both functions call dereference_function_descriptor() after checking
> that we want to dereference something that is in the OPD section.
>
> If we call dereference_function_descriptor() directly instead of
> dereference_symbol_descriptor() we skip the range verification and may
> dereference something that is not a function descriptor.
>
> Should we do that ?
>
Indeed we are using it only for well known functions so using
dereference_function_descriptor() is good enough. I'll use that in v2.
next prev parent reply other threads:[~2021-10-13 12:45 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-11 15:25 [PATCH v1 00/10] Fix LKDTM for PPC64/IA64/PARISC Christophe Leroy
2021-10-11 15:25 ` [PATCH v1 01/10] powerpc: Move 'struct ppc64_opd_entry' back into asm/elf.h Christophe Leroy
2021-10-12 7:10 ` Michael Ellerman
2021-10-12 8:02 ` Arnd Bergmann
2021-10-13 6:59 ` Kees Cook
2021-10-11 15:25 ` [PATCH v1 02/10] powerpc: Rename 'funcaddr' to 'addr' in 'struct ppc64_opd_entry' Christophe Leroy
2021-10-13 6:59 ` Kees Cook
2021-10-11 15:25 ` [PATCH v1 03/10] ia64: Rename 'ip' to 'addr' in 'struct fdesc' Christophe Leroy
2021-10-13 6:59 ` Kees Cook
2021-10-11 15:25 ` [PATCH v1 04/10] asm-generic: Use HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR to define associated stubs Christophe Leroy
2021-10-12 6:02 ` Helge Deller
2021-10-12 6:11 ` Christophe Leroy
2021-10-12 6:48 ` Helge Deller
2021-10-13 7:00 ` Kees Cook
2021-10-14 7:20 ` Christophe Leroy
2021-10-11 15:25 ` [PATCH v1 05/10] asm-generic: Define 'funct_descr_t' to commonly describe function descriptors Christophe Leroy
2021-10-13 7:01 ` Kees Cook
2021-10-13 7:23 ` Christophe Leroy
2021-10-13 7:27 ` Kees Cook
2021-10-11 15:25 ` [PATCH v1 06/10] asm-generic: Refactor dereference_[kernel]_function_descriptor() Christophe Leroy
2021-10-13 7:02 ` Kees Cook
2021-10-13 11:20 ` Christophe Leroy
2021-10-13 11:34 ` Arnd Bergmann
2021-10-11 15:25 ` [PATCH v1 07/10] lkdtm: Force do_nothing() out of line Christophe Leroy
2021-10-13 7:02 ` Kees Cook
2021-10-11 15:25 ` [PATCH v1 08/10] lkdtm: Really write into kernel text in WRITE_KERN Christophe Leroy
2021-10-13 7:05 ` Kees Cook
2021-10-13 7:29 ` Christophe Leroy
2021-10-11 15:25 ` [PATCH v1 09/10] lkdtm: Fix lkdtm_EXEC_RODATA() Christophe Leroy
2021-10-13 7:09 ` Kees Cook
2021-10-13 7:35 ` Christophe Leroy
2021-10-13 7:23 ` Kees Cook
2021-10-13 7:39 ` Christophe Leroy
2021-10-13 7:48 ` Christophe Leroy
2021-10-13 12:45 ` Christophe Leroy [this message]
2021-10-11 15:25 ` [PATCH v1 10/10] lkdtm: Fix execute_[user]_location() Christophe Leroy
2021-10-13 7:16 ` Kees Cook
2021-10-13 12:00 ` Christophe Leroy
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