From: Kees Cook <keescook@chromium.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: linux-arch@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-parisc@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Helge Deller <deller@gmx.de>,
linux-kernel@vger.kernel.org,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
linux-mm@kvack.org, Paul Mackerras <paulus@samba.org>,
Andrew Morton <akpm@linux-foundation.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 13/13] lkdtm: Add a test for function descriptors protection
Date: Fri, 15 Oct 2021 14:35:44 -0700 [thread overview]
Message-ID: <202110151433.6270D717@keescook> (raw)
In-Reply-To: <08a3dfbc55e1c7a0a1917b22f0ca6cabd9895ab2.1634190022.git.christophe.leroy@csgroup.eu>
On Thu, Oct 14, 2021 at 07:50:02AM +0200, Christophe Leroy wrote:
> Add WRITE_OPD to check that you can't modify function
> descriptors.
>
> Gives the following result when function descriptors are
> not protected:
>
> lkdtm: Performing direct entry WRITE_OPD
> lkdtm: attempting bad 16 bytes write at c00000000269b358
> lkdtm: FAIL: survived bad write
> lkdtm: do_nothing was hijacked!
>
> Looks like a standard compiler barrier(); is not enough to force
> GCC to use the modified function descriptor. Add to add a fake empty
> inline assembly to force GCC to reload the function descriptor.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> drivers/misc/lkdtm/core.c | 1 +
> drivers/misc/lkdtm/lkdtm.h | 1 +
> drivers/misc/lkdtm/perms.c | 22 ++++++++++++++++++++++
> 3 files changed, 24 insertions(+)
>
> diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
> index fe6fd34b8caf..de092aa03b5d 100644
> --- a/drivers/misc/lkdtm/core.c
> +++ b/drivers/misc/lkdtm/core.c
> @@ -148,6 +148,7 @@ static const struct crashtype crashtypes[] = {
> CRASHTYPE(WRITE_RO),
> CRASHTYPE(WRITE_RO_AFTER_INIT),
> CRASHTYPE(WRITE_KERN),
> + CRASHTYPE(WRITE_OPD),
> CRASHTYPE(REFCOUNT_INC_OVERFLOW),
> CRASHTYPE(REFCOUNT_ADD_OVERFLOW),
> CRASHTYPE(REFCOUNT_INC_NOT_ZERO_OVERFLOW),
> diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
> index c212a253edde..188bd0fd6575 100644
> --- a/drivers/misc/lkdtm/lkdtm.h
> +++ b/drivers/misc/lkdtm/lkdtm.h
> @@ -105,6 +105,7 @@ void __init lkdtm_perms_init(void);
> void lkdtm_WRITE_RO(void);
> void lkdtm_WRITE_RO_AFTER_INIT(void);
> void lkdtm_WRITE_KERN(void);
> +void lkdtm_WRITE_OPD(void);
> void lkdtm_EXEC_DATA(void);
> void lkdtm_EXEC_STACK(void);
> void lkdtm_EXEC_KMALLOC(void);
> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
> index 96b3ebfcb8ed..3870bc82d40d 100644
> --- a/drivers/misc/lkdtm/perms.c
> +++ b/drivers/misc/lkdtm/perms.c
> @@ -44,6 +44,11 @@ static noinline void do_overwritten(void)
> return;
> }
>
> +static noinline void do_almost_nothing(void)
> +{
> + pr_info("do_nothing was hijacked!\n");
> +}
> +
> static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)
> {
> memcpy(fdesc, do_nothing, sizeof(*fdesc));
> @@ -143,6 +148,23 @@ void lkdtm_WRITE_KERN(void)
> do_overwritten();
> }
>
> +void lkdtm_WRITE_OPD(void)
> +{
> + size_t size = sizeof(func_desc_t);
> + void (*func)(void) = do_nothing;
> +
> + if (!have_function_descriptors()) {
> + pr_info("Platform doesn't have function descriptors.\n");
This should be more explicit ('xfail'):
pr_info("XFAIL: platform doesn't use function descriptors.\n");
> + return;
> + }
> + pr_info("attempting bad %zu bytes write at %px\n", size, do_nothing);
> + memcpy(do_nothing, do_almost_nothing, size);
> + pr_err("FAIL: survived bad write\n");
> +
> + asm("" : "=m"(func));
Since this is a descriptor, I assume no icache flush is needed. Are
function descriptors strictly dcache? (Is anything besides just a
barrier needed?)
> + func();
> +}
> +
> void lkdtm_EXEC_DATA(void)
> {
> execute_location(data_area, CODE_WRITE);
> --
> 2.31.1
>
--
Kees Cook
next prev parent reply other threads:[~2021-10-15 21:36 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-14 5:49 [PATCH v2 00/13] Fix LKDTM for PPC64/IA64/PARISC Christophe Leroy
2021-10-14 5:49 ` [PATCH v2 01/13] powerpc: Move 'struct ppc64_opd_entry' back into asm/elf.h Christophe Leroy
2021-10-14 21:26 ` Daniel Axtens
2021-10-15 5:57 ` Nicholas Piggin
2021-10-14 5:49 ` [PATCH v2 02/13] powerpc: Rename 'funcaddr' to 'addr' in 'struct ppc64_opd_entry' Christophe Leroy
2021-10-14 21:45 ` Daniel Axtens
2021-10-15 4:59 ` Christophe Leroy
2021-10-15 6:01 ` Nicholas Piggin
2021-10-14 5:49 ` [PATCH v2 03/13] powerpc: Remove func_descr_t Christophe Leroy
2021-10-14 22:17 ` Daniel Axtens
2021-10-15 5:19 ` Christophe Leroy
2021-10-15 6:11 ` Nicholas Piggin
2021-10-14 5:49 ` [PATCH v2 04/13] powerpc: Prepare func_desc_t for refactorisation Christophe Leroy
2021-10-14 5:49 ` [PATCH v2 05/13] ia64: Rename 'ip' to 'addr' in 'struct fdesc' Christophe Leroy
2021-10-14 5:49 ` [PATCH v2 06/13] asm-generic: Use HAVE_FUNCTION_DESCRIPTORS to define associated stubs Christophe Leroy
2021-10-15 6:16 ` Nicholas Piggin
2021-10-15 6:24 ` Christophe Leroy
2021-10-15 8:02 ` Nicholas Piggin
2021-10-15 11:52 ` Nicholas Piggin
2021-10-14 5:49 ` [PATCH v2 07/13] asm-generic: Define 'func_desc_t' to commonly describe function descriptors Christophe Leroy
2021-10-14 6:52 ` Arnd Bergmann
2021-10-14 5:49 ` [PATCH v2 08/13] asm-generic: Refactor dereference_[kernel]_function_descriptor() Christophe Leroy
2021-10-15 7:00 ` Nicholas Piggin
2021-10-14 5:49 ` [PATCH v2 09/13] lkdtm: Force do_nothing() out of line Christophe Leroy
2021-10-14 5:49 ` [PATCH v2 10/13] lkdtm: Really write into kernel text in WRITE_KERN Christophe Leroy
2021-10-14 5:50 ` [PATCH v2 11/13] lkdtm: Fix lkdtm_EXEC_RODATA() Christophe Leroy
2021-10-15 21:32 ` Kees Cook
2021-10-16 6:41 ` Christophe Leroy
2021-10-17 7:50 ` Christophe Leroy
2021-10-14 5:50 ` [PATCH v2 12/13] lkdtm: Fix execute_[user]_location() Christophe Leroy
2021-10-15 21:31 ` Kees Cook
2021-10-16 6:42 ` Christophe Leroy
2021-11-16 15:07 ` Christophe Leroy
2021-10-14 5:50 ` [PATCH v2 13/13] lkdtm: Add a test for function descriptors protection Christophe Leroy
2021-10-15 21:35 ` Kees Cook [this message]
2021-10-16 6:28 ` Christophe Leroy
2021-10-14 21:35 ` [PATCH v2 00/13] Fix LKDTM for PPC64/IA64/PARISC Daniel Axtens
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