From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9192CC433EF for ; Sat, 16 Oct 2021 06:28:51 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AD8B061108 for ; Sat, 16 Oct 2021 06:28:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org AD8B061108 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4HWYB850Wpz3cLc for ; Sat, 16 Oct 2021 17:28:48 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=csgroup.eu (client-ip=93.17.235.10; helo=pegase2.c-s.fr; envelope-from=christophe.leroy@csgroup.eu; receiver=) Received: from pegase2.c-s.fr (pegase2.c-s.fr [93.17.235.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4HWY9b2B9Fz2xt0 for ; Sat, 16 Oct 2021 17:28:16 +1100 (AEDT) Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4HWY9Q53xqz9sSL; Sat, 16 Oct 2021 08:28:10 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from pegase2.c-s.fr ([172.26.127.65]) by localhost (pegase2.c-s.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id k-Fz29ksyfF0; Sat, 16 Oct 2021 08:28:10 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase2.c-s.fr (Postfix) with ESMTP id 4HWY9Q3nwlz9sSH; Sat, 16 Oct 2021 08:28:10 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 5E0778B765; Sat, 16 Oct 2021 08:28:10 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id 4rYxWz_zPmYc; Sat, 16 Oct 2021 08:28:10 +0200 (CEST) Received: from PO20335.IDSI0.si.c-s.fr (unknown [192.168.203.36]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 215348B763; Sat, 16 Oct 2021 08:28:09 +0200 (CEST) Subject: Re: [PATCH v2 13/13] lkdtm: Add a test for function descriptors protection To: Kees Cook References: <08a3dfbc55e1c7a0a1917b22f0ca6cabd9895ab2.1634190022.git.christophe.leroy@csgroup.eu> <202110151433.6270D717@keescook> From: Christophe Leroy Message-ID: Date: Sat, 16 Oct 2021 08:28:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <202110151433.6270D717@keescook> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr-FR Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, Arnd Bergmann , Greg Kroah-Hartman , Helge Deller , linux-kernel@vger.kernel.org, "James E.J. Bottomley" , linux-mm@kvack.org, Paul Mackerras , Andrew Morton , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 15/10/2021 à 23:35, Kees Cook a écrit : > 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 >> --- >> 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"); Ok > >> + 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?) No flush is needed, the code just loads the function address from memory into CTR, loads R2 and branch to CTR: 19c: e9 21 00 70 ld r9,112(r1) 1a0: e9 49 00 00 ld r10,0(r9) 1a4: 7d 49 03 a6 mtctr r10 1a8: e8 49 00 08 ld r2,8(r9) 1ac: 4e 80 04 21 bctrl > >> + func(); >> +} >> + >> void lkdtm_EXEC_DATA(void) >> { >> execute_location(data_area, CODE_WRITE); >> -- >> 2.31.1 >> >