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Wed, 26 Feb 2020 08:19:25 +0100 (CET) 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 jMZVJHRWNoTy; Wed, 26 Feb 2020 08:19:25 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id E6E668B776; Wed, 26 Feb 2020 08:19:24 +0100 (CET) Subject: Re: [PATCH v4 8/8] powerpc/mm: Disable set_memory() routines when strict RWX isn't enabled To: Russell Currey , linuxppc-dev@lists.ozlabs.org References: <20200226062403.63790-1-ruscur@russell.cc> <20200226062403.63790-9-ruscur@russell.cc> From: Christophe Leroy Message-ID: <2a9988ec-c115-8fe8-4c68-82eb2fa43d6b@c-s.fr> Date: Wed, 26 Feb 2020 08:19:19 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200226062403.63790-9-ruscur@russell.cc> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: 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: ajd@linux.ibm.com, kernel-hardening@lists.openwall.com, npiggin@gmail.com, joel@jms.id.au, Jordan Niethe , dja@axtens.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 26/02/2020 à 07:24, Russell Currey a écrit : > There are a couple of reasons that the set_memory() functions are > problematic when STRICT_KERNEL_RWX isn't enabled: > > - The linear mapping is a different size and apply_to_page_range() > may modify a giant section, breaking everything I don't understand. > - patch_instruction() doesn't know to work around a page being marked > RO, and will subsequently crash Is patch_instruction() involved at all ? > > The latter can be replicated by building a kernel with the set_memory() > patches but with STRICT_KERNEL_RWX off and running ftracetest. > > Reported-by: Jordan Niethe > Signed-off-by: Russell Currey > --- > v4: new > > arch/powerpc/mm/pageattr.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/mm/pageattr.c b/arch/powerpc/mm/pageattr.c > index ee6b5e3b7604..ff111930cf5e 100644 > --- a/arch/powerpc/mm/pageattr.c > +++ b/arch/powerpc/mm/pageattr.c > @@ -96,12 +96,17 @@ static int set_page_attr(pte_t *ptep, unsigned long addr, void *data) > > int set_memory_attr(unsigned long addr, int numpages, pgprot_t prot) Isn't it change_memory_attr() that is a problem for you ? > { > - unsigned long start = ALIGN_DOWN(addr, PAGE_SIZE); > - unsigned long sz = numpages * PAGE_SIZE; > + unsigned long start, size; > + > + if (!IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) > + return 0; Doing this you break patch 7: mark_initmem_nx() is called regardless of CONFIG_STRICT_KERNEL_RWX __kernel_map_pages() depends on CONFIG_DEBUG_PAGEALLOC which doesn't depend on CONFIG_STRICT_KERNEL_RWX > > if (!numpages) > return 0; > > - return apply_to_page_range(&init_mm, start, sz, set_page_attr, > + start = ALIGN_DOWN(addr, PAGE_SIZE); > + size = numpages * PAGE_SIZE; > + > + return apply_to_page_range(&init_mm, start, size, set_page_attr, You don't need to move start and size calculation and change the above. > (void *)pgprot_val(prot)); > } > Christophe