From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:6f8:1178:4:290:27ff:fe1d:cc33]) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1VGQ4v-0002T5-SJ for barebox@lists.infradead.org; Mon, 02 Sep 2013 09:05:46 +0000 Date: Mon, 2 Sep 2013 11:05:23 +0200 From: Sascha Hauer Message-ID: <20130902090523.GT30088@pengutronix.de> References: <1377964462-10387-1-git-send-email-plagnioj@jcrosoft.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1377964462-10387-1-git-send-email-plagnioj@jcrosoft.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH 1/1] arm: mmu: catch NULL pointer dereferences To: Jean-Christophe PLAGNIOL-VILLARD Cc: barebox@lists.infradead.org On Sat, Aug 31, 2013 at 05:54:22PM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote: > For high vectors if memory start at 0x0. We have to > live without being able to catch NULL pointer dereferences. > > Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD > --- > arch/arm/cpu/mmu.c | 27 +++++++++++++++++++++------ > 1 file changed, 21 insertions(+), 6 deletions(-) > > diff --git a/arch/arm/cpu/mmu.c b/arch/arm/cpu/mmu.c > index e3ea3b6..2e69b16 100644 > --- a/arch/arm/cpu/mmu.c > +++ b/arch/arm/cpu/mmu.c > @@ -218,9 +218,9 @@ static int arm_mmu_remap_sdram(struct memory_bank *bank) > /* > * Map vectors and zero page > */ > -static void vectors_init(void) > +static void vectors_init(bool zero_valid_addr) > { > - u32 *exc, *zero = NULL; > + u32 *exc; > void *vectors; > u32 cr; > > @@ -235,10 +235,19 @@ static void vectors_init(void) > * page table for the high vectors and zero page > */ > exc = arm_create_pte(0xfff00000); > - zero = arm_create_pte(0x0); > > - /* Set the zero page to faulting */ > - zero[0] = 0; > + /* > + * Memory start at 0x0. We have to > + * live without being able to catch NULL pointer dereferences > + */ > + if (!zero_valid_addr) { > + u32 *zero = NULL; > + > + zero = arm_create_pte(0x0); > + > + /* Set the zero page to faulting */ > + zero[0] = 0; > + } > } else { > /* > * Otherwise map the vectors to the zero page. We have to > @@ -267,6 +276,7 @@ static int mmu_init(void) > { > struct memory_bank *bank; > int i; > + bool is_start_zero = 0; > > arm_set_cache_functions(); > > @@ -303,7 +313,12 @@ static int mmu_init(void) > create_sections(0, 0, PAGE_SIZE, PMD_SECT_AP_WRITE | PMD_SECT_AP_READ | > PMD_TYPE_SECT); > > - vectors_init(); > + for_each_memory_bank(bank) { > + if (bank->start == 0x0) > + is_start_zero = 1; > + } > + > + vectors_init(is_start_zero); Why not add the check to vectors_init() instead of passing this as argument? I must say I'm not entirely happy with this approach. Being able to catch NULL pointer derefs is really a good thing. When exactly does the faulting zero SDRAM page become a problem for you? obviously something like cp /somehing /dev/ram0 does not work. Some care must probably be taken when setting up the kernel parameters. Are these the problems or is there something else? Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox