From: Sascha Hauer <s.hauer@pengutronix.de>
To: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH 1/1] arm: mmu: catch NULL pointer dereferences
Date: Mon, 2 Sep 2013 11:05:23 +0200 [thread overview]
Message-ID: <20130902090523.GT30088@pengutronix.de> (raw)
In-Reply-To: <1377964462-10387-1-git-send-email-plagnioj@jcrosoft.com>
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 <plagnioj@jcrosoft.com>
> ---
> 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
--
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next prev parent reply other threads:[~2013-09-02 9:05 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-31 15:54 Jean-Christophe PLAGNIOL-VILLARD
2013-09-02 9:05 ` Sascha Hauer [this message]
2013-09-02 10:24 ` Jean-Christophe PLAGNIOL-VILLARD
2013-09-04 7:07 ` Sascha Hauer
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