[OpenBIOS] [PATCH] Remove zero page mapping from all architectures to allow detection of NULL pointer dereferences.

[Artyom Tarasenko]

On Tue, Apr 9, 2013 at 9:33 PM, Mark Cave-Ayland
<mark.cave-ayland at ilande.co.uk> wrote:
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland at ilande.co.uk>
> ---
>  openbios-devel/arch/ppc/qemu/ofmem.c        |    7 ++++---
>  openbios-devel/arch/sparc32/lib.c           |    6 +++---
>  openbios-devel/arch/sparc64/ofmem_sparc64.c |    4 ++--
>  3 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/openbios-devel/arch/ppc/qemu/ofmem.c b/openbios-devel/arch/ppc/qemu/ofmem.c
> index 0161a17..429f43b 100644
> --- a/openbios-devel/arch/ppc/qemu/ofmem.c
> +++ b/openbios-devel/arch/ppc/qemu/ofmem.c
> @@ -549,9 +549,10 @@ ofmem_init(void)
>  {
>      ofmem_t *ofmem = ofmem_arch_get_private();
>
> -    ofmem_claim_phys(0, get_ram_bottom(), 0);
> -    ofmem_claim_virt(0, get_ram_bottom(), 0);
> -    ofmem_map(0, 0, get_ram_bottom(), 0);
> +    /* Map the memory (don't map page 0 to allow catching of NULL dereferences) */
> +    ofmem_claim_phys(PAGE_SIZE, get_ram_bottom() - PAGE_SIZE, 0);
> +    ofmem_claim_virt(PAGE_SIZE, get_ram_bottom() - PAGE_SIZE, 0);
> +    ofmem_map(PAGE_SIZE, PAGE_SIZE, get_ram_bottom() - PAGE_SIZE, 0);

You seem not to like my

#define LOWMEM_START PAGE_SIZE

? I think it would have made distinguishing between the page size and
the offset parameters more obvious.

Artyom

>
>      /* Map everything at the top of physical RAM 1:1, minus the OpenBIOS ROM in RAM copy */
>      ofmem_claim_phys(get_ram_top(), get_hash_base() + HASH_SIZE - get_ram_top(), 0);
> diff --git a/openbios-devel/arch/sparc32/lib.c b/openbios-devel/arch/sparc32/lib.c
> index c0df654..4ff3619 100644
> --- a/openbios-devel/arch/sparc32/lib.c
> +++ b/openbios-devel/arch/sparc32/lib.c
> @@ -403,9 +403,9 @@ init_mmu_swift(void)
>      ofmem_arch_map_pages(pa, va, size, ofmem_arch_default_translation_mode(pa));
>      ofmem_map_page_range(pa, va, size, ofmem_arch_default_translation_mode(pa));
>
> -    // 1:1 mapping for RAM
> -    ofmem_arch_map_pages(0, 0, LOWMEMSZ, ofmem_arch_default_translation_mode(0));
> -    ofmem_map_page_range(0, 0, LOWMEMSZ, ofmem_arch_default_translation_mode(0));
> +    // 1:1 mapping for RAM (don't map page 0 to allow catching of NULL dereferences)
> +    ofmem_arch_map_pages(PAGE_SIZE, PAGE_SIZE, LOWMEMSZ - PAGE_SIZE, ofmem_arch_default_translation_mode(0));
> +    ofmem_map_page_range(PAGE_SIZE, PAGE_SIZE, LOWMEMSZ - PAGE_SIZE, ofmem_arch_default_translation_mode(0));
>
>      /*
>       * Flush cache
> diff --git a/openbios-devel/arch/sparc64/ofmem_sparc64.c b/openbios-devel/arch/sparc64/ofmem_sparc64.c
> index 50224e6..ece51f9 100644
> --- a/openbios-devel/arch/sparc64/ofmem_sparc64.c
> +++ b/openbios-devel/arch/sparc64/ofmem_sparc64.c
> @@ -365,8 +365,8 @@ void ofmem_init( void )
>         /* inherit translations set up by entry.S */
>         ofmem_walk_boot_map(remap_page_range);
>
> -        /* Map the memory */
> -        ofmem_map_page_range(0, 0, qemu_mem_size, 0x36);
> +        /* Map the memory (don't map page 0 to allow catching of NULL dereferences) */
> +        ofmem_map_page_range(PAGE_SIZE, PAGE_SIZE, qemu_mem_size - PAGE_SIZE, 0x36);
>
>         if (!(retained->magic == RETAIN_MAGIC)) {
>                 OFMEM_TRACE("ofmem_init: no retained magic found, creating\n");
> --
> 1.7.10.4
>
>
> --
> OpenBIOS                 http://openbios.org/
> Mailinglist:  http://lists.openbios.org/mailman/listinfo
> Free your System - May the Forth be with you



--
Regards,
Artyom Tarasenko

linux/sparc and solaris/sparc under qemu blog:
http://tyom.blogspot.com/search/label/qemu