linux-kernel - Re: [PATCH v4] ARM: mm: fix reporting of read-only PMD bits

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Date:	Fri, 28 Mar 2014 11:45:41 -0700
From:	Kees Cook <keescook@...gle.com>
To:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Cc:	Russell King <linux@....linux.org.uk>,
	Rob Herring <robherring2@...il.com>,
	Olof Johansson <olof@...om.net>,
	Catalin Marinas <catalin.marinas@....com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Steve Capper <steve.capper@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] ARM: mm: fix reporting of read-only PMD bits

On Sat, Mar 22, 2014 at 9:20 PM, Kees Cook <keescook@...omium.org> wrote:
> On non-LPAE ARMv6+, read-only PMD bits are defined with the combination
> "PMD_SECT_APX | PMD_SECT_AP_WRITE". Adjusted the bit masks to correctly
> report this.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v4:
>  - clean up defines for CPU versions; Rob Herring.
> v3:
>  - check for pre-v6 CPUs on the page table report.
> v2:
>  - reorder bits, suggested by Olof.

Can anyone give this a test or ack? I've done build tests for all CPU
combinations, and runtime tests on v6 and LPAE.

Thanks!

-Kees

> ---
>  arch/arm/mm/dump.c |   47 ++++++++++++++++++++++++++++++++---------------
>  1 file changed, 32 insertions(+), 15 deletions(-)
>
> diff --git a/arch/arm/mm/dump.c b/arch/arm/mm/dump.c
> index ef69152f9b52..c508f41a43bc 100644
> --- a/arch/arm/mm/dump.c
> +++ b/arch/arm/mm/dump.c
> @@ -120,34 +120,51 @@ static const struct prot_bits pte_bits[] = {
>  };
>
>  static const struct prot_bits section_bits[] = {
> -#ifndef CONFIG_ARM_LPAE
> -       /* These are approximate */
> +#ifdef CONFIG_ARM_LPAE
> +       {
> +               .mask   = PMD_SECT_USER,
> +               .val    = PMD_SECT_USER,
> +               .set    = "USR",
> +       }, {
> +               .mask   = PMD_SECT_RDONLY,
> +               .val    = PMD_SECT_RDONLY,
> +               .set    = "ro",
> +               .clear  = "RW",
> +#elif __LINUX_ARM_ARCH__ >= 6
>         {
> -               .mask   = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> -               .val    = 0,
> +               .mask   = PMD_SECT_APX | PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .val    = PMD_SECT_APX | PMD_SECT_AP_WRITE,
>                 .set    = "    ro",
>         }, {
> -               .mask   = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .mask   = PMD_SECT_APX | PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
>                 .val    = PMD_SECT_AP_WRITE,
>                 .set    = "    RW",
>         }, {
> -               .mask   = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .mask   = PMD_SECT_APX | PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
>                 .val    = PMD_SECT_AP_READ,
>                 .set    = "USR ro",
>         }, {
> -               .mask   = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .mask   = PMD_SECT_APX | PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
>                 .val    = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
>                 .set    = "USR RW",
> -#else
> +#else /* ARMv4/ARMv5  */
> +       /* These are approximate */
>         {
> -               .mask   = PMD_SECT_USER,
> -               .val    = PMD_SECT_USER,
> -               .set    = "USR",
> +               .mask   = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .val    = 0,
> +               .set    = "    ro",
>         }, {
> -               .mask   = PMD_SECT_RDONLY,
> -               .val    = PMD_SECT_RDONLY,
> -               .set    = "ro",
> -               .clear  = "RW",
> +               .mask   = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .val    = PMD_SECT_AP_WRITE,
> +               .set    = "    RW",
> +       }, {
> +               .mask   = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .val    = PMD_SECT_AP_READ,
> +               .set    = "USR ro",
> +       }, {
> +               .mask   = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .val    = PMD_SECT_AP_READ | PMD_SECT_AP_WRITE,
> +               .set    = "USR RW",
>  #endif
>         }, {
>                 .mask   = PMD_SECT_XN,
> --
> 1.7.9.5
>
>
> --
> Kees Cook
> Chrome OS Security



-- 
Kees Cook
Chrome OS Security
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