linux-kernel - RE: [PATCH 1/3] ARM: Define KERNEL_START and KERNEL

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Message-ID: <SG2PR06MB116569D2A9756BE11131CB4B8A820@SG2PR06MB1165.apcprd06.prod.outlook.com>
Date:   Tue, 6 Dec 2016 22:43:40 +0000
From:   Chris Brandt <Chris.Brandt@...esas.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
CC:     "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
        "panand@...hat.com" <panand@...hat.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "jonathan.austin@....com" <jonathan.austin@....com>,
        "pawel.moll@....com" <pawel.moll@....com>,
        "vladimir.murzin@....com" <vladimir.murzin@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "matt@...eblueprint.co.uk" <matt@...eblueprint.co.uk>,
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        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "ben@...adent.org.uk" <ben@...adent.org.uk>,
        "js07.lee@...sung.com" <js07.lee@...sung.com>,
        "stefan@...er.ch" <stefan@...er.ch>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/3] ARM: Define KERNEL_START and KERNEL_END

On 12/6/2016, Florian Fainelli wrote:
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 4001dd15818d..18ef688a796e 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -1437,12 +1437,8 @@ static void __init kmap_init(void)
>  static void __init map_lowmem(void)
>  {
>  	struct memblock_region *reg;
> -#ifdef CONFIG_XIP_KERNEL
> -	phys_addr_t kernel_x_start = round_down(__pa(_sdata), SECTION_SIZE);
> -#else
> -	phys_addr_t kernel_x_start = round_down(__pa(_stext), SECTION_SIZE);
> -#endif
> -	phys_addr_t kernel_x_end = round_up(__pa(__init_end), SECTION_SIZE);
> +	phys_addr_t kernel_x_start = round_down(__pa(KERNEL_START),
> SECTION_SIZE);
> +	phys_addr_t kernel_x_end = round_down(__pa(_end), SECTION_SIZE);

Why are you changing the end of executable kernel (hence the 'x' in
kernel_x_end) from __init_end to _end which basically maps the entire
kernel image including text and data?

Doing so would then change data from MT_MEMORY_RW into MT_MEMORY_RWX.

I would think it would create some type of security risk to allow
data to be executable.