linux-kernel - Re: [PATCH v4 3/3] MIPS: set stack/data protection as non-executable

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Message-ID: <55C2A28C.7000809@caviumnetworks.com>
Date:	Wed, 5 Aug 2015 16:55:56 -0700
From:	David Daney <ddaney@...iumnetworks.com>
To:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
CC:	<daniel.sanders@...tec.com>, <linux-mips@...ux-mips.org>,
	<cernekee@...il.com>, <Zubair.Kakakhel@...tec.com>,
	<geert+renesas@...der.be>, <david.daney@...ium.com>,
	<peterz@...radead.org>, <heiko.carstens@...ibm.com>,
	<paul.gortmaker@...driver.com>, <behanw@...verseincode.com>,
	<macro@...ux-mips.org>, <cl@...ux.com>, <pkarat@...sta.com>,
	<linux@...ck-us.net>, <tkhai@...dex.ru>, <james.hogan@...tec.com>,
	<alexinbeijing@...il.com>, <rusty@...tcorp.com.au>,
	<Steven.Hill@...tec.com>, <lars.persson@...s.com>,
	<aleksey.makarov@...iga.com>, <paul.burton@...tec.com>,
	<linux-kernel@...r.kernel.org>, <ralf@...ux-mips.org>,
	<luto@...capital.net>, <dahi@...ux.vnet.ibm.com>,
	<markos.chandras@...tec.com>, <eunb.song@...sung.com>,
	<kumba@...too.org>
Subject: Re: [PATCH v4 3/3] MIPS: set stack/data protection as non-executable

On 08/05/2015 04:49 PM, Leonid Yegoshin wrote:
> This is a last step of 3 patches which shift FPU emulation out of
> stack into protected area. So, it disables a default executable stack.
>

NAK.

You cannot change the default.

If you want a non-executable stack, the program has to request it with 
the proper annotations in its ELF file.

David Daney.


> Additionally, it sets a default data area non-executable protection.
>
> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
> ---
>   arch/mips/include/asm/page.h |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/mips/include/asm/page.h b/arch/mips/include/asm/page.h
> index 89dd7fed1a57..0b6cec4a1b80 100644
> --- a/arch/mips/include/asm/page.h
> +++ b/arch/mips/include/asm/page.h
> @@ -228,7 +228,7 @@ extern int __virt_addr_valid(const volatile void *kaddr);
>   #define virt_addr_valid(kaddr)						\
>   	__virt_addr_valid((const volatile void *) (kaddr))
>
> -#define VM_DATA_DEFAULT_FLAGS	(VM_READ | VM_WRITE | VM_EXEC | \
> +#define VM_DATA_DEFAULT_FLAGS	(VM_READ | VM_WRITE | \
>   				 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
>
>   #define UNCAC_ADDR(addr)	((addr) - PAGE_OFFSET + UNCAC_BASE)
>

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