linux-kernel - Re: [PATCH v3 3/3] MIPS: set stack/data protection as non-executable

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Date:	Fri, 5 Dec 2014 10:51:15 -0800
From:	Kees Cook <keescook@...omium.org>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	Zubair.Kakakhel@...tec.com, geert+renesas@...der.be,
	david.daney@...ium.com, Peter Zijlstra <peterz@...radead.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	davidlohr@...com, "Maciej W. Rozycki" <macro@...ux-mips.org>,
	chenhc@...ote.com, cl@...ux.com, Ingo Molnar <mingo@...nel.org>,
	Richard Weinberger <richard@....at>,
	Rafał Miłecki <zajec5@...il.com>,
	James Hogan <james.hogan@...tec.com>,
	Tejun Heo <tj@...nel.org>, alex@...x-smith.me.uk,
	Paolo Bonzini <pbonzini@...hat.com>,
	John Crispin <blogic@...nwrt.org>,
	Paul Burton <paul.burton@...tec.com>, qais.yousef@...tec.com,
	LKML <linux-kernel@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Markos Chandras <markos.chandras@...tec.com>,
	dengcheng.zhu@...tec.com, manuel.lauss@...il.com,
	lars.persson@...s.com
Subject: Re: [PATCH v3 3/3] MIPS: set stack/data protection as non-executable

On Fri, Dec 5, 2014 at 9:28 AM, David Daney <ddaney.cavm@...il.com> wrote:
> On 12/02/2014 05:58 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.
>>
>> Additionally, it sets a default data area non-executable protection.
>>
>> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
>
>
> NAK!
>
> Some programs require an executable stack, this patch will break them.

Have you tested this?

> You can only select a non-executable stack in response to PT_GNU_STACK
> program headers in the ELF file of the executable program.

This is already handled by fs/binfmt_elf.c. It does the parsing of the
PT_GNU_STACK needs, and sets up the stack flags appropriately. All the
change to VM_DATA_DEFAULT_FLAGS does is make sure that EXSTACK_DEFAULT
now means no VM_EXEC by default. If PT_GNU_STACK requires it, it gets
added back in.

-Kees

>
> David Daney
>
>
>
>> ---
>>   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 3be81803595d..d49ba81cb4ed 100644
>> --- a/arch/mips/include/asm/page.h
>> +++ b/arch/mips/include/asm/page.h
>> @@ -230,7 +230,7 @@ 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)
>>
>>
>>
>>
>



-- 
Kees Cook
Chrome OS Security
--
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