Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1201344 > unrolled thread

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

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  [PATCH v4 3/3] MIPS: set stack/data protection as non-executable Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-08-06 01:50 +0200
    Re: [PATCH v4 3/3] MIPS: set stack/data protection as non-executable Paul Burton <paul.burton@imgtec.com> - 2015-08-06 02:00 +0200
      Re: [PATCH v4 3/3] MIPS: set stack/data protection as non-executable Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-08-06 02:10 +0200
        Re: [PATCH v4 3/3] MIPS: set stack/data protection as non-executable Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-08-06 02:30 +0200
          Re: [PATCH v4 3/3] MIPS: set stack/data protection as non-executable Paul Burton <paul.burton@imgtec.com> - 2015-08-06 02:50 +0200
          Re: [PATCH v4 3/3] MIPS: set stack/data protection as non-executable Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-08-06 02:50 +0200

#1201344 — [PATCH v4 3/3] MIPS: set stack/data protection as non-executable

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@imgtec.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)

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1201348

On Wed, Aug 05, 2015 at 04:49:36PM -0700, 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@imgtec.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)
> 

Hi Leonid,

As was pointed out last time you posted this, it breaks backwards
compatibility with userland & thus cannot be applied. We should only be
changing executability of memory in the presence of a PT_GNU_STACK
header indicating that it's safe to do so, with cooperation from the
toolchain team to begin emitting it for MIPS. See the way ARM did it, or
the patches I've posted for this in the past.

Thanks,
    Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1201353

On 08/05/2015 04:55 PM, Paul Burton wrote:
>
>
> As was pointed out last time you posted this, it breaks backwards
> compatibility with userland & thus cannot be applied.

Never observed since first version.

In other side, the problem with apps like ssh_keygen is observed in 
absence of executable stack protection.

- Leonid.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1201367

On 08/05/2015 05:14 PM, David Daney wrote:
> On 08/05/2015 05:06 PM, Leonid Yegoshin wrote:
>> On 08/05/2015 04:55 PM, Paul Burton wrote:
>>>
>>>
>>> As was pointed out last time you posted this, it breaks backwards
>>> compatibility with userland & thus cannot be applied.
>>
>> Never observed since first version.
>>
>> In other side, the problem with apps like ssh_keygen is observed in
>> absence of executable stack protection.
>
> You cannot change the default.
>
> If your ssh_keygen is broken, get a working version.

It is actually any application which requests non-executable stack 
protection and needs some emulation BEFORE GLIBC cancels that 
non-executable stack protection due to libraries.

If you build all libraries with PT_GNU_STACK 'non-executable' and use 
application with the same protection then you can't emulate even a 
single instruction - it crashes immediately. So, it is not a bad 
application, it is a bad choice for emulation space in past.

>
> I have never had a problem running ssh_keygen (on platforms requiring 
> emulation).

Create a buildroot FS with PT_GNU_STACK 'non-executable' libraries. Then 
run ssh_keygen on CPU without FPU and look.

You also may try to run MIPS R2 Debian on MIPS R6 CPU, and see a 
spectacular failure of ssh_keygen (it tries to emulate MIPS R2 
instruction before first library is loaded and that fails due to 
non-executable stack protection.

- Leonid.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1201372

On Wed, Aug 05, 2015 at 05:23:55PM -0700, Leonid Yegoshin wrote:
> It is actually any application which requests non-executable stack
> protection and needs some emulation BEFORE GLIBC cancels that non-executable
> stack protection due to libraries.
> 
> If you build all libraries with PT_GNU_STACK 'non-executable' and use
> application with the same protection then you can't emulate even a single
> instruction - it crashes immediately. So, it is not a bad application, it is
> a bad choice for emulation space in past.

...snip...

> Create a buildroot FS with PT_GNU_STACK 'non-executable' libraries. Then run
> ssh_keygen on CPU without FPU and look.
> 
> You also may try to run MIPS R2 Debian on MIPS R6 CPU, and see a spectacular
> failure of ssh_keygen (it tries to emulate MIPS R2 instruction before first
> library is loaded and that fails due to non-executable stack protection.

All of that sounds like perfectly valid reasons to move the FP branch
delay emulation away from using the stack, which we absolutely do need
to do. They do not however justify changing the default flags & breaking
backwards compatibility.

Thanks,
    Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1201373

On 08/05/2015 05:37 PM, David Daney wrote:
> This just means that your userspace is broken.
>
> If GLibC cannot do the right thing then it should be fixed.

Let's skip this until you explain how to create a fully 
non-executable-stack process. GLIBC people is ready to do something but 
after we remove emulation from stack.

>
>
> You cannot change the default setting for executable stack just 
> because you have created a broken userspace.

Please give me at least one example, one existing application which 
would suffer.

I remember that people already wrote here that this kind of apps (which 
is based on eXecutable stack and doesn't announce it in PT_GNU_STACK) 
need to be eliminated.

>
> The ability of legacy userspace to continue functioning cannot be 
> sacrificed.
>

Not at any price.

However, this switch is a separate patch from others. It can be not 
applied or it can be applied, depending from prevailing mind - what is 
more significant, some (unknown) app or non-executable stack protection.

- Leonid.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web