[PATCH] arm64: trap illegal translations in __virt_to_phys()

[PATCH] arm64: trap illegal translations in __virt_to_phys()

[Miles Chen]

Current __virt_to_phys() only print warning messages for non-linear
addresses. It's hard to catch all warnings by those messages. So add a
VIRTUAL_BUG_ON() to trap all non-linear and non-symbol addresses
(e.g., stack addresses)

Tested by pass stack addresses and symbol addresses to __pa(). Result:
stack addresses: kernel BUG()
symbol addresses: kernel warning message

Maybe we should trap all non-linear address translations in the future.

Signed-off-by: Miles Chen <miles.chen@mediatek.com>
---
 arch/arm64/mm/physaddr.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
index 67a9ba9eaa96..f6b935dad19c 100644
--- a/arch/arm64/mm/physaddr.c
+++ b/arch/arm64/mm/physaddr.c
@@ -14,6 +14,11 @@ phys_addr_t __virt_to_phys(unsigned long x)
 	      (void *)x,
 	      (void *)x);
 
+	/* trap all non-linear and non-symbol addresses */
+	VIRTUAL_BUG_ON(!__is_lm_address(x) &&
+			(x < (unsigned long)KERNEL_START ||
+			 x > (unsigned long)KERNEL_END));
+
 	return __virt_to_phys_nodebug(x);
 }
 EXPORT_SYMBOL(__virt_to_phys);
-- 
2.18.0


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH] arm64: trap illegal translations in __virt_to_phys()

[Mark Rutland]

On Mon, Jan 07, 2019 at 07:21:20PM +0800, Miles Chen wrote:
> Current __virt_to_phys() only print warning messages for non-linear
> addresses. It's hard to catch all warnings by those messages.

Why? Are you seeing a large number of warnings somewhere?

> So add a VIRTUAL_BUG_ON() to trap all non-linear and non-symbol
> addresses (e.g., stack addresses)
> 
> Tested by pass stack addresses and symbol addresses to __pa(). Result:
> stack addresses: kernel BUG()

Either:

* Stacks are vmap'd, and __is_lm_address(stack_addr) is false. We'll
  produce a WARNING() today (and return a junk physical address).

* Stacks are linear mapped, and cannot be distinguished from other
  linear mapped addresses. The physical address will be valid.

... so I don't understand why you need to change this.

> symbol addresses: kernel warning message

That should already be the case today, since the kernel image is mapped
separately from the linear map, so __is_lm_address(symbol_addr) should
be false.

> 
> Maybe we should trap all non-linear address translations in the future.
> 
> Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> ---
>  arch/arm64/mm/physaddr.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
> index 67a9ba9eaa96..f6b935dad19c 100644
> --- a/arch/arm64/mm/physaddr.c
> +++ b/arch/arm64/mm/physaddr.c
> @@ -14,6 +14,11 @@ phys_addr_t __virt_to_phys(unsigned long x)
>  	      (void *)x,
>  	      (void *)x);
>  
> +	/* trap all non-linear and non-symbol addresses */
> +	VIRTUAL_BUG_ON(!__is_lm_address(x) &&
> +			(x < (unsigned long)KERNEL_START ||
> +			 x > (unsigned long)KERNEL_END));

The KERNEL_START and KERNEL_END definitions refer to the kernel image,
not the linear map, so it doesn't make any sense to permit those here.

It is *not* valid to call __virt_to_phys() with a symbol address. We
only support those in __virt_to_phys_nodebug() so that broken code has a
chance of stumbling on.

If you want the kernel to die immediately when it hits a warning here,
please set panic_on_warn.

Thanks,
Mark.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH] arm64: trap illegal translations in __virt_to_phys()

[Miles Chen]

On Mon, 2019-01-07 at 15:00 +0000, Mark Rutland wrote:
> On Mon, Jan 07, 2019 at 07:21:20PM +0800, Miles Chen wrote:
> > Current __virt_to_phys() only print warning messages for non-linear
> > addresses. It's hard to catch all warnings by those messages.
> 
> Why? Are you seeing a large number of warnings somewhere?

Official kernel works fine. I saw some cases in our internal branch and
we're fixing them.

> 
> > So add a VIRTUAL_BUG_ON() to trap all non-linear and non-symbol
> > addresses (e.g., stack addresses)
> > 
> > Tested by pass stack addresses and symbol addresses to __pa(). Result:
> > stack addresses: kernel BUG()
> 
> Either:
> 
> * Stacks are vmap'd, and __is_lm_address(stack_addr) is false. We'll
>   produce a WARNING() today (and return a junk physical address).
> 
> * Stacks are linear mapped, and cannot be distinguished from other
>   linear mapped addresses. The physical address will be valid.
> 
> ... so I don't understand why you need to change this.

For the first case: for vmap'd stack, __pa() returns a junk
physical address and it might be easier to debug this incorrect address
translation by a BUG() call instead of monitoring the warning log.

Like __phys_addr_symbol() does. __phys_addr_symbol() uses
VIRTUAL_BUG_ON() for non symbol addresses.

> 
> > symbol addresses: kernel warning message
> 
> That should already be the case today, since the kernel image is mapped
> separately from the linear map, so __is_lm_address(symbol_addr) should
> be false.
> 
> > 
> > Maybe we should trap all non-linear address translations in the future.
> > 
> > Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> > ---
> >  arch/arm64/mm/physaddr.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
> > index 67a9ba9eaa96..f6b935dad19c 100644
> > --- a/arch/arm64/mm/physaddr.c
> > +++ b/arch/arm64/mm/physaddr.c
> > @@ -14,6 +14,11 @@ phys_addr_t __virt_to_phys(unsigned long x)
> >  	      (void *)x,
> >  	      (void *)x);
> >  
> > +	/* trap all non-linear and non-symbol addresses */
> > +	VIRTUAL_BUG_ON(!__is_lm_address(x) &&
> > +			(x < (unsigned long)KERNEL_START ||
> > +			 x > (unsigned long)KERNEL_END));
> 
> The KERNEL_START and KERNEL_END definitions refer to the kernel image,
> not the linear map, so it doesn't make any sense to permit those here.
> 
> It is *not* valid to call __virt_to_phys() with a symbol address. We
> only support those in __virt_to_phys_nodebug() so that broken code has a
> chance of stumbling on.
> 
> If you want the kernel to die immediately when it hits a warning here,
> please set panic_on_warn.
> 
> Thanks,
> Mark.



_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH] arm64: trap illegal translations in __virt_to_phys()

[Mark Rutland]

On Tue, Jan 08, 2019 at 11:24:43AM +0800, Miles Chen wrote:
> On Mon, 2019-01-07 at 15:00 +0000, Mark Rutland wrote:
> > On Mon, Jan 07, 2019 at 07:21:20PM +0800, Miles Chen wrote:
> > > Current __virt_to_phys() only print warning messages for non-linear
> > > addresses. It's hard to catch all warnings by those messages.
> > 
> > Why? Are you seeing a large number of warnings somewhere?
> 
> Official kernel works fine. I saw some cases in our internal branch and
> we're fixing them.
> 
> > 
> > > So add a VIRTUAL_BUG_ON() to trap all non-linear and non-symbol
> > > addresses (e.g., stack addresses)
> > > 
> > > Tested by pass stack addresses and symbol addresses to __pa(). Result:
> > > stack addresses: kernel BUG()
> > 
> > Either:
> > 
> > * Stacks are vmap'd, and __is_lm_address(stack_addr) is false. We'll
> >   produce a WARNING() today (and return a junk physical address).
> > 
> > * Stacks are linear mapped, and cannot be distinguished from other
> >   linear mapped addresses. The physical address will be valid.
> > 
> > ... so I don't understand why you need to change this.
> 
> For the first case: for vmap'd stack, __pa() returns a junk
> physical address and it might be easier to debug this incorrect address
> translation by a BUG() call instead of monitoring the warning log.

I think that's an argument for upgrading the existing WARN() to a BUG(),
rather than adding a separate VIRTUAL_BUG_ON().

However, there are cases where the junk physical address is not used to
perform an access, and the WARN() is more helpful.

You can set panic_on_warn to get an immediate panic() when the WARN()
fires. Is there some reason that approach doesn't work for you?

Thanks,
Mark.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH] arm64: trap illegal translations in __virt_to_phys()

[Miles Chen]

On Tue, 2019-01-08 at 12:14 +0000, Mark Rutland wrote:
> On Tue, Jan 08, 2019 at 11:24:43AM +0800, Miles Chen wrote:
> > On Mon, 2019-01-07 at 15:00 +0000, Mark Rutland wrote:
> > > On Mon, Jan 07, 2019 at 07:21:20PM +0800, Miles Chen wrote:
> > > > Current __virt_to_phys() only print warning messages for non-linear
> > > > addresses. It's hard to catch all warnings by those messages.
> > > 
> > > Why? Are you seeing a large number of warnings somewhere?
> > 
> > Official kernel works fine. I saw some cases in our internal branch and
> > we're fixing them.
> > 
> > > 
> > > > So add a VIRTUAL_BUG_ON() to trap all non-linear and non-symbol
> > > > addresses (e.g., stack addresses)
> > > > 
> > > > Tested by pass stack addresses and symbol addresses to __pa(). Result:
> > > > stack addresses: kernel BUG()
> > > 
> > > Either:
> > > 
> > > * Stacks are vmap'd, and __is_lm_address(stack_addr) is false. We'll
> > >   produce a WARNING() today (and return a junk physical address).
> > > 
> > > * Stacks are linear mapped, and cannot be distinguished from other
> > >   linear mapped addresses. The physical address will be valid.
> > > 
> > > ... so I don't understand why you need to change this.
> > 
> > For the first case: for vmap'd stack, __pa() returns a junk
> > physical address and it might be easier to debug this incorrect address
> > translation by a BUG() call instead of monitoring the warning log.
> 
> I think that's an argument for upgrading the existing WARN() to a BUG(),
> rather than adding a separate VIRTUAL_BUG_ON().
> 
> However, there are cases where the junk physical address is not used to
> perform an access, and the WARN() is more helpful.

got it.

> 
> You can set panic_on_warn to get an immediate panic() when the WARN()
> fires. Is there some reason that approach doesn't work for you?

panic_on_warn works fine. thanks for your comment.


cheers,
Miles

> 
> Thanks,
> Mark.



_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel