[PATCH] xen/arm: traps: Don't panic when receiving an unknown debug trap

[PATCH] xen/arm: traps: Don't panic when receiving an unknown debug trap

[Julien Grall]

From: Julien Grall <jgrall@amazon.com>

Even if debug trap are only meant for debugging purpose, it is quite
harsh to crash Xen if one of the trap sent by the guest is not handled.

So switch from a panic() to a printk().

Signed-off-by: Julien Grall <jgrall@amazon.com>
---
 xen/arch/arm/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 8f40d0e0b6b1..a36f145e6739 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1410,7 +1410,7 @@ static void do_debug_trap(struct cpu_user_regs *regs, unsigned int code)
         show_execution_state(regs);
         break;
     default:
-        panic("DOM%d: Unhandled debug trap %#x\n", domid, code);
+        printk("DOM%d: Unhandled debug trap %#x\n", domid, code);
         break;
     }
 }
-- 
2.17.1

Re: [PATCH] xen/arm: traps: Don't panic when receiving an unknown debug trap

[Elliott Mitchell]

On Thu, Nov 05, 2020 at 10:31:06PM +0000, Julien Grall wrote:
> Even if debug trap are only meant for debugging purpose, it is quite
> harsh to crash Xen if one of the trap sent by the guest is not handled.
> 
> So switch from a panic() to a printk().

Might this qualify as security due to potential DoS?


-- 
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Re: [PATCH] xen/arm: traps: Don't panic when receiving an unknown debug trap

[Julien Grall]

On 05/11/2020 23:10, Elliott Mitchell wrote:
> On Thu, Nov 05, 2020 at 10:31:06PM +0000, Julien Grall wrote:
>> Even if debug trap are only meant for debugging purpose, it is quite
>> harsh to crash Xen if one of the trap sent by the guest is not handled.
>>
>> So switch from a panic() to a printk().
> 
> Might this qualify as security due to potential DoS?
This code path only exists with CONFIG_DEBUG=y which is not security 
supported.

Cheers,

-- 
Julien Grall

Re: [PATCH] xen/arm: traps: Don't panic when receiving an unknown debug trap

[Stefano Stabellini]

On Thu, 5 Nov 2020, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
> 
> Even if debug trap are only meant for debugging purpose, it is quite
> harsh to crash Xen if one of the trap sent by the guest is not handled.
> 
> So switch from a panic() to a printk().
> 
> Signed-off-by: Julien Grall <jgrall@amazon.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

> ---
>  xen/arch/arm/traps.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 8f40d0e0b6b1..a36f145e6739 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1410,7 +1410,7 @@ static void do_debug_trap(struct cpu_user_regs *regs, unsigned int code)
>          show_execution_state(regs);
>          break;
>      default:
> -        panic("DOM%d: Unhandled debug trap %#x\n", domid, code);
> +        printk("DOM%d: Unhandled debug trap %#x\n", domid, code);
>          break;
>      }
>  }
> -- 
> 2.17.1
> 

Re: [PATCH] xen/arm: traps: Don't panic when receiving an unknown debug trap

[Bertrand Marquis]

Hi Julien,

> On 5 Nov 2020, at 22:31, Julien Grall <julien@xen.org> wrote:
> 
> From: Julien Grall <jgrall@amazon.com>
> 
> Even if debug trap are only meant for debugging purpose, it is quite
> harsh to crash Xen if one of the trap sent by the guest is not handled.
> 
> So switch from a panic() to a printk().

Very smart idea :-)

> 
> Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

Cheers
Bertrand

> ---
> xen/arch/arm/traps.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 8f40d0e0b6b1..a36f145e6739 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1410,7 +1410,7 @@ static void do_debug_trap(struct cpu_user_regs *regs, unsigned int code)
>         show_execution_state(regs);
>         break;
>     default:
> -        panic("DOM%d: Unhandled debug trap %#x\n", domid, code);
> +        printk("DOM%d: Unhandled debug trap %#x\n", domid, code);
>         break;
>     }
> }
> -- 
> 2.17.1
> 
>