Re: [Xen-devel] [PATCH 5/7] xen/arm: traps: Avoid BUG_ON() in do_trap_brk()

[Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>]

Julien Grall writes:

> At the moment, do_trap_brk() is using a BUG_ON() to check the hardware
> has been correctly configured during boot.
>
> Any error when configuring the hardware could result to a guest 'brk'
> trapping in the hypervisor and crash it.
>
> This is pretty harsh to kill Xen when actually killing the guest would
> be enough as misconfiguring this trap would not lead to exposing
> sensitive data. Replace the BUG_ON() with crashing the guest.
>
> Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>

> ---
>  xen/arch/arm/traps.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 132686ee0f..ef37ca6bde 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1304,10 +1304,15 @@ int do_bug_frame(const struct cpu_user_regs *regs, vaddr_t pc)
>  #ifdef CONFIG_ARM_64
>  static void do_trap_brk(struct cpu_user_regs *regs, const union hsr hsr)
>  {
> -    /* HCR_EL2.TGE and MDCR_EL2.TDE are not set so we never receive
> -     * software breakpoint exception for EL1 and EL0 here.
> +    /*
> +     * HCR_EL2.TGE and MDCR_EL2.TDR are currently not set. So we should
> +     * never receive software breakpoing exception for EL1 and EL0 here.
>       */
> -    BUG_ON(!hyp_mode(regs));
> +    if ( !hyp_mode(regs) )
> +    {
> +        domain_crash(current->domain);
> +        return;
> +    }
>  
>      switch ( hsr.brk.comment )
>      {


-- 
Volodymyr Babchuk at EPAM
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