Re: [Xen-devel] [PATCH for-4.12] x86/svm: Fix handling of ICEBP intercepts

["Woods, Brian" <Brian.Woods@xxxxxxx>]

On 2/1/19 8:49 AM, Andrew Cooper wrote:
> c/s 9338a37d "x86/svm: implement debug events" added support for introspecting
> ICEBP debug exceptions, but didn't account for the fact that
> svm_get_insn_len() (previously __get_instruction_length) can fail and may
> already raise #GP for the guest.
> 
> If svm_get_insn_len() fails, return back to guest context rather than
> continuing and mistaking a trap-style VMExit for a fault-style one.
> 
> Spotted by Coverity.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> CC: Brian Woods <brian.woods@xxxxxxx>
> CC: Juergen Gross <jgross@xxxxxxxx>
> CC: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> CC: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> 
> This wants backporting to Xen 4.11
> ---
>   xen/arch/x86/hvm/svm/svm.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> index 2584b90..e21091c 100644
> --- a/xen/arch/x86/hvm/svm/svm.c
> +++ b/xen/arch/x86/hvm/svm/svm.c
> @@ -2758,6 +2758,9 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
>               {
>                   trap_type = X86_EVENTTYPE_PRI_SW_EXCEPTION;
>                   inst_len = svm_get_insn_len(v, INSTR_ICEBP);
> +
> +                if ( !instr_len )
> +                    break;
>               }
>   
>               rc = hvm_monitor_debug(regs->rip,
> 

Acked-by: Brian Woods <brian.woods@xxxxxxx>
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