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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The discovery of further cascade errors doesn't change the need for this
patch.

Its obviously missed the boat for 4.12, but still needed.

I haven't reposed with the typo which Tamas fixed, but will fold that in
on commit.  (I didn't think it worthy of sending out a v2, given the
obviousness of the fix.)

~Andrew

On 01/02/2019 14:49, 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,


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