On 10/21/20 14:51, Marc Zyngier wrote: > On 2020-10-21 14:35, Qais Yousef wrote: > > On 10/21/20 13:02, Marc Zyngier wrote: > > > On 2020-10-21 11:46, Qais Yousef wrote: > > > > On a system without uniform support for AArch32 at EL0, it is possible > > > > for the guest to force run AArch32 at EL0 and potentially cause an > > > > illegal exception if running on the wrong core. > > > > > > s/the wrong core/a core without AArch32/ > > > > > > > > > > > Add an extra check to catch if the guest ever does that and prevent it > > > > > > Not "if the guest ever does that". Rather "let's hope we are lucky > > > enough > > > to catch the guest doing that". > > > > > > > from running again by resetting vcpu->arch.target and return > > > > ARM_EXCEPTION_IL. > > > > > > > > We try to catch this misbehavior as early as possible and not rely on > > > > PSTATE.IL to occur. > > > > > > > > Tested on Juno by instrumenting the host to: > > > > > > > > * Fake asym aarch32. > > > > * Instrument KVM to make the asymmetry visible to the guest. > > > > > > > > Any attempt to run 32bit app in the guest will produce such error on > > > > qemu: > > > > > > Not *any* attempt. Only the ones where the guest exits whilst in > > > AArch32 EL0. It is perfectly possible for the guest to use AArch32 > > > undetected for quite a while. > > > > Thanks Marc! I'll change them all. > > > > > > > > > > # ./test > > > > error: kvm run failed Invalid argument > > > > PC=ffff800010945080 X00=ffff800016a45014 X01=ffff800010945058 > > > > X02=ffff800016917190 X03=0000000000000000 X04=0000000000000000 > > > > X05=00000000fffffffb X06=0000000000000000 X07=ffff80001000bab0 > > > > X08=0000000000000000 X09=0000000092ec5193 X10=0000000000000000 > > > > X11=ffff80001608ff40 X12=ffff000075fcde86 X13=ffff000075fcde88 > > > > X14=ffffffffffffffff X15=ffff00007b2105a8 X16=ffff00007b006d50 > > > > X17=0000000000000000 X18=0000000000000000 X19=ffff00007a82b000 > > > > X20=0000000000000000 X21=ffff800015ccd158 X22=ffff00007a82b040 > > > > X23=ffff00007a82b008 X24=0000000000000000 X25=ffff800015d169b0 > > > > X26=ffff8000126d05bc X27=0000000000000000 X28=0000000000000000 > > > > X29=ffff80001000ba90 X30=ffff80001093f3dc SP=ffff80001000ba90 > > > > PSTATE=60000005 -ZC- EL1h > > > > qemu-system-aarch64: Failed to get KVM_REG_ARM_TIMER_CNT > > > > > > It'd be worth working out: > > > - why does this show an AArch64 mode it we caught the vcpu in AArch32? > > > - why does QEMU shout about the timer register? > > > > /me puts a monocular on > > > > Which bit is the AArch64? > > It clearly spits out "EL1h", and PSTATE.M is 5, also consistent with EL1h. > > > It did surprise me that it is shouting about the timer. My guess was > > that > > a timer interrupt at the guest between exit/reentry caused the state > > change and > > the failure to read the timer register? Since the target is no longer > > valid it > > falls over, hopefully as expected. I could have been naive of course. > > That > > explanation made sense to my mind so I didn't dig further. > > Userspace is never involved with the timer interrupt, unless you've elected > to have the interrupt controller in userspace, which I seriously doubt. > > As we are introducing a change to the userspace ABI, it'd be interesting > to find out what is happening here. Sure. Let me educate myself more about this and find a way to interrogate qemu and KVM. Thanks -- Qais Yousef
