| Message ID | 20181017182116.22603-1-christoffer.dall@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: Safety check PSTATE when entering guest and handle IL | expand |
On 17 October 2018 at 19:21, Christoffer Dall <christoffer.dall@arm.com> wrote: > This commit adds a paranoid check when entering the guest to make sure > we don't attempt running guest code in an equally or more privilged mode > than the hypervisor. We also catch other accidental programming of the > SPSR_EL2 which results in an illegal exception return and report this > safely back to the user. > > Signed-off-by: Christoffer Dall <christoffer.dall@arm.com> > --- > diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c > index 9ce223944983..d7ac15412c97 100644 > --- a/arch/arm64/kvm/hyp/sysreg-sr.c > +++ b/arch/arm64/kvm/hyp/sysreg-sr.c > @@ -152,8 +152,25 @@ static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt) > static void __hyp_text > __sysreg_restore_el2_return_state(struct kvm_cpu_context *ctxt) > { > + u64 pstate = ctxt->gp_regs.regs.pstate; > + u64 mode = pstate & PSR_AA32_MODE_MASK; > + > + /* > + * Safety check to ensure we're setting the CPU up to enter the guest > + * in a less privileged mode. > + * > + * If we are attempting a return to EL2 or higher in AArch64 state, > + * program SPSR_EL2 with M=EL2h and the IL bit set which ensures that > + * we'll take an illegal exception return exception immediately after This should read "illegal exception state exception", I think (for the 64-bit case we don't do an illegal exception return, we do a legal exception return that sets PSTATE.IL to 1.) > + * the ERET to the guest. Attempts to return to AArch32 Hyp will > + * result in an illegal exception return because EL2's execution state > + * is determined by SCR_EL3.RW. > + */ > + if (!(mode & PSR_MODE32_BIT) && mode >= PSR_MODE_EL2t) > + pstate = PSR_MODE_EL2h | PSR_IL_BIT; thanks -- PMM
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h index 102b5a5c47b6..7738b4882d18 100644 --- a/arch/arm64/include/asm/kvm_asm.h +++ b/arch/arm64/include/asm/kvm_asm.h @@ -30,6 +30,7 @@ #define ARM_EXCEPTION_IRQ 0 #define ARM_EXCEPTION_EL1_SERROR 1 #define ARM_EXCEPTION_TRAP 2 +#define ARM_EXCEPTION_IL 3 /* The hyp-stub will return this for any kvm_call_hyp() call */ #define ARM_EXCEPTION_HYP_GONE HVC_STUB_ERR diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h index 177b851ca6d9..ff35ac1258eb 100644 --- a/arch/arm64/include/asm/ptrace.h +++ b/arch/arm64/include/asm/ptrace.h @@ -25,6 +25,9 @@ #define CurrentEL_EL1 (1 << 2) #define CurrentEL_EL2 (2 << 2) +/* Additional SPSR bits not exposed in the UABI */ +#define PSR_IL_BIT (1 << 20) + /* AArch32-specific ptrace requests */ #define COMPAT_PTRACE_GETREGS 12 #define COMPAT_PTRACE_SETREGS 13 diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c index e5e741bfffe1..35a81bebd02b 100644 --- a/arch/arm64/kvm/handle_exit.c +++ b/arch/arm64/kvm/handle_exit.c @@ -284,6 +284,13 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run, */ run->exit_reason = KVM_EXIT_FAIL_ENTRY; return 0; + case ARM_EXCEPTION_IL: + /* + * We attempted an illegal exception return. Guest state must + * have been corrupted somehow. Give up. + */ + run->exit_reason = KVM_EXIT_FAIL_ENTRY; + return -EINVAL; default: kvm_pr_unimpl("Unsupported exception type: %d", exception_index); diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S index 24b4fbafe3e4..b1f14f736962 100644 --- a/arch/arm64/kvm/hyp/hyp-entry.S +++ b/arch/arm64/kvm/hyp/hyp-entry.S @@ -162,6 +162,20 @@ el1_error: mov x0, #ARM_EXCEPTION_EL1_SERROR b __guest_exit +el2_sync: + /* Check for illegal exception return, otherwise panic */ + mrs x0, spsr_el2 + + /* if this was something else, then panic! */ + tst x0, #PSR_IL_BIT + b.eq __hyp_panic + + /* Let's attempt a recovery from the illegal exception return */ + get_vcpu_ptr x1, x0 + mov x0, #ARM_EXCEPTION_IL + b __guest_exit + + el2_error: ldp x0, x1, [sp], #16 @@ -240,7 +254,7 @@ ENTRY(__kvm_hyp_vector) invalid_vect el2t_fiq_invalid // FIQ EL2t invalid_vect el2t_error_invalid // Error EL2t - invalid_vect el2h_sync_invalid // Synchronous EL2h + valid_vect el2_sync // Synchronous EL2h invalid_vect el2h_irq_invalid // IRQ EL2h invalid_vect el2h_fiq_invalid // FIQ EL2h valid_vect el2_error // Error EL2h diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c index 9ce223944983..d7ac15412c97 100644 --- a/arch/arm64/kvm/hyp/sysreg-sr.c +++ b/arch/arm64/kvm/hyp/sysreg-sr.c @@ -152,8 +152,25 @@ static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt) static void __hyp_text __sysreg_restore_el2_return_state(struct kvm_cpu_context *ctxt) { + u64 pstate = ctxt->gp_regs.regs.pstate; + u64 mode = pstate & PSR_AA32_MODE_MASK; + + /* + * Safety check to ensure we're setting the CPU up to enter the guest + * in a less privileged mode. + * + * If we are attempting a return to EL2 or higher in AArch64 state, + * program SPSR_EL2 with M=EL2h and the IL bit set which ensures that + * we'll take an illegal exception return exception immediately after + * the ERET to the guest. Attempts to return to AArch32 Hyp will + * result in an illegal exception return because EL2's execution state + * is determined by SCR_EL3.RW. + */ + if (!(mode & PSR_MODE32_BIT) && mode >= PSR_MODE_EL2t) + pstate = PSR_MODE_EL2h | PSR_IL_BIT; + write_sysreg_el2(ctxt->gp_regs.regs.pc, elr); - write_sysreg_el2(ctxt->gp_regs.regs.pstate, spsr); + write_sysreg_el2(pstate, spsr); if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN)) write_sysreg_s(ctxt->sys_regs[DISR_EL1], SYS_VDISR_EL2);
This commit adds a paranoid check when entering the guest to make sure we don't attempt running guest code in an equally or more privilged mode than the hypervisor. We also catch other accidental programming of the SPSR_EL2 which results in an illegal exception return and report this safely back to the user. Signed-off-by: Christoffer Dall <christoffer.dall@arm.com> --- arch/arm64/include/asm/kvm_asm.h | 1 + arch/arm64/include/asm/ptrace.h | 3 +++ arch/arm64/kvm/handle_exit.c | 7 +++++++ arch/arm64/kvm/hyp/hyp-entry.S | 16 +++++++++++++++- arch/arm64/kvm/hyp/sysreg-sr.c | 19 ++++++++++++++++++- 5 files changed, 44 insertions(+), 2 deletions(-)