From: Mark Rutland <mark.rutland@xxxxxxx> If we panic in hyp mode, we inject a call to panic() into the EL1N host kernel. If a guest context is active, we first attempt to restore the minimal amount of state necessary to execute the host kernel with restore_sysregs. However, the SP is restored as part of restore_common_regs, and so we may return to the host's panic() function with the SP of the guest. Any calculations based on the SP will be bogus, and any attempt to access the stack will result in recursive data aborts. When running Linux as a guest, the guest's EL1N SP is like to be some valid kernel address. In this case, the host kernel may use that region as a stack for panic(), corrupting it in the process. Avoid the problem by restoring the host SP prior to returning to the host. To prevent misleading backtraces in the host, the FP is zeroed at the same time. We don't need any of the other "common" registers in order to panic successfully. Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx> Cc: <kvmarm@xxxxxxxxxxxxxxxxxxxxx> Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> --- arch/arm64/kvm/hyp.S | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S index e583613..1599701 100644 --- a/arch/arm64/kvm/hyp.S +++ b/arch/arm64/kvm/hyp.S @@ -880,6 +880,14 @@ __kvm_hyp_panic: bl __restore_sysregs + /* + * Make sure we have a valid host stack, and don't leave junk in the + * frame pointer that will give us a misleading host stack unwinding. + */ + ldr x22, [x2, #CPU_GP_REG_OFFSET(CPU_SP_EL1)] + msr sp_el1, x22 + mov x29, xzr + 1: adr x0, __hyp_panic_str adr x1, 2f ldp x2, x3, [x1] -- 2.1.2.330.g565301e.dirty -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
