On Wed, Mar 19, 2025 at 09:15:54AM +0000, Marc Zyngier wrote:
On Wed, 19 Mar 2025 00:26:14 +0000, Gavin Shan gshan@redhat.com wrote:
On 3/14/25 10:35 AM, Mark Brown wrote:
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c index 4e757a77322c9efc59cdff501745f7c80d452358..1c8e2ad32e8c396fc4b11d5fec2e86728f2829d9 100644 --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c @@ -5,6 +5,7 @@ */ #include <hyp/adjust_pc.h> +#include <hyp/switch.h> #include <asm/pgtable-types.h> #include <asm/kvm_asm.h> @@ -176,8 +177,12 @@ static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt) sync_hyp_vcpu(hyp_vcpu); pkvm_put_hyp_vcpu(hyp_vcpu); } else {
struct kvm_vcpu *vcpu = kern_hyp_va(host_vcpu);- /* The host is fully trusted, run its vCPU directly. */
ret = __kvm_vcpu_run(host_vcpu);
fpsimd_lazy_switch_to_guest(vcpu);ret = __kvm_vcpu_run(vcpu);fpsimd_lazy_switch_to_host(vcpu);@host_vcpu should have been hypervisor's linear mapping address in v6.12. It looks incorrect to assume it's a kernel's linear mapping address and convert it (@host_vcpu) to the hypervisor's linear address agin, if I don't miss anything.
host_vcpu is passed as a parameter to the hypercall, and is definitely a kernel address.
However, at this stage, we have *already* converted it to a HYP VA:
https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/ar...
That's also the case in v6.13; the earlier conversion was removed in v6.14-rc1 in commit:
f7d03fcbf1f48206 ("KVM: arm64: Introduce __pkvm_vcpu_{load,put}()")
... where the code in the 'else' block changed from:
| ret = __kvm_vcpu_run(host_vcpu);
... to:
ret = __kvm_vcpu_run(kern_hyp_va(host_vcpu)); |
In the upstream version of this patch, the code here changed from
| /* The host is fully trusted, run its vCPU directly. */ | ret = __kvm_vcpu_run(kern_hyp_va(host_vcpu));
... to:
| struct kvm_vcpu *vcpu = kern_hyp_va(host_vcpu); | | /* The host is fully trusted, run its vCPU directly. */ | fpsimd_lazy_switch_to_guest(vcpu); | ret = __kvm_vcpu_run(vcpu); | fpsimd_lazy_switch_to_host(vcpu);
The result is that this change is turning a perfectly valid HYP VA into... something. Odds are that the masking/patching will not mess up the address, but this is completely buggy anyway. In general, kern_hyp_va() is not an idempotent operation.
IIUC today it *happens* to be idempotent, but as you say that is not guaranteed to remain the case, and this is definitely a logical bug.
Thanks for noticing that something was wrong.
Broonie, can you please look into this?
Greg, it may be more prudent to unstage this series from 6.12-stable until we know for sure this is the only problem.
As above, likewise with the v6.13 version.
I'll go reply there linking to this thread.
Mark.