diff mbox series

[v3] KVM: x86/xen: add support for 32-bit guests in SCHEDOP_poll

Message ID 1fd9826b2319cc9e58aecf6e11348acd63fdb81c.camel@infradead.org (mailing list archive)
State New, archived
Headers show
Series [v3] KVM: x86/xen: add support for 32-bit guests in SCHEDOP_poll | expand

Commit Message

David Woodhouse Nov. 25, 2022, 3 p.m. UTC 
From: Metin Kaya <metikaya@amazon.com>

This patch introduces compat version of struct sched_poll for
SCHEDOP_poll sub-operation of sched_op hypercall, reads correct amount
of data (16 bytes in 32-bit case, 24 bytes otherwise) by using new
compat_sched_poll struct, copies it to sched_poll properly, and lets
rest of the code run as is.

Signed-off-by: Metin Kaya <metikaya@amazon.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
v2 (Metin): Updated a comment and added a new one.
v3 (dwmw2): Take the simple path on 32-bit host, minor cosmetics.

I would have liked a self-test, but that requires actually invoking the
hypercall from 32-bit mode and AFAICT the KVM self-tests don't support
that, so it's probably not reasonable to demand that Metin implement it
just to test this relatively simple case.

 arch/x86/kvm/xen.c | 33 +++++++++++++++++++++++++++++----
 arch/x86/kvm/xen.h |  7 +++++++
 2 files changed, 36 insertions(+), 4 deletions(-)

Comments

Paul Durrant Nov. 30, 2022, 2:22 p.m. UTC | #1 
On 25/11/2022 15:00, David Woodhouse wrote:
> From: Metin Kaya <metikaya@amazon.com>
> 
> This patch introduces compat version of struct sched_poll for
> SCHEDOP_poll sub-operation of sched_op hypercall, reads correct amount
> of data (16 bytes in 32-bit case, 24 bytes otherwise) by using new
> compat_sched_poll struct, copies it to sched_poll properly, and lets
> rest of the code run as is.
> 
> Signed-off-by: Metin Kaya <metikaya@amazon.com>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

Reviewed-by: Paul Durrant <paul@xen.org>
diff mbox series

Patch

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index c3180fe9d918..f1f6d849ed50 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1157,20 +1157,45 @@  static bool kvm_xen_schedop_poll(struct kvm_vcpu *vcpu, bool longmode,
 	evtchn_port_t port, *ports;
 	gpa_t gpa;
 
-	if (!longmode || !lapic_in_kernel(vcpu) ||
+	if (!lapic_in_kernel(vcpu) ||
 	    !(vcpu->kvm->arch.xen_hvm_config.flags & KVM_XEN_HVM_CONFIG_EVTCHN_SEND))
 		return false;
 
 	idx = srcu_read_lock(&vcpu->kvm->srcu);
 	gpa = kvm_mmu_gva_to_gpa_system(vcpu, param, NULL);
 	srcu_read_unlock(&vcpu->kvm->srcu, idx);
-
-	if (!gpa || kvm_vcpu_read_guest(vcpu, gpa, &sched_poll,
-					sizeof(sched_poll))) {
+	if (!gpa) {
 		*r = -EFAULT;
 		return true;
 	}
 
+	if (IS_ENABLED(CONFIG_64BIT) && !longmode) {
+		struct compat_sched_poll sp32;
+
+		/* Sanity check that the compat struct definition is correct */
+		BUILD_BUG_ON(sizeof(sp32) != 16);
+
+		if (kvm_vcpu_read_guest(vcpu, gpa, &sp32, sizeof(sp32))) {
+			*r = -EFAULT;
+			return true;
+		}
+
+		/*
+		 * This is a 32-bit pointer to an array of evtchn_port_t which
+		 * are uint32_t, so once it's converted no further compat
+		 * handling is needed.
+		 */
+		sched_poll.ports = (void *)(unsigned long)(sp32.ports);
+		sched_poll.nr_ports = sp32.nr_ports;
+		sched_poll.timeout = sp32.timeout;
+	} else {
+		if (kvm_vcpu_read_guest(vcpu, gpa, &sched_poll,
+					sizeof(sched_poll))) {
+			*r = -EFAULT;
+			return true;
+		}
+	}
+
 	if (unlikely(sched_poll.nr_ports > 1)) {
 		/* Xen (unofficially) limits number of pollers to 128 */
 		if (sched_poll.nr_ports > 128) {
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index 8503d2c6891e..ea33d80a0c51 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -207,4 +207,11 @@  struct compat_vcpu_runstate_info {
     uint64_t time[4];
 } __attribute__((packed));
 
+struct compat_sched_poll {
+	/* This is actually a guest virtual address which points to ports. */
+	uint32_t ports;
+	unsigned int nr_ports;
+	uint64_t timeout;
+};
+
 #endif /* __ARCH_X86_KVM_XEN_H__ */