Merge tag 'kvm-x86-generic-6.12' of https://github.com/kvm-x86/linux into HEAD

KVK generic changes for 6.12:

 - Fix a bug that results in KVM prematurely exiting to userspace for coalesced
   MMIO/PIO in many cases, clean up the related code, and add a testcase.

 - Fix a bug in kvm_clear_guest() where it would trigger a buffer overflow _if_
   the gpa+len crosses a page boundary, which thankfully is guaranteed to not
   happen in the current code base.  Add WARNs in more helpers that read/write
   guest memory to detect similar bugs.

tools/testing/selftests/kvm/Makefile

@@ -130,6 +130,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/max_vcpuid_cap_test
 TEST_GEN_PROGS_x86_64 += x86_64/triple_fault_event_test
 TEST_GEN_PROGS_x86_64 += x86_64/recalc_apic_map_test
 TEST_GEN_PROGS_x86_64 += access_tracking_perf_test
+TEST_GEN_PROGS_x86_64 += coalesced_io_test
 TEST_GEN_PROGS_x86_64 += demand_paging_test
 TEST_GEN_PROGS_x86_64 += dirty_log_test
 TEST_GEN_PROGS_x86_64 += dirty_log_perf_test
@@ -167,6 +168,7 @@ TEST_GEN_PROGS_aarch64 += aarch64/vpmu_counter_access
 TEST_GEN_PROGS_aarch64 += aarch64/no-vgic-v3
 TEST_GEN_PROGS_aarch64 += access_tracking_perf_test
 TEST_GEN_PROGS_aarch64 += arch_timer
+TEST_GEN_PROGS_aarch64 += coalesced_io_test
 TEST_GEN_PROGS_aarch64 += demand_paging_test
 TEST_GEN_PROGS_aarch64 += dirty_log_test
 TEST_GEN_PROGS_aarch64 += dirty_log_perf_test
@@ -201,6 +203,7 @@ TEST_GEN_PROGS_s390x += kvm_binary_stats_test
 TEST_GEN_PROGS_riscv += riscv/sbi_pmu_test
 TEST_GEN_PROGS_riscv += riscv/ebreak_test
 TEST_GEN_PROGS_riscv += arch_timer
+TEST_GEN_PROGS_riscv += coalesced_io_test
 TEST_GEN_PROGS_riscv += demand_paging_test
 TEST_GEN_PROGS_riscv += dirty_log_test
 TEST_GEN_PROGS_riscv += get-reg-list

tools/testing/selftests/kvm/coalesced_io_test.c

@@ -0,0 +1,236 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+#include <linux/sizes.h>
+
+#include <kvm_util.h>
+#include <processor.h>
+
+#include "ucall_common.h"
+
+struct kvm_coalesced_io {
+	struct kvm_coalesced_mmio_ring *ring;
+	uint32_t ring_size;
+	uint64_t mmio_gpa;
+	uint64_t *mmio;
+
+	/*
+	 * x86-only, but define pio_port for all architectures to minimize the
+	 * amount of #ifdeffery and complexity, without having to sacrifice
+	 * verbose error messages.
+	 */
+	uint8_t pio_port;
+};
+
+static struct kvm_coalesced_io kvm_builtin_io_ring;
+
+#ifdef __x86_64__
+static const int has_pio = 1;
+#else
+static const int has_pio = 0;
+#endif
+
+static void guest_code(struct kvm_coalesced_io *io)
+{
+	int i, j;
+
+	for (;;) {
+		for (j = 0; j < 1 + has_pio; j++) {
+			/*
+			 * KVM always leaves one free entry, i.e. exits to
+			 * userspace before the last entry is filled.
+			 */
+			for (i = 0; i < io->ring_size - 1; i++) {
+#ifdef __x86_64__
+				if (i & 1)
+					outl(io->pio_port, io->pio_port + i);
+				else
+#endif
+					WRITE_ONCE(*io->mmio, io->mmio_gpa + i);
+			}
+#ifdef __x86_64__
+			if (j & 1)
+				outl(io->pio_port, io->pio_port + i);
+			else
+#endif
+				WRITE_ONCE(*io->mmio, io->mmio_gpa + i);
+		}
+		GUEST_SYNC(0);
+
+		WRITE_ONCE(*io->mmio, io->mmio_gpa + i);
+#ifdef __x86_64__
+		outl(io->pio_port, io->pio_port + i);
+#endif
+	}
+}
+
+static void vcpu_run_and_verify_io_exit(struct kvm_vcpu *vcpu,
+					struct kvm_coalesced_io *io,
+					uint32_t ring_start,
+					uint32_t expected_exit)
+{
+	const bool want_pio = expected_exit == KVM_EXIT_IO;
+	struct kvm_coalesced_mmio_ring *ring = io->ring;
+	struct kvm_run *run = vcpu->run;
+	uint32_t pio_value;
+
+	WRITE_ONCE(ring->first, ring_start);
+	WRITE_ONCE(ring->last, ring_start);
+
+	vcpu_run(vcpu);
+
+	/*
+	 * Annoyingly, reading PIO data is safe only for PIO exits, otherwise
+	 * data_offset is garbage, e.g. an MMIO gpa.
+	 */
+	if (run->exit_reason == KVM_EXIT_IO)
+		pio_value = *(uint32_t *)((void *)run + run->io.data_offset);
+	else
+		pio_value = 0;
+
+	TEST_ASSERT((!want_pio && (run->exit_reason == KVM_EXIT_MMIO && run->mmio.is_write &&
+				   run->mmio.phys_addr == io->mmio_gpa && run->mmio.len == 8 &&
+				   *(uint64_t *)run->mmio.data == io->mmio_gpa + io->ring_size - 1)) ||
+		    (want_pio  && (run->exit_reason == KVM_EXIT_IO && run->io.port == io->pio_port &&
+				   run->io.direction == KVM_EXIT_IO_OUT && run->io.count == 1 &&
+				   pio_value == io->pio_port + io->ring_size - 1)),
+		    "For start = %u, expected exit on %u-byte %s write 0x%llx = %lx, got exit_reason = %u (%s)\n  "
+		    "(MMIO addr = 0x%llx, write = %u, len = %u, data = %lx)\n  "
+		    "(PIO port = 0x%x, write = %u, len = %u, count = %u, data = %x",
+		    ring_start, want_pio ? 4 : 8, want_pio ? "PIO" : "MMIO",
+		    want_pio ? (unsigned long long)io->pio_port : io->mmio_gpa,
+		    (want_pio ? io->pio_port : io->mmio_gpa) + io->ring_size - 1, run->exit_reason,
+		    run->exit_reason == KVM_EXIT_MMIO ? "MMIO" : run->exit_reason == KVM_EXIT_IO ? "PIO" : "other",
+		    run->mmio.phys_addr, run->mmio.is_write, run->mmio.len, *(uint64_t *)run->mmio.data,
+		    run->io.port, run->io.direction, run->io.size, run->io.count, pio_value);
+}
+
+static void vcpu_run_and_verify_coalesced_io(struct kvm_vcpu *vcpu,
+					     struct kvm_coalesced_io *io,
+					     uint32_t ring_start,
+					     uint32_t expected_exit)
+{
+	struct kvm_coalesced_mmio_ring *ring = io->ring;
+	int i;
+
+	vcpu_run_and_verify_io_exit(vcpu, io, ring_start, expected_exit);
+
+	TEST_ASSERT((ring->last + 1) % io->ring_size == ring->first,
+		    "Expected ring to be full (minus 1), first = %u, last = %u, max = %u, start = %u",
+		    ring->first, ring->last, io->ring_size, ring_start);
+
+	for (i = 0; i < io->ring_size - 1; i++) {
+		uint32_t idx = (ring->first + i) % io->ring_size;
+		struct kvm_coalesced_mmio *entry = &ring->coalesced_mmio[idx];
+
+#ifdef __x86_64__
+		if (i & 1)
+			TEST_ASSERT(entry->phys_addr == io->pio_port &&
+				    entry->len == 4 && entry->pio &&
+				    *(uint32_t *)entry->data == io->pio_port + i,
+				    "Wanted 4-byte port I/O 0x%x = 0x%x in entry %u, got %u-byte %s 0x%llx = 0x%x",
+				    io->pio_port, io->pio_port + i, i,
+				    entry->len, entry->pio ? "PIO" : "MMIO",
+				    entry->phys_addr, *(uint32_t *)entry->data);
+		else
+#endif
+			TEST_ASSERT(entry->phys_addr == io->mmio_gpa &&
+				    entry->len == 8 && !entry->pio,
+				    "Wanted 8-byte MMIO to 0x%lx = %lx in entry %u, got %u-byte %s 0x%llx = 0x%lx",
+				    io->mmio_gpa, io->mmio_gpa + i, i,
+				    entry->len, entry->pio ? "PIO" : "MMIO",
+				    entry->phys_addr, *(uint64_t *)entry->data);
+	}
+}
+
+static void test_coalesced_io(struct kvm_vcpu *vcpu,
+			      struct kvm_coalesced_io *io, uint32_t ring_start)
+{
+	struct kvm_coalesced_mmio_ring *ring = io->ring;
+
+	kvm_vm_register_coalesced_io(vcpu->vm, io->mmio_gpa, 8, false /* pio */);
+#ifdef __x86_64__
+	kvm_vm_register_coalesced_io(vcpu->vm, io->pio_port, 8, true /* pio */);
+#endif
+
+	vcpu_run_and_verify_coalesced_io(vcpu, io, ring_start, KVM_EXIT_MMIO);
+#ifdef __x86_64__
+	vcpu_run_and_verify_coalesced_io(vcpu, io, ring_start, KVM_EXIT_IO);
+#endif
+
+	/*
+	 * Verify ucall, which may use non-coalesced MMIO or PIO, generates an
+	 * immediate exit.
+	 */
+	WRITE_ONCE(ring->first, ring_start);
+	WRITE_ONCE(ring->last, ring_start);
+	vcpu_run(vcpu);
+	TEST_ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_SYNC);
+	TEST_ASSERT_EQ(ring->first, ring_start);
+	TEST_ASSERT_EQ(ring->last, ring_start);
+
+	/* Verify that non-coalesced MMIO/PIO generates an exit to userspace. */
+	kvm_vm_unregister_coalesced_io(vcpu->vm, io->mmio_gpa, 8, false /* pio */);
+	vcpu_run_and_verify_io_exit(vcpu, io, ring_start, KVM_EXIT_MMIO);
+
+#ifdef __x86_64__
+	kvm_vm_unregister_coalesced_io(vcpu->vm, io->pio_port, 8, true /* pio */);
+	vcpu_run_and_verify_io_exit(vcpu, io, ring_start, KVM_EXIT_IO);
+#endif
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	int i;
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_COALESCED_MMIO));
+
+#ifdef __x86_64__
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_COALESCED_PIO));
+#endif
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+
+	kvm_builtin_io_ring = (struct kvm_coalesced_io) {
+		/*
+		 * The I/O ring is a kernel-allocated page whose address is
+		 * relative to each vCPU's run page, with the page offset
+		 * provided by KVM in the return of KVM_CAP_COALESCED_MMIO.
+		 */
+		.ring = (void *)vcpu->run +
+			(kvm_check_cap(KVM_CAP_COALESCED_MMIO) * getpagesize()),
+
+		/*
+		 * The size of the I/O ring is fixed, but KVM defines the sized
+		 * based on the kernel's PAGE_SIZE.  Thus, userspace must query
+		 * the host's page size at runtime to compute the ring size.
+		 */
+		.ring_size = (getpagesize() - sizeof(struct kvm_coalesced_mmio_ring)) /
+			     sizeof(struct kvm_coalesced_mmio),
+
+		/*
+		 * Arbitrary address+port (MMIO mustn't overlap memslots), with
+		 * the MMIO GPA identity mapped in the guest.
+		 */
+		.mmio_gpa = 4ull * SZ_1G,
+		.mmio = (uint64_t *)(4ull * SZ_1G),
+		.pio_port = 0x80,
+	};
+
+	virt_map(vm, (uint64_t)kvm_builtin_io_ring.mmio, kvm_builtin_io_ring.mmio_gpa, 1);
+
+	sync_global_to_guest(vm, kvm_builtin_io_ring);
+	vcpu_args_set(vcpu, 1, &kvm_builtin_io_ring);
+
+	for (i = 0; i < kvm_builtin_io_ring.ring_size; i++)
+		test_coalesced_io(vcpu, &kvm_builtin_io_ring, i);
+
+	kvm_vm_free(vm);
+	return 0;
+}

tools/testing/selftests/kvm/include/kvm_util.h

@@ -460,6 +460,32 @@ static inline uint32_t kvm_vm_reset_dirty_ring(struct kvm_vm *vm)
 	return __vm_ioctl(vm, KVM_RESET_DIRTY_RINGS, NULL);
 }
 
+static inline void kvm_vm_register_coalesced_io(struct kvm_vm *vm,
+						uint64_t address,
+						uint64_t size, bool pio)
+{
+	struct kvm_coalesced_mmio_zone zone = {
+		.addr = address,
+		.size = size,
+		.pio  = pio,
+	};
+
+	vm_ioctl(vm, KVM_REGISTER_COALESCED_MMIO, &zone);
+}
+
+static inline void kvm_vm_unregister_coalesced_io(struct kvm_vm *vm,
+						  uint64_t address,
+						  uint64_t size, bool pio)
+{
+	struct kvm_coalesced_mmio_zone zone = {
+		.addr = address,
+		.size = size,
+		.pio  = pio,
+	};
+
+	vm_ioctl(vm, KVM_UNREGISTER_COALESCED_MMIO, &zone);
+}
+
 static inline int vm_get_stats_fd(struct kvm_vm *vm)
 {
 	int fd = __vm_ioctl(vm, KVM_GET_STATS_FD, NULL);

virt/kvm/coalesced_mmio.c

@@ -40,27 +40,6 @@ static int coalesced_mmio_in_range(struct kvm_coalesced_mmio_dev *dev,
 	return 1;
 }
 
-static int coalesced_mmio_has_room(struct kvm_coalesced_mmio_dev *dev, u32 last)
-{
-	struct kvm_coalesced_mmio_ring *ring;
-	unsigned avail;
-
-	/* Are we able to batch it ? */
-
-	/* last is the first free entry
-	 * check if we don't meet the first used entry
-	 * there is always one unused entry in the buffer
-	 */
-	ring = dev->kvm->coalesced_mmio_ring;
-	avail = (ring->first - last - 1) % KVM_COALESCED_MMIO_MAX;
-	if (avail == 0) {
-		/* full */
-		return 0;
-	}
-
-	return 1;
-}
-
 static int coalesced_mmio_write(struct kvm_vcpu *vcpu,
 				struct kvm_io_device *this, gpa_t addr,
 				int len, const void *val)
@@ -74,9 +53,15 @@ static int coalesced_mmio_write(struct kvm_vcpu *vcpu,
 
 	spin_lock(&dev->kvm->ring_lock);
 
+	/*
+	 * last is the index of the entry to fill.  Verify userspace hasn't
+	 * set last to be out of range, and that there is room in the ring.
+	 * Leave one entry free in the ring so that userspace can differentiate
+	 * between an empty ring and a full ring.
+	 */
 	insert = READ_ONCE(ring->last);
-	if (!coalesced_mmio_has_room(dev, insert) ||
+	if (insert >= KVM_COALESCED_MMIO_MAX ||
-	    insert >= KVM_COALESCED_MMIO_MAX) {
+	    (insert + 1) % KVM_COALESCED_MMIO_MAX == READ_ONCE(ring->first)) {
 		spin_unlock(&dev->kvm->ring_lock);
 		return -EOPNOTSUPP;
 	}

virt/kvm/kvm_main.c

@@ -3275,6 +3275,9 @@ static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
 	int r;
 	unsigned long addr;
 
+	if (WARN_ON_ONCE(offset + len > PAGE_SIZE))
+		return -EFAULT;
+
 	addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
 	if (kvm_is_error_hva(addr))
 		return -EFAULT;
@@ -3348,6 +3351,9 @@ static int __kvm_read_guest_atomic(struct kvm_memory_slot *slot, gfn_t gfn,
 	int r;
 	unsigned long addr;
 
+	if (WARN_ON_ONCE(offset + len > PAGE_SIZE))
+		return -EFAULT;
+
 	addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
 	if (kvm_is_error_hva(addr))
 		return -EFAULT;
@@ -3378,6 +3384,9 @@ static int __kvm_write_guest_page(struct kvm *kvm,
 	int r;
 	unsigned long addr;
 
+	if (WARN_ON_ONCE(offset + len > PAGE_SIZE))
+		return -EFAULT;
+
 	addr = gfn_to_hva_memslot(memslot, gfn);
 	if (kvm_is_error_hva(addr))
 		return -EFAULT;
@@ -3581,7 +3590,7 @@ int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len)
 	int ret;
 
 	while ((seg = next_segment(len, offset)) != 0) {
-		ret = kvm_write_guest_page(kvm, gfn, zero_page, offset, len);
+		ret = kvm_write_guest_page(kvm, gfn, zero_page, offset, seg);
 		if (ret < 0)
 			return ret;
 		offset = 0;