Add an x86 selftest to verify that KVM doesn't WARN or otherwise explode
if userspace modifies RCX during a userspace exit to handle string I/O.
This is a regression test for a user-triggerable WARN introduced by
commit 3b27de271839 ("KVM: x86: split the two parts of emulator_pio_in").
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
tools/testing/selftests/kvm/.gitignore | 1 +
tools/testing/selftests/kvm/Makefile | 1 +
.../selftests/kvm/x86_64/userspace_io_test.c | 114 ++++++++++++++++++
3 files changed, 116 insertions(+)
create mode 100644 tools/testing/selftests/kvm/x86_64/userspace_io_test.c
diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
index b8dbabe24ac2..691262c7b122 100644
--- a/tools/testing/selftests/kvm/.gitignore
+++ b/tools/testing/selftests/kvm/.gitignore
@@ -27,6 +27,7 @@
/x86_64/svm_int_ctl_test
/x86_64/sync_regs_test
/x86_64/tsc_msrs_test
+/x86_64/userspace_io_test
/x86_64/userspace_msr_exit_test
/x86_64/vmx_apic_access_test
/x86_64/vmx_close_while_nested_test
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index d1774f461393..1a611cb80c4e 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -58,6 +58,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/vmx_preemption_timer_test
TEST_GEN_PROGS_x86_64 += x86_64/svm_vmcall_test
TEST_GEN_PROGS_x86_64 += x86_64/svm_int_ctl_test
TEST_GEN_PROGS_x86_64 += x86_64/sync_regs_test
+TEST_GEN_PROGS_x86_64 += x86_64/userspace_io_test
TEST_GEN_PROGS_x86_64 += x86_64/userspace_msr_exit_test
TEST_GEN_PROGS_x86_64 += x86_64/vmx_apic_access_test
TEST_GEN_PROGS_x86_64 += x86_64/vmx_close_while_nested_test
diff --git a/tools/testing/selftests/kvm/x86_64/userspace_io_test.c b/tools/testing/selftests/kvm/x86_64/userspace_io_test.c
new file mode 100644
index 000000000000..e4bef2e05686
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/userspace_io_test.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+#include "test_util.h"
+
+#include "kvm_util.h"
+#include "processor.h"
+
+#define VCPU_ID 1
+
+static void guest_ins_port80(uint8_t *buffer, unsigned int count)
+{
+ unsigned long end;
+
+ if (count == 2)
+ end = (unsigned long)buffer + 1;
+ else
+ end = (unsigned long)buffer + 8192;
+
+ asm volatile("cld; rep; insb" : "+D"(buffer), "+c"(count) : "d"(0x80) : "memory");
+ GUEST_ASSERT_1(count == 0, count);
+ GUEST_ASSERT_2((unsigned long)buffer == end, buffer, end);
+}
+
+static void guest_code(void)
+{
+ uint8_t buffer[8192];
+ int i;
+
+ /*
+ * Special case tests. main() will adjust RCX 2 => 1 and 3 => 8192 to
+ * test that KVM doesn't explode when userspace modifies the "count" on
+ * a userspace I/O exit. KVM isn't required to play nice with the I/O
+ * itself as KVM doesn't support manipulating the count, it just needs
+ * to not explode or overflow a buffer.
+ */
+ guest_ins_port80(buffer, 2);
+ guest_ins_port80(buffer, 3);
+
+ /* Verify KVM fills the buffer correctly when not stuffing RCX. */
+ memset(buffer, 0, sizeof(buffer));
+ guest_ins_port80(buffer, 8192);
+ for (i = 0; i < 8192; i++)
+ GUEST_ASSERT_2(buffer[i] == 0xaa, i, buffer[i]);
+
+ GUEST_DONE();
+}
+
+int main(int argc, char *argv[])
+{
+ struct kvm_regs regs;
+ struct kvm_run *run;
+ struct kvm_vm *vm;
+ struct ucall uc;
+ int rc;
+
+ /* Tell stdout not to buffer its content */
+ setbuf(stdout, NULL);
+
+ /* Create VM */
+ vm = vm_create_default(VCPU_ID, 0, guest_code);
+ run = vcpu_state(vm, VCPU_ID);
+
+ memset(®s, 0, sizeof(regs));
+
+ while (1) {
+ rc = _vcpu_run(vm, VCPU_ID);
+
+ TEST_ASSERT(rc == 0, "vcpu_run failed: %d\n", rc);
+ TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+ "Unexpected exit reason: %u (%s),\n",
+ run->exit_reason,
+ exit_reason_str(run->exit_reason));
+
+ if (get_ucall(vm, VCPU_ID, &uc))
+ break;
+
+ TEST_ASSERT(run->io.port == 0x80,
+ "Expected I/O at port 0x80, got port 0x%x\n", run->io.port);
+
+ /*
+ * Modify the rep string count in RCX: 2 => 1 and 3 => 8192.
+ * Note, this abuses KVM's batching of rep string I/O to avoid
+ * getting stuck in an infinite loop. That behavior isn't in
+ * scope from a testing perspective as it's not ABI in any way,
+ * i.e. it really is abusing internal KVM knowledge.
+ */
+ vcpu_regs_get(vm, VCPU_ID, ®s);
+ if (regs.rcx == 2)
+ regs.rcx = 1;
+ if (regs.rcx == 3)
+ regs.rcx = 8192;
+ memset((void *)run + run->io.data_offset, 0xaa, 4096);
+ vcpu_regs_set(vm, VCPU_ID, ®s);
+ }
+
+ switch (uc.cmd) {
+ case UCALL_DONE:
+ break;
+ case UCALL_ABORT:
+ TEST_FAIL("%s at %s:%ld : argN+1 = 0x%lx, argN+2 = 0x%lx",
+ (const char *)uc.args[0], __FILE__, uc.args[1],
+ uc.args[2], uc.args[3]);
+ default:
+ TEST_FAIL("Unknown ucall %lu", uc.cmd);
+ }
+
+ kvm_vm_free(vm);
+ return 0;
+}
--
2.33.0.1079.g6e70778dc9-goog
