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selftests: KVM: Add test to verify KVM doesn't explode on "bad" I/O

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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 3b27de2718 ("KVM: x86: split the two parts of emulator_pio_in").

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211025201311.1881846-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-10-25 13:13:11 -07:00 committed by Paolo Bonzini
parent d07898eaf3
commit 10e7a099bf
3 changed files with 116 additions and 0 deletions
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1
tools/testing/selftests/kvm/.gitignore vendored
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@ -30,6 +30,7 @@
/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

1
tools/testing/selftests/kvm/Makefile
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@ -59,6 +59,7 @@ 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

114
tools/testing/selftests/kvm/x86_64/userspace_io_test.c Normal file
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@ -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(&regs, 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, &regs);
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, &regs);
}
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;
}