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KVM: selftests: Extend x86's sync_regs_test to check for CR4 races

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Attempt to modify vcpu->run->s.regs _after_ the sanity checks performed by
KVM_CAP_SYNC_REGS's arch/x86/kvm/x86.c:sync_regs().  This can lead to some
nonsensical vCPU states accompanied by kernel splats, e.g. disabling PAE
while long mode is enabled makes KVM all kinds of confused:

 WARNING: CPU: 0 PID: 1142 at arch/x86/kvm/mmu/paging_tmpl.h:358 paging32_walk_addr_generic+0x431/0x8f0 [kvm]

 arch/x86/kvm/mmu/paging_tmpl.h:
 KVM_BUG_ON(is_long_mode(vcpu) && !is_pae(vcpu), vcpu->kvm)

Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://lore.kernel.org/r/20230728001606.2275586-3-mhal@rbox.co
[sean: see link]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Michal Luczaj 2023-07-28 02:12:58 +02:00 committed by Sean Christopherson
parent 0d033770d4
commit ae895cbe61
1 changed files with 72 additions and 0 deletions
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72
tools/testing/selftests/kvm/x86_64/sync_regs_test.c
View File

@ -15,6 +15,7 @@
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <pthread.h>
#include "test_util.h"
#include "kvm_util.h"
@ -80,6 +81,75 @@ static void compare_vcpu_events(struct kvm_vcpu_events *left,
#define TEST_SYNC_FIELDS (KVM_SYNC_X86_REGS|KVM_SYNC_X86_SREGS|KVM_SYNC_X86_EVENTS)
#define INVALID_SYNC_FIELD 0x80000000
/*
* Toggle CR4.PAE while KVM is processing SREGS, EFER.LME=1 with CR4.PAE=0 is
* illegal, and KVM's MMU heavily relies on vCPU state being valid.
*/
static noinline void *race_sregs_cr4(void *arg)
{
struct kvm_run *run = (struct kvm_run *)arg;
__u64 *cr4 = &run->s.regs.sregs.cr4;
__u64 pae_enabled = *cr4;
__u64 pae_disabled = *cr4 & ~X86_CR4_PAE;
for (;;) {
WRITE_ONCE(run->kvm_dirty_regs, KVM_SYNC_X86_SREGS);
WRITE_ONCE(*cr4, pae_enabled);
asm volatile(".rept 512\n\t"
"nop\n\t"
".endr");
WRITE_ONCE(*cr4, pae_disabled);
pthread_testcancel();
}
return NULL;
}
static void race_sync_regs(void *racer)
{
const time_t TIMEOUT = 2; /* seconds, roughly */
struct kvm_translation tr;
struct kvm_vcpu *vcpu;
struct kvm_run *run;
struct kvm_vm *vm;
pthread_t thread;
time_t t;
vm = vm_create_with_one_vcpu(&vcpu, guest_code);
run = vcpu->run;
run->kvm_valid_regs = KVM_SYNC_X86_SREGS;
vcpu_run(vcpu);
run->kvm_valid_regs = 0;
/*
* Selftests run 64-bit guests by default, both EFER.LME and CR4.PAE
* should already be set in guest state.
*/
TEST_ASSERT((run->s.regs.sregs.cr4 & X86_CR4_PAE) &&
(run->s.regs.sregs.efer & EFER_LME),
"vCPU should be in long mode, CR4.PAE=%d, EFER.LME=%d",
!!(run->s.regs.sregs.cr4 & X86_CR4_PAE),
!!(run->s.regs.sregs.efer & EFER_LME));
ASSERT_EQ(pthread_create(&thread, NULL, racer, (void *)run), 0);
for (t = time(NULL) + TIMEOUT; time(NULL) < t;) {
__vcpu_run(vcpu);
if (racer == race_sregs_cr4) {
tr = (struct kvm_translation) { .linear_address = 0 };
__vcpu_ioctl(vcpu, KVM_TRANSLATE, &tr);
}
}
ASSERT_EQ(pthread_cancel(thread), 0);
ASSERT_EQ(pthread_join(thread, NULL), 0);
kvm_vm_free(vm);
}
int main(int argc, char *argv[])
{
struct kvm_vcpu *vcpu;
@ -218,5 +288,7 @@ int main(int argc, char *argv[])
kvm_vm_free(vm);
race_sync_regs(race_sregs_cr4);
return 0;
}