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[PATCH 4/5] KVM: selftests: Explicitly verify KVM doesn't patch hypercall if quirk==off

Sean Christopherson posted 5 patches 3 years, 6 months ago
There is a newer version of this series
[PATCH 4/5] KVM: selftests: Explicitly verify KVM doesn't patch hypercall if quirk==off
Posted by Sean Christopherson 3 years, 6 months ago 
Explicitly verify that KVM doesn't patch in the native hypercall if the
FIX_HYPERCALL_INSN quirk is disabled.  The test currently verifies that
a #UD occurred, but doesn't actually verify that no patching occurred.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 .../selftests/kvm/x86_64/fix_hypercall_test.c | 35 ++++++++++++++-----
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c b/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c
index dde97be3e719..5925da3b3648 100644
--- a/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c
+++ b/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c
@@ -21,8 +21,8 @@ static bool ud_expected;
 
 static void guest_ud_handler(struct ex_regs *regs)
 {
-	GUEST_ASSERT(ud_expected);
-	GUEST_DONE();
+	regs->rax = -EFAULT;
+	regs->rip += HYPERCALL_INSN_SIZE;
 }
 
 extern unsigned char svm_hypercall_insn[HYPERCALL_INSN_SIZE];
@@ -57,17 +57,18 @@ static void guest_main(void)
 {
 	unsigned char *native_hypercall_insn, *hypercall_insn;
 	uint8_t apic_id;
+	uint64_t ret;
 
 	apic_id = GET_APIC_ID_FIELD(xapic_read_reg(APIC_ID));
 
 	if (is_intel_cpu()) {
 		native_hypercall_insn = vmx_hypercall_insn;
 		hypercall_insn = svm_hypercall_insn;
-		svm_do_sched_yield(apic_id);
+		ret = svm_do_sched_yield(apic_id);
 	} else if (is_amd_cpu()) {
 		native_hypercall_insn = svm_hypercall_insn;
 		hypercall_insn = vmx_hypercall_insn;
-		vmx_do_sched_yield(apic_id);
+		ret = vmx_do_sched_yield(apic_id);
 	} else {
 		GUEST_ASSERT(0);
 		/* unreachable */
@@ -75,12 +76,28 @@ static void guest_main(void)
 	}
 
 	/*
-	 * The hypercall didn't #UD (guest_ud_handler() signals "done" if a #UD
-	 * occurs).  Verify that a #UD is NOT expected and that KVM patched in
-	 * the native hypercall.
+	 * If the quirk is disabled, verify that guest_ud_handler() "returned"
+	 * -EFAULT and that KVM did NOT patch the hypercall.  If the quirk is
+	 * enabled, verify that the hypercall succeeded and that KVM patched in
+	 * the "right" hypercall.
 	 */
-	GUEST_ASSERT(!ud_expected);
-	GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn, HYPERCALL_INSN_SIZE));
+	if (ud_expected) {
+		GUEST_ASSERT(ret == (uint64_t)-EFAULT);
+
+		/*
+		 * Divergence should occur only on the last byte, as the VMCALL
+		 * (0F 01 C1) and VMMCALL (0F 01 D9) share the first two bytes.
+		 */
+		GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn,
+				     HYPERCALL_INSN_SIZE - 1));
+		GUEST_ASSERT(memcmp(native_hypercall_insn, hypercall_insn,
+				    HYPERCALL_INSN_SIZE));
+	} else {
+		GUEST_ASSERT(!ret);
+		GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn,
+			     HYPERCALL_INSN_SIZE));
+	}
+
 	GUEST_DONE();
 }
 
-- 
2.37.2.789.g6183377224-goog
Re: [PATCH 4/5] KVM: selftests: Explicitly verify KVM doesn't patch hypercall if quirk==off
Posted by Oliver Upton 3 years, 6 months ago 
On Thu, Sep 08, 2022 at 11:31:33PM +0000, Sean Christopherson wrote:
> Explicitly verify that KVM doesn't patch in the native hypercall if the
> FIX_HYPERCALL_INSN quirk is disabled.  The test currently verifies that
> a #UD occurred, but doesn't actually verify that no patching occurred.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  .../selftests/kvm/x86_64/fix_hypercall_test.c | 35 ++++++++++++++-----
>  1 file changed, 26 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c b/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c
> index dde97be3e719..5925da3b3648 100644
> --- a/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c
> @@ -21,8 +21,8 @@ static bool ud_expected;
>  
>  static void guest_ud_handler(struct ex_regs *regs)
>  {
> -	GUEST_ASSERT(ud_expected);
> -	GUEST_DONE();
> +	regs->rax = -EFAULT;
> +	regs->rip += HYPERCALL_INSN_SIZE;
>  }
>  
>  extern unsigned char svm_hypercall_insn[HYPERCALL_INSN_SIZE];
> @@ -57,17 +57,18 @@ static void guest_main(void)
>  {
>  	unsigned char *native_hypercall_insn, *hypercall_insn;
>  	uint8_t apic_id;
> +	uint64_t ret;
>  
>  	apic_id = GET_APIC_ID_FIELD(xapic_read_reg(APIC_ID));
>  
>  	if (is_intel_cpu()) {
>  		native_hypercall_insn = vmx_hypercall_insn;
>  		hypercall_insn = svm_hypercall_insn;
> -		svm_do_sched_yield(apic_id);
> +		ret = svm_do_sched_yield(apic_id);
>  	} else if (is_amd_cpu()) {
>  		native_hypercall_insn = svm_hypercall_insn;
>  		hypercall_insn = vmx_hypercall_insn;
> -		vmx_do_sched_yield(apic_id);
> +		ret = vmx_do_sched_yield(apic_id);
>  	} else {
>  		GUEST_ASSERT(0);
>  		/* unreachable */
> @@ -75,12 +76,28 @@ static void guest_main(void)
>  	}
>  
>  	/*
> -	 * The hypercall didn't #UD (guest_ud_handler() signals "done" if a #UD
> -	 * occurs).  Verify that a #UD is NOT expected and that KVM patched in
> -	 * the native hypercall.
> +	 * If the quirk is disabled, verify that guest_ud_handler() "returned"
> +	 * -EFAULT and that KVM did NOT patch the hypercall.  If the quirk is
> +	 * enabled, verify that the hypercall succeeded and that KVM patched in
> +	 * the "right" hypercall.
>  	 */
> -	GUEST_ASSERT(!ud_expected);
> -	GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn, HYPERCALL_INSN_SIZE));
> +	if (ud_expected) {
> +		GUEST_ASSERT(ret == (uint64_t)-EFAULT);
> +
> +		/*
> +		 * Divergence should occur only on the last byte, as the VMCALL
> +		 * (0F 01 C1) and VMMCALL (0F 01 D9) share the first two bytes.
> +		 */
> +		GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn,
> +				     HYPERCALL_INSN_SIZE - 1));
> +		GUEST_ASSERT(memcmp(native_hypercall_insn, hypercall_insn,
> +				    HYPERCALL_INSN_SIZE));

Should we just keep the assertions consistent for both cases (patched
and unpatched)?

--
Thanks,
Oliver

> +	} else {
> +		GUEST_ASSERT(!ret);
> +		GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn,
> +			     HYPERCALL_INSN_SIZE));
> +	}
> +
>  	GUEST_DONE();
>  }
>  
> -- 
> 2.37.2.789.g6183377224-goog
>
Re: [PATCH 4/5] KVM: selftests: Explicitly verify KVM doesn't patch hypercall if quirk==off
Posted by Sean Christopherson 3 years, 6 months ago 
On Mon, Sep 19, 2022, Oliver Upton wrote:
> On Thu, Sep 08, 2022 at 11:31:33PM +0000, Sean Christopherson wrote:
> > @@ -75,12 +76,28 @@ static void guest_main(void)
> >  	}
> >  
> >  	/*
> > -	 * The hypercall didn't #UD (guest_ud_handler() signals "done" if a #UD
> > -	 * occurs).  Verify that a #UD is NOT expected and that KVM patched in
> > -	 * the native hypercall.
> > +	 * If the quirk is disabled, verify that guest_ud_handler() "returned"
> > +	 * -EFAULT and that KVM did NOT patch the hypercall.  If the quirk is
> > +	 * enabled, verify that the hypercall succeeded and that KVM patched in
> > +	 * the "right" hypercall.
> >  	 */
> > -	GUEST_ASSERT(!ud_expected);
> > -	GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn, HYPERCALL_INSN_SIZE));
> > +	if (ud_expected) {
> > +		GUEST_ASSERT(ret == (uint64_t)-EFAULT);
> > +
> > +		/*
> > +		 * Divergence should occur only on the last byte, as the VMCALL
> > +		 * (0F 01 C1) and VMMCALL (0F 01 D9) share the first two bytes.
> > +		 */
> > +		GUEST_ASSERT(!memcmp(native_hypercall_insn, hypercall_insn,
> > +				     HYPERCALL_INSN_SIZE - 1));
> > +		GUEST_ASSERT(memcmp(native_hypercall_insn, hypercall_insn,
> > +				    HYPERCALL_INSN_SIZE));
> 
> Should we just keep the assertions consistent for both cases (patched
> and unpatched)?

Not sure I follow what you're suggesting.  By "consistent" do you mean doing
something like snapshotting hypercall_insn and verifying that it's not changed?

Patchew 2.1-devel-ea86937

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