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From: Oliver Upton To: Sean Christopherson Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Jones , Anup Patel , Atish Patra , Christian Borntraeger , Janosch Frank , Claudio Imbrenda Subject: Re: [PATCH 4/5] KVM: selftests: Explicitly verify KVM doesn't patch hypercall if quirk==off Message-ID: References: <20220908233134.3523339-1-seanjc@google.com> <20220908233134.3523339-5-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220908233134.3523339-5-seanjc@google.com> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > .../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 >