From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DA52DEB64DD for ; Sat, 29 Jul 2023 00:37:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233739AbjG2AhA (ORCPT ); Fri, 28 Jul 2023 20:37:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57898 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232887AbjG2Agx (ORCPT ); Fri, 28 Jul 2023 20:36:53 -0400 Received: from mail-pg1-x54a.google.com (mail-pg1-x54a.google.com [IPv6:2607:f8b0:4864:20::54a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7231430FB for ; Fri, 28 Jul 2023 17:36:52 -0700 (PDT) Received: by mail-pg1-x54a.google.com with SMTP id 41be03b00d2f7-55c04f5827eso1882186a12.1 for ; Fri, 28 Jul 2023 17:36:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1690591012; x=1691195812; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=jjZUurEgx8+1WTff2yy2mIJojJc3waWamxg7HHxYGIg=; b=noxRP7DyXhyaM98FK0Vfbiwdsje2k4Fme8Ej+Lzw3561F5KC+8wOpq147aZ9YkCJA4 yEvYhRIL0tZYxlGfadJ3T/3jLoEbUzrRLhc+Tpjjx3RoDw70wdOdllOhL6e3s9wXinRE stWTzC1jd5xpvinZznJG2aox3Q/eCKj8CKm8HHcFpRAqbyrWnYRMbc+qOK3bW954IHkN khHcPSsUb+qRbsTCBupFaUGuJ2ouREB28Jz6YQlS/pAikuObTfZ9xuQkb79Ykk1rItdc /QIdsA7sAOkNbdhQEtraNqyeGeOjcd1g1go1jvyob4nqQ1d1fjXGQ7+U7YBmsRRKafg/ r2oA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690591012; x=1691195812; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=jjZUurEgx8+1WTff2yy2mIJojJc3waWamxg7HHxYGIg=; b=TakbQ+TOILS49LyaXF/6cFBF5lBrZSr5B+XSmro4ZgGZnkss+NCSgBKxCZXk6qx0/K 6GEjcs71bQvRMrzN6Yf/MHoU8j6KqRAYckjafUyfhpk5zkG9R/DdyQ7JJFL/qbSulrUa LagWGwALk1ms6h+PzXhKZhpiUP39AVLfb7wlP/xi3nD8c0qc8Wv3yZUfDVzfkTv/O0Pr TUsM6auN/r8iEVEBYQjvrCjs4pEYUUfb4yAL0iErlcyOCDymNFDQfnA2u7poUNL9H081 yPb3WxUK6GWn4XOEb8r6LtW1cK+2NNFubWJpP3XxIGNRGcR+l1xyfKUSfo8/nw0NcOxi HkPw== X-Gm-Message-State: ABy/qLZzrkPLfjuAo0wFcUfY28hRh1KSPDpKr5zeQmt4cHs05xzI8L3a mFBGC4wum8ku7ueUgWvEjksDK8rD/Wk= X-Google-Smtp-Source: APBJJlGOQzm3R4lKKE8dcYLKl/QqgICXHzOASeCmeTU7bt0Nk1iWBuRrxrxWvMsBrvIEj9CQ6afqhQgcvVk= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:902:f990:b0:1b8:80c9:a98e with SMTP id ky16-20020a170902f99000b001b880c9a98emr10492plb.13.1690591012012; Fri, 28 Jul 2023 17:36:52 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 28 Jul 2023 17:36:12 -0700 In-Reply-To: <20230729003643.1053367-1-seanjc@google.com> Mime-Version: 1.0 References: <20230729003643.1053367-1-seanjc@google.com> X-Mailer: git-send-email 2.41.0.487.g6d72f3e995-goog Message-ID: <20230729003643.1053367-4-seanjc@google.com> Subject: [PATCH v4 03/34] KVM: selftests: Add a shameful hack to preserve/clobber GPRs across ucall From: Sean Christopherson To: Paolo Bonzini , Marc Zyngier , Oliver Upton , Christian Borntraeger , Janosch Frank , Claudio Imbrenda Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Sean Christopherson , Thomas Huth , "=?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?=" , Aaron Lewis Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Preserve or clobber all GPRs (except RIP and RSP, as they're saved and restored via the VMCS) when performing a ucall on x86 to fudge around a horrific long-standing bug in selftests' nested VMX support where L2's GPRs are not preserved across a nested VM-Exit. I.e. if a test triggers a nested VM-Exit to L1 in response to a ucall, e.g. GUEST_SYNC(), then L2's GPR state can be corrupted. The issues manifests as an unexpected #GP in clear_bit() when running the hyperv_evmcs test due to RBX being used to track the ucall object, and RBX being clobbered by the nested VM-Exit. The problematic hyperv_evmcs testcase is where L0 (test's host userspace) injects an NMI in response to GUEST_SYNC(8) from L2, but the bug could "randomly" manifest in any test that induces a nested VM-Exit from L0. The bug hasn't caused failures in the past due to sheer dumb luck. The obvious fix is to rework the nVMX helpers to save/restore L2 GPRs across VM-Exit and VM-Enter, but that is a much bigger task and carries its own risks, e.g. nSVM does save/restore GPRs, but not in a thread-safe manner, and there is a _lot_ of cleanup that can be done to unify code for doing VM-Enter on nVMX, nSVM, and eVMCS. Signed-off-by: Sean Christopherson --- .../testing/selftests/kvm/lib/x86_64/ucall.c | 32 +++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/kvm/lib/x86_64/ucall.c b/tools/testing/selftests/kvm/lib/x86_64/ucall.c index 4d41dc63cc9e..a53df3ece2f8 100644 --- a/tools/testing/selftests/kvm/lib/x86_64/ucall.c +++ b/tools/testing/selftests/kvm/lib/x86_64/ucall.c @@ -14,8 +14,36 @@ void ucall_arch_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa) void ucall_arch_do_ucall(vm_vaddr_t uc) { - asm volatile("in %[port], %%al" - : : [port] "d" (UCALL_PIO_PORT), "D" (uc) : "rax", "memory"); + /* + * FIXME: Revert this hack (the entire commit that added it) once nVMX + * preserves L2 GPRs across a nested VM-Exit. If a ucall from L2, e.g. + * to do a GUEST_SYNC(), lands the vCPU in L1, any and all GPRs can be + * clobbered by L1. Save and restore non-volatile GPRs (clobbering RBP + * in particular is problematic) along with RDX and RDI (which are + * inputs), and clobber volatile GPRs. *sigh* + */ +#define HORRIFIC_L2_UCALL_CLOBBER_HACK \ + "rcx", "rsi", "r8", "r9", "r10", "r11" + + asm volatile("push %%rbp\n\t" + "push %%r15\n\t" + "push %%r14\n\t" + "push %%r13\n\t" + "push %%r12\n\t" + "push %%rbx\n\t" + "push %%rdx\n\t" + "push %%rdi\n\t" + "in %[port], %%al\n\t" + "pop %%rdi\n\t" + "pop %%rdx\n\t" + "pop %%rbx\n\t" + "pop %%r12\n\t" + "pop %%r13\n\t" + "pop %%r14\n\t" + "pop %%r15\n\t" + "pop %%rbp\n\t" + : : [port] "d" (UCALL_PIO_PORT), "D" (uc) : "rax", "memory", + HORRIFIC_L2_UCALL_CLOBBER_HACK); } void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu) -- 2.41.0.487.g6d72f3e995-goog