From nobody Mon Feb 9 19:42:27 2026 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E27381ADC71 for ; Sat, 1 Feb 2025 02:17:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738376268; cv=none; b=czaeGzWalvKIZLgVH8efrCeU4PUD7nw0NdswXoRNtfXU8CE/mvCc20Qfu9O4eZX6HQMLNl7zbrstb/poS5rOzpU8G/rCicAHcSXYIru3zxbhklkzfMgCHucXFcqgVfLtVRnXhp9SETEZit4OOYK6+Hnjqbkino8kynTp/Mr8M54= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738376268; c=relaxed/simple; bh=I7ICP95Ld9V+B6MPp3tXCsSnHLq4xQG7ZATAfWkmSSA=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=DwFiHGj/3SozFIiXzUvyRF5oV4Vj3JBUYZayX3poI2XXawJ0Qqtu7e3cs6cA9absqECQghK4uFr+1Jk2Uuw3xG96ICF3FY/AOdIOa3fBIAyE6Whkhvdhb+JGPLvHP2HFa7/tlGEyOmno5HXAtvMnW4S0J7L1cfBsntTw0nVpzys= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=I+zdv+FC; arc=none smtp.client-ip=209.85.214.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="I+zdv+FC" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-2161d5b3eb5so50868905ad.3 for ; Fri, 31 Jan 2025 18:17:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1738376266; x=1738981066; darn=vger.kernel.org; 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=AK/mWgvwJvlM2VErSRU3T5I3ox4v68bEfhNUVA1UAEc=; b=I+zdv+FCyeDWqU0kLUOvk/nmJt/mmLOaIPkGd9fKk3eqlgFdOen7wrBVa+Jl7uqGv8 W0WS1cGB+qD/QjfZYzHw+yYVfPPereyHMsADL+cI5XM5jCbyI4g+DVRZFYDfPz9mtosg DNxkdLmGqlduIuV9X4RBLGfjuBYCq0ENTuOZ0AoyfPM09VwLnl1TDeaE8d3jLrrZAfSN HJHFD1vm4eCbocB9LmehkDWaUa+BZIZsEVdJJ09AvtkGgdmB6iXWtBRv4pSq+MhRW+V5 P1iA3ZThC+0U0drg5FOYMsmn+g001KkAlvMm1MgdWNitNNc/cyMnQvYZZIgVRUOhnhic S68A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1738376266; x=1738981066; 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=AK/mWgvwJvlM2VErSRU3T5I3ox4v68bEfhNUVA1UAEc=; b=h4Ux9HCmcJExyYfImgk/IaD1qlUujxWig/Lh7sJReNZl0OOeOyPf/1VmYdEjuKvVHo ZGH9lwNO+18uzwg+dxjVe2Hwqv1jQt+obg4CQ8aNnfXPdDjAk4dQ5XpwE1A7tE5y13iV wtyW+BwbSSXE8MVGpXggLmIMWJem1/PB33tiwJp4SQpFERQ/iRuJ6wklrvSaZzsMZUXa kdtSsUyzivYspSIMoiQYfTQXGholhY15EbFbd57ghuMruP4eOliDTOSFFrYWkH0Loy7B FmFVk/+mPmsGvOoW+11wExrJl4jMz5YD7K0Z6IQktz0q3jB3bnQSKliDnhNpOahAnOgH KMQw== X-Gm-Message-State: AOJu0Yy7b5nfIB4v7qKCSzSVsd9uX778kspaSHJR4lcKXBNnFU08f/ZQ ZC8xmClv7rUoeVIbncljkuw8XtDbfu5p3LEtIDzjtEdqhSlI41ydaGBx8aW9pNBPxEG8Q/EQ60h bfA== X-Google-Smtp-Source: AGHT+IGIBUdgj+cCgBZpvoXPxY6FOVmtNbk7sDeQo6dqnIl0GeJKfhw5O39y3pDqzJDExNb4JeazGQgwjQ8= X-Received: from pjbdy6.prod.google.com ([2002:a17:90b:6c6:b0:2ef:7483:e770]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:11c3:b0:215:b1a3:4701 with SMTP id d9443c01a7336-21dd7d64c1emr194518565ad.13.1738376266294; Fri, 31 Jan 2025 18:17:46 -0800 (PST) Reply-To: Sean Christopherson Date: Fri, 31 Jan 2025 18:17:13 -0800 In-Reply-To: <20250201021718.699411-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250201021718.699411-1-seanjc@google.com> X-Mailer: git-send-email 2.48.1.362.g079036d154-goog Message-ID: <20250201021718.699411-12-seanjc@google.com> Subject: [PATCH 11/16] x86/paravirt: Don't use a PV sched_clock in CoCo guests with trusted TSC From: Sean Christopherson To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "Kirill A. Shutemov" , Juergen Gross , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Paolo Bonzini , Andy Lutomirski , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, virtualization@lists.linux.dev, linux-hyperv@vger.kernel.org, jailhouse-dev@googlegroups.com, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, Sean Christopherson , Nikunj A Dadhania , Tom Lendacky Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Silently ignore attempts to switch to a paravirt sched_clock when running as a CoCo guest with trusted TSC. In hand-wavy theory, a misbehaving hypervisor could attack the guest by manipulating the PV clock to affect guest scheduling in some weird and/or predictable way. More importantly, reading TSC on such platforms is faster than any PV clock, and sched_clock is all about speed. Signed-off-by: Sean Christopherson --- arch/x86/kernel/paravirt.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index 55c819673a9d..980440d34997 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -88,6 +88,15 @@ DEFINE_STATIC_CALL(pv_sched_clock, native_sched_clock); =20 void __paravirt_set_sched_clock(u64 (*func)(void), bool stable) { + /* + * Don't replace TSC with a PV clock when running as a CoCo guest and + * the TSC is secure/trusted; PV clocks are emulated by the hypervisor, + * which isn't in the guest's TCB. + */ + if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC) || + boot_cpu_has(X86_FEATURE_TDX_GUEST)) + return; + if (!stable) clear_sched_clock_stable(); =20 --=20 2.48.1.362.g079036d154-goog