From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (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 B9C9923534A for ; Thu, 27 Feb 2025 02:19:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740622797; cv=none; b=YC07fUgcWvxVrJ4soVFQ7rLvhXCXHteyq3SFGMPgQnuvb68VMRMUm9wn9qhOxhZqggzCu9g+MLky7QwNTvXQspmtpabqAmxIt5JyYCiCRnIFszdW5sbNn0drsfembLaHKqO1q+JVkxtiA6ayG8TqWhIMdMbA5doJQUDJwd2dpoQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740622797; c=relaxed/simple; bh=9PNQlaFr17QsW09OA3IEH/cFSTquMC7pYNcyhSay2n0=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=HYscxsRHDWYLP+zB4FwmDdfA7YTE6k0/Cg+dwPXyKse4Efzkm6YGFgXL7CvHdruGUaeGKwF0vm/OyT16hTDYVfQ3o5DIn90Ms0P/kz2lihRA9Ej83Kifn46OOocu2uu2hmfyWgezD3dIJV7whxE6xMKHWiftsQNEIykhpKDnG70= 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=cmAjvxme; arc=none smtp.client-ip=209.85.216.73 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="cmAjvxme" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-2fe86c01f5cso1042427a91.1 for ; Wed, 26 Feb 2025 18:19:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1740622795; x=1741227595; darn=lists.linux.dev; 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=3F6YIZD9bSIlkGuU2KG3Ao1xkSJhhKmqbmLiePXFSIM=; b=cmAjvxmeLsldBT+QOQrdOaQ5D2i3k3QBVTbtK2EHoKZX2monppob8OvpAsaqq9tfqg jPK56vDkI4vI+l6RFSYczfmtb3Od72P7OG+W1d/gmtfe2aSLBsmpLAvWS56uf07FJihH H48ca87f0nC7YB+oU5vIsd85sXSYp0dGVmHiSEobsoGObrS4ZvcQjBqWK4IhlzfiQb6h s49M8LlwOtePIqo/bla7OaL2MkWqrx9ok0D6Y06VoYym6Hy/8rxDNdobZgme2Bc2kvNQ NfJU35c3VYEzkbCY79OKAsr+8xYvpYQBYjc9Dr2rRIOVoNqETSjGLfgkyT4oA++yxyO2 4BaA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740622795; x=1741227595; 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=3F6YIZD9bSIlkGuU2KG3Ao1xkSJhhKmqbmLiePXFSIM=; b=TEsuBDAXZgYpkqIAq0TkNchCQ5GD+p2rBVgGfj3lXxCoRK7dg/rXyDHfH4TNv9VYWC 0vF1cEZh1HFKaT+yQ8ctx9BDKXNk1JQJd4+VXNCb+HZa+b9Pn86bksi6QmXrrz0hMGa8 8jtitZWvcnH+Z4xxFZ+YnOpg7MR+NSQCg/dH4ytrQEfy19SxeNcDLBmBWOt3ZUalCxAI VUoZTiSO2PChMVUKoceYilzQhW9KG1Qtk4VXhJvx0e0SGvQyHqxJx8zshdq+XIGKUTur +5TZ6TLwobvwWWJ3zxFT1vqSdNUIW25cPQq6HT44unU0IIx0yggqgcta+VyPLHhthTk3 iA1A== X-Forwarded-Encrypted: i=1; AJvYcCVj1UfIBW4X0lZAZOVULxLVXmF4gfcvzI5RdLlkSNM1UVUouM6hkL1KHLFADNHl+3jz4WtmnYCx5Hs4@lists.linux.dev X-Gm-Message-State: AOJu0YxiXmHRwKL+JcvbLMpTEKxveJt3yYeLSE3YmHXUjJcVAYERFgz8 V7EZbKZC90Xh2N9DUD5FXVg/XuPTHI+ob50wsR61mPlnvUC8MYiUrnuh/ssZkdMjlwmA22MzvOf MlA== X-Google-Smtp-Source: AGHT+IGJ6z3saIzRbkZlSBZLnZw7mlbnCfDCjtlOA/kyHI3FVoB/Y5gfMuQ1H6WQ1/ZAhh6gzh0XRDRpGl4= X-Received: from pfbfb4.prod.google.com ([2002:a05:6a00:2d84:b0:732:1ead:f8ac]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:1509:b0:1f2:e2b0:dd91 with SMTP id adf61e73a8af0-1f2e2b0ddb7mr3698859637.21.1740622795028; Wed, 26 Feb 2025 18:19:55 -0800 (PST) Reply-To: Sean Christopherson Date: Wed, 26 Feb 2025 18:18:46 -0800 In-Reply-To: <20250227021855.3257188-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250227021855.3257188-1-seanjc@google.com> X-Mailer: git-send-email 2.48.1.711.g2feabab25a-goog Message-ID: <20250227021855.3257188-31-seanjc@google.com> Subject: [PATCH v2 30/38] 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" , Paolo Bonzini , Sean Christopherson , Juergen Gross , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Ajay Kaher , Jan Kiszka , Andy Lutomirski , Peter Zijlstra , Daniel Lezcano , John Stultz Cc: linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, virtualization@lists.linux.dev, linux-hyperv@vger.kernel.org, xen-devel@lists.xenproject.org, Tom Lendacky , Nikunj A Dadhania 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 a3a1359cfc26..c538c608d9fb 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -89,6 +89,15 @@ DEFINE_STATIC_CALL(pv_sched_clock, native_sched_clock); int __init __paravirt_set_sched_clock(u64 (*func)(void), bool stable, void (*save)(void), void (*restore)(void)) { + /* + * 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 -EPERM; + if (!stable) clear_sched_clock_stable(); -- 2.48.1.711.g2feabab25a-goog