From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (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 32AB310E0 for ; Thu, 14 Aug 2025 19:05:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755198324; cv=none; b=JXlEAPV3a7JIbQCuc+n+APSkUKWsDYtAq0zd97WR+LhJ0fIOHMM22gXkF8vlzx3u/dn9rGEVmT3IB79de3UCXbDoXWoCE2xy6Qkg+bqB9rM5kZpgbL3Jq3aXB2yuuWBRf8pxIJ04aUDbhxaZ7VmmGq1MdSnUg+J7CUt1udSki1c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755198324; c=relaxed/simple; bh=AN8qz/ITEUM5LRnJa3X9A8S8tftQ2fJgnHqHAaZHT7g=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=LVn6QpERBfSecmaPgSglIXUyLgQf8Sq3UsBs2VyPWaalc/9NJFrygCOUPwf9q/7pBp65xwLZIzAag1RtXSRp8GVPonwTmDQTcfKXjo+888tgUuCyjlqmb65kLDw5azvd6wM/X8DRWbIt6I64pFs1wQjfqTf+8phnpWKR6AxCA2U= 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=MxQJnWs8; arc=none smtp.client-ip=209.85.216.74 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="MxQJnWs8" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-3232677ad11so1245222a91.1 for ; Thu, 14 Aug 2025 12:05:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1755198322; x=1755803122; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=2DFNw3wArC7yOUYWlWO5gneOvkuHKG1tXFsZhvGkvUI=; b=MxQJnWs8uNICgJAdcDgyy9mnNQc/sCo+6pNeKt5o5j5dQf3XIONgAFXQBEkEbbpH06 Z79kWdHHX8vj2VYku15WSbl2ihehjdMIcf/M5PSCFCarQXK2V8oZh8Wk21a5tm6ELWG1 QiVlQN+iHqj/MUMQfwELDg759d4wnxbrZWBLPjJAjJnaT8Rfx6wlvjprZqRhB27yquPr JYMKaFOL+fekRYHdCOjvGqfm7vcTetN8bcht3g0itWVPgoOzuCrUd8ROkxF6JbJJz7mV iFTnNRSQrq9VsXXDn+XCeFCfKleQs8sZlSctSqNXlrdilq0M7LMx8nMgDOKFJrUKkjzK yYCA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1755198322; x=1755803122; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=2DFNw3wArC7yOUYWlWO5gneOvkuHKG1tXFsZhvGkvUI=; b=igi7zBGfK13EgaELFYlWM8MZocPKnRLsG5YL3a2gym0gNWrlT8hLzepjVnWEFLdqyo pDSpn1qlFNEiFYqqkp5QiX3CbH3JTISfTh+MYt7+gXlbjGaEwcHsHSNYEnVZIrWVODct vDVMKUTZ5eyimdtyv7uYnsW3cCUT+NOlVzC3NC5sI/+k6ANqQSrh87nPXbkVvoG0NyGG DqsH26J97SfpvuC6kZR250dkgsOcNF9MQ3B7xcZqQXccIuqujlXImhfTnDI+9MszGCO0 Qex6CIPBiaMdFzv6LkncxC4DdvZM8oShqXBFTLlCPIVFNw38RcWyTzwcLUj4awFmMbrd 3dug== X-Gm-Message-State: AOJu0YysiybQC9XcX19kWP0F4efaQ2StOcb35jw92iOZg/pMf3I7DuxN S8ftisjsHtUGFNQK25DRJmi+oH2+oHv6nhlVdZ8MOBbBaT8+99MIAJl9XGA7/NL3xrdwFq/mXiR rpNZEQw== X-Google-Smtp-Source: AGHT+IH2s+I1TSjeIAje9qDRzYT7oUTiJGlIez0qBhglzuXW+2EZOz+sXrUhTXz8K4L2QNsDcU3DcyVjE4I= X-Received: from pjb12.prod.google.com ([2002:a17:90b:2f0c:b0:321:c2a7:cbce]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:58cf:b0:321:2b8a:430a with SMTP id 98e67ed59e1d1-32327b495f9mr6693312a91.28.1755198322479; Thu, 14 Aug 2025 12:05:22 -0700 (PDT) Date: Thu, 14 Aug 2025 12:05:21 -0700 In-Reply-To: <20250814131146.2093579-2-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <2025081214-bonanza-germproof-173f@gregkh> <20250814131146.2093579-1-sashal@kernel.org> <20250814131146.2093579-2-sashal@kernel.org> Message-ID: Subject: Re: [PATCH 6.6.y 2/3] KVM: nVMX: Check vmcs12->guest_ia32_debugctl on nested VM-Enter From: Sean Christopherson To: Sasha Levin Cc: stable@vger.kernel.org, Maxim Levitsky Content-Type: text/plain; charset="us-ascii" On Thu, Aug 14, 2025, Sasha Levin wrote: > From: Maxim Levitsky > > [ Upstream commit 095686e6fcb4150f0a55b1a25987fad3d8af58d6 ] > > Add a consistency check for L2's guest_ia32_debugctl, as KVM only supports > a subset of hardware functionality, i.e. KVM can't rely on hardware to > detect illegal/unsupported values. Failure to check the vmcs12 value > would allow the guest to load any harware-supported value while running L2. > > Take care to exempt BTF and LBR from the validity check in order to match > KVM's behavior for writes via WRMSR, but without clobbering vmcs12. Even > if VM_EXIT_SAVE_DEBUG_CONTROLS is set in vmcs12, L1 can reasonably expect > that vmcs12->guest_ia32_debugctl will not be modified if writes to the MSR > are being intercepted. > > Arguably, KVM _should_ update vmcs12 if VM_EXIT_SAVE_DEBUG_CONTROLS is set > *and* writes to MSR_IA32_DEBUGCTLMSR are not being intercepted by L1, but > that would incur non-trivial complexity and wouldn't change the fact that > KVM's handling of DEBUGCTL is blatantly broken. I.e. the extra complexity > is not worth carrying. > > Cc: stable@vger.kernel.org > Signed-off-by: Maxim Levitsky > Co-developed-by: Sean Christopherson > Link: https://lore.kernel.org/r/20250610232010.162191-7-seanjc@google.com > Signed-off-by: Sean Christopherson > Stable-dep-of: 7d0cce6cbe71 ("KVM: VMX: Wrap all accesses to IA32_DEBUGCTL with getter/setter APIs") > Signed-off-by: Sasha Levin > --- Acked-by: Sean Christopherson Once again with the caveat that this lands after the RTM_DEBUG patch (which I also acked). https://lore.kernel.org/all/20250813183728.2070321-1-sashal@kernel.org