From nobody Fri Oct 3 18:01:59 2025 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 BE3CF301004 for ; Tue, 26 Aug 2025 23:37:37 +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=1756251459; cv=none; b=a1tCRF+Ivx98Pd8rGLQ2JuKWtaBjiUJSLkA+dP4rXgz8fD6R+N7FiyYVpsdGtE3LN1I8dw0U7H4sP06dAQhAuc9WcDkblZlitum3EUWzjhxomw6HAF2UzUKK4mMSbC+7G9Tm0RMOhI78n7Q+jlDoPT3HJ91rs6G2c2bcPf67HdA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756251459; c=relaxed/simple; bh=j57N/Gk82iBRerXycfBZguqB9r1i9u4OOCcaeL2IZ/k=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=RwSboW0wYUHLXV7zE9HpxOnfVPjEdIVzuUOwyCrVzVwGzM9WHlsPi3eT3Oqf+qe3kWqmmDHr8aekZkOyz8a0bIw4v/C/NGwSVYcYqbDMRh8k1NwNZQZmEYJbu6mf15WRKFqcsf+vXw/zdMvAGjLTT3fcnmoPvYxw1lJ2psOdmRc= 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=med1qlGa; 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="med1qlGa" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-24457ef983fso126283415ad.0 for ; Tue, 26 Aug 2025 16:37:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1756251457; x=1756856257; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:reply-to:from:to:cc :subject:date:message-id:reply-to; bh=XjoQc+0HHdQoYN8CUyvxMw+PJ0TtJn9kjqaYpRARa/o=; b=med1qlGa69yZMBsdwEfWqKVNV0u/iL+5wxbGISOOWzbx0YU6WkyJ4wmiLI59e9cIbW q5jJDWNHB0bIoNkGiu3UC0C8yEBnVVH4JsTiJyxmYTOCyTTpd+J/x4D0C131wdczi+kt cGbIz61MTxRpuiYR2mP6sZX6WvVtCFAIiAeEb/lG1qh+jy9elRfD8MyLA0QxEqTU4mnL UW3t/l5pqTVJIz6pvX+F3+bm602jExYo8a3oNY6az0F0N+6rFOhx//lMt6W5ughGIipa H351qs36OqKxR/SVc15FawJ8C1C2ubfKjumhbrNPVxu/q1ro0FQeh6CUjql0j65yECne M0Xw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1756251457; x=1756856257; h=cc:to:from:subject:message-id:mime-version:date:reply-to :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=XjoQc+0HHdQoYN8CUyvxMw+PJ0TtJn9kjqaYpRARa/o=; b=uMFzlRMZCsN+OWfNqf64/ZSbTovezr7Yy7FxO/V5WOUd7QKi4zUzQLIlYO9bvDgGvv Anm/q3jjzFI3aMkiZhokA1Meo4eIekbZRfkEzT4ZFyOuFIVjtrKV5DMZkcDW/AjoHu6j VjDcv8y/0TOGdaYhWiwmwYPnGNDFZ9/tGhzuOm66HM/oj1qBH+d6DBKp1jg08bpnx6I9 hcUIN4xuCoKv+AR+qWlv1w7fnBAcwjUkRB+14y9QTDG+GfjXD0CDoGVf6lEGATcDnpc6 ag79fEJ80I0I5q9ruTaV7jVBfeF9OasQmj/eu2qoiNjJuSHfnSjf0Nx9QkJZhU5xKigf 6ViA== X-Forwarded-Encrypted: i=1; AJvYcCVn0rHNgqX/oPhoatAt2ji7ChGF0n6y7NnU8/DOGCZ6pNCab07DC9a5Rqkw1XX2+Gj3BJJuj30a5ZnxBDM=@vger.kernel.org X-Gm-Message-State: AOJu0Yzgoq9/Hf46g97d+fd7Np54Nadx+1QFIHVyb6E28jiD9FbHlIag Zi5V+rW4H3ZZ2VbEYHB4nfDu4U6MNpOYlvsAjlSGmq4N28LjLjYlx+XqVOEvsCRrh/zEDvYuJBT 0jYkJyg== X-Google-Smtp-Source: AGHT+IHFcFV7G2qwiXBjY3JxXFXbDIce6OGwarZ3EB+aa4VM9or737yUcUD+ZQ6zcGFGrv2dxeZBVUYrzgs= X-Received: from plbke15.prod.google.com ([2002:a17:903:340f:b0:234:c2e4:1df6]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:ef4f:b0:246:571:4b22 with SMTP id d9443c01a7336-2462ef49f48mr233105655ad.59.1756251456668; Tue, 26 Aug 2025 16:37:36 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 26 Aug 2025 16:37:34 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.51.0.268.g9569e192d0-goog Message-ID: <20250826233734.4011090-1-seanjc@google.com> Subject: [PATCH] KVM: SEV: Reject non-positive effective lengths during LAUNCH_UPDATE From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Lendacky , Michael Roth Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Check for an invalid length during LAUNCH_UPDATE at the start of snp_launch_update() instead of subtly relying on kvm_gmem_populate() to detect the bad state. Code that directly handles userspace input absolutely should sanitize those inputs; failure to do so is asking for bugs where KVM consumes an invalid "npages". Keep the check in gmem, but wrap it in a WARN to flag any bad usage by the caller. Note, this is technically an ABI change as KVM would previously allow a length of '0'. But allowing a length of '0' is nonsensical and creates pointless conundrums in KVM. E.g. an empty range is arguably neither private nor shared, but LAUNCH_UPDATE will fail if the starting gpa can't be made private. In practice, no known or well-behaved VMM passes a length of '0'. Cc: Thomas Lendacky Cc: Michael Roth Signed-off-by: Sean Christopherson --- Compile tested only. Came across this when trying to figure out how to handle the batching of gmem post-populate calls. arch/x86/kvm/svm/sev.c | 2 ++ virt/kvm/guest_memfd.c | 3 ++- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index f4381878a9e5..746a57bf1f71 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2360,6 +2360,8 @@ static int snp_launch_update(struct kvm *kvm, struct = kvm_sev_cmd *argp) return -EINVAL; =20 npages =3D params.len / PAGE_SIZE; + if (npages <=3D 0) + return -EINVAL; =20 /* * For each GFN that's being prepared as part of the initial guest diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 7d85cc33c0bb..79552467add5 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -639,7 +639,8 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn= , void __user *src, long long i; =20 lockdep_assert_held(&kvm->slots_lock); - if (npages < 0) + + if (WARN_ON_ONCE(npages <=3D 0)) return -EINVAL; =20 slot =3D gfn_to_memslot(kvm, start_gfn); base-commit: ecbcc2461839e848970468b44db32282e5059925 --=20 2.51.0.268.g9569e192d0-goog