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Donenfeld" , James Bottomley , Gerd Hoffmann , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= , "H. Peter Anvin" , Paolo Bonzini , Richard Henderson , Eduardo Habkost , "Michael S. Tsirkin" , Marcel Apfelbaum , Tobin Feldman-Fitzthum Subject: [PATCH] x86: Don't add RNG seed to Linux cmdline for SEV guests Date: Tue, 7 Feb 2023 08:41:16 +0000 Message-Id: <20230207084116.285787-1-dovmurik@linux.ibm.com> X-Mailer: git-send-email 2.25.1 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: RrffsNN6QPZzDuNo5_5AByA9ugaYkdqF X-Proofpoint-ORIG-GUID: u56_dapRxGFjLFlZABxxGt6a9xm0o8fO X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.122.1 definitions=2023-02-07_02,2023-02-06_03,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 lowpriorityscore=0 malwarescore=0 adultscore=0 priorityscore=1501 phishscore=0 suspectscore=0 mlxlogscore=999 bulkscore=0 mlxscore=0 spamscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2302070077 Received-SPF: pass client-ip=148.163.156.1; envelope-from=dovmurik@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Recent feature to supply RNG seed to the guest kernel modifies the kernel command-line by adding extra data at its end; this breaks measured boot with SEV and OVMF, and possibly signed boot. Specifically SEV doesn't miss this feature because it uses UEFI/OVMF which has its own way of getting random seed (not to mention that getting the random seed from the untrusted host breaks the confidential computing trust model). Disable the RNG seed feature in SEV guests. Fixes: eac7a7791bb6 ("x86: don't let decompressed kernel image clobber setup_data") Reported-by: Tom Lendacky Signed-off-by: Dov Murik --- There might be a need for a wider change to the ways setup_data entries are handled in x86_load_linux(); here I just try to restore the situation for SEV guests prior to the addition of the SETUP_RNG_SEED entry. Recent discussions on other (safer?) ways to pass this setup_data entry: [1] https://lore.kernel.org/qemu-devel/da39abab9785aea2a2e7652ed6403b6268aeb31f.camel@linux.ibm.com/ Note that in qemu 7.2.0 this is broken as well -- there the SETUP_RNG_SEED entry is appended to the Linux kernel data (and therefore modifies and breaks the measurement of the kernel in SEV measured boot). A similar fix will be needed there (but I fear this patch cannot be applied as-is). --- hw/i386/x86.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) base-commit: 6661b8c7fe3f8b5687d2d90f7b4f3f23d70e3e8b diff --git a/hw/i386/x86.c b/hw/i386/x86.c index eaff4227bd..e65a83f8df 100644 --- a/hw/i386/x86.c +++ b/hw/i386/x86.c @@ -1103,7 +1103,7 @@ void x86_load_linux(X86MachineState *x86ms, load_image_size(dtb_filename, setup_data->data, dtb_size); } - if (!legacy_no_rng_seed && protocol >= 0x209) { + if (!legacy_no_rng_seed && protocol >= 0x209 && !sev_enabled()) { setup_data_offset = cmdline_size; cmdline_size += sizeof(SetupData) + RNG_SEED_LENGTH; kernel_cmdline = g_realloc(kernel_cmdline, cmdline_size);