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Tsirkin" , Ani Sinha , Xiao Guangrong , Daniel Henrique Barboza , Greg Kurz , Eric Blake , Markus Armbruster , Eduardo Habkost Subject: Re: [PATCH v2 1/9] nvdimm: Reject writing label data to ROM instead of crashing QEMU Message-ID: <20230822192539.GQ727224@fedora> References: <20230822114504.239505-1-david@redhat.com> <20230822114504.239505-2-david@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="M8WIBXyRbKTDxuLq" Content-Disposition: inline In-Reply-To: <20230822114504.239505-2-david@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --M8WIBXyRbKTDxuLq Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Aug 22, 2023 at 01:44:49PM +0200, David Hildenbrand wrote: > Currently, when using a true R/O NVDIMM (ROM memory backend) with a label > area, the VM can easily crash QEMU by trying to write to the label area, > because the ROM memory is mmap'ed without PROT_WRITE. >=20 > [root@vm-0 ~]# ndctl disable-region region0 > disabled 1 region > [root@vm-0 ~]# ndctl zero-labels nmem0 > -> QEMU segfaults >=20 > Let's remember whether we have a ROM memory backend and properly > reject the write request: >=20 > [root@vm-0 ~]# ndctl disable-region region0 > disabled 1 region > [root@vm-0 ~]# ndctl zero-labels nmem0 > zeroed 0 nmem >=20 > In comparison, on a system with a R/W NVDIMM: >=20 > [root@vm-0 ~]# ndctl disable-region region0 > disabled 1 region > [root@vm-0 ~]# ndctl zero-labels nmem0 > zeroed 1 nmem >=20 > For ACPI, just return "unsupported", like if no label exists. For spapr, > return "H_P2", similar to when no label area exists. >=20 > Could we rely on the "unarmed" property? Maybe, but it looks cleaner to > only disallow what certainly cannot work. >=20 > After all "unarmed=3Don" primarily means: cannot accept persistent writes= =2E In > theory, there might be setups where devices with "unarmed=3Don" set could > be used to host non-persistent data (temporary files, system RAM, ...); f= or > example, in Linux, admins can overwrite the "readonly" setting and still > write to the device -- which will work as long as we're not using ROM. > Allowing writing label data in such configurations can make sense. >=20 > Fixes: dbd730e85987 ("nvdimm: check -object memory-backend-file, readonly= =3Don option") > Signed-off-by: David Hildenbrand > --- > hw/acpi/nvdimm.c | 11 ++++++++--- > hw/mem/nvdimm.c | 10 +++++++--- > hw/ppc/spapr_nvdimm.c | 3 ++- > include/hw/mem/nvdimm.h | 6 ++++++ > 4 files changed, 23 insertions(+), 7 deletions(-) Reviewed-by: Stefan Hajnoczi --M8WIBXyRbKTDxuLq Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmTlC7IACgkQnKSrs4Gr c8gjvAf/TNdp42RIHSwGsRfntN+3wJs2Q8zCTqwpakKZeWDlJKBrUE9r+yVKiguF aSAlgp0aKNdAchjkEkGsHG08xrqynGQV97xdIXjbWtFQutph4Co6HhV0E14pi6JS N/7TZnYjwGyVr39Ob7kr9XZKYaFK/08c8DocDo3g0FfZFlsIiTpyNA1cOYNVUwfB w6JO7DgOtSKHmLgxLRisdi/xsQmZk00DuiPQ6YsvDe4aS0e5ER3E/nwwWUq77+Y9 3dUUNVxKdCaoz7tdTaeIE3N6FI8l9Qw9NhmMvNnB2bJHEkvcKYIwMBI8fahrAd9i IHDC70wZF5yOWxjMk1xV8sHrGoTKnQ== =EAIM -----END PGP SIGNATURE----- --M8WIBXyRbKTDxuLq--