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Fri, 21 Feb 2025 15:42:15 +0000 (GMT) Message-ID: <1883119129dbeeabad1f5239f042a7b920feef0f.camel@linux.ibm.com> Subject: Re: [PATCH v8 3/7] ima: kexec: skip IMA segment validation after kexec soft reboot From: Mimi Zohar To: steven chen , stefanb@linux.ibm.com, roberto.sassu@huaweicloud.com, roberto.sassu@huawei.com, eric.snowberg@oracle.com, ebiederm@xmission.com, paul@paul-moore.com, code@tyhicks.com, bauermann@kolabnow.com, linux-integrity@vger.kernel.org, kexec@lists.infradead.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Cc: madvenka@linux.microsoft.com, nramas@linux.microsoft.com, James.Bottomley@HansenPartnership.com, bhe@redhat.com, vgoyal@redhat.com, dyoung@redhat.com Date: Fri, 21 Feb 2025 10:41:59 -0500 In-Reply-To: <20250218225502.747963-4-chenste@linux.microsoft.com> References: <20250218225502.747963-1-chenste@linux.microsoft.com> <20250218225502.747963-4-chenste@linux.microsoft.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 (3.52.4-2.fc40) Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: QCsQPTOODc6JC0-pUekND63em9iiktCZ X-Proofpoint-GUID: QCsQPTOODc6JC0-pUekND63em9iiktCZ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-21_05,2025-02-20_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 clxscore=1015 spamscore=0 lowpriorityscore=0 adultscore=0 phishscore=0 mlxscore=0 impostorscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502100000 definitions=main-2502210111 On Tue, 2025-02-18 at 14:54 -0800, steven chen wrote: > kexec_calculate_store_digests() calculates and stores the digest of the > segment at kexec_file_load syscall where the IMA segment is also > allocated.=C2=A0 With this series, the IMA segment will be updated with t= he > measurement log at kexec execute stage when soft reboot is initiated.=20 > Therefore, it may fail digest verification in verify_sha256_digest()=20 > after kexec soft reboot into the new kernel. Therefore, the digest=20 > calculation/verification of the IMA segment needs to be skipped. >=20 > Skip the calculating and storing digest of the IMA segment in > kexec_calculate_store_digests() so that it is not added to the > 'purgatory_sha_regions'. >=20 > Since verify_sha256_digest() only verifies 'purgatory_sha_regions', > no change is needed in verify_sha256_digest() in this context. >=20 > With this change, the IMA segment is not included in the digest > calculation, storage, and verification. Basically you're saying because the hash verification will fail, don't incl= ude the IMA buffer. What's missing is the reason for not caring whether the IM= A hash is included or not. I understand this is the best we can do without making some major kexec cha= nges. >=20 > Signed-off-by: Tushar Sugandhi > Signed-off-by: steven chen > Reviewed-by: Stefan Berger After updating the patch description, Reviewed-by: Mimi Zohar > --- > =C2=A0include/linux/kexec.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 3 +++ > =C2=A0kernel/kexec_file.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | 22 ++++++++++++++++++++++ > =C2=A0security/integrity/ima/ima_kexec.c |=C2=A0 3 +++ > =C2=A03 files changed, 28 insertions(+) >=20 > diff --git a/include/linux/kexec.h b/include/linux/kexec.h > index 4dbf806bccef..bd554ced9fb2 100644 > --- a/include/linux/kexec.h > +++ b/include/linux/kexec.h > @@ -362,6 +362,9 @@ struct kimage { > =C2=A0 > =C2=A0 phys_addr_t ima_buffer_addr; > =C2=A0 size_t ima_buffer_size; > + > + unsigned long ima_segment_index; > + bool is_ima_segment_index_set; > =C2=A0#endif > =C2=A0 > =C2=A0 /* Core ELF header buffer */ > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c > index 3eedb8c226ad..606132253c79 100644 > --- a/kernel/kexec_file.c > +++ b/kernel/kexec_file.c > @@ -38,6 +38,21 @@ void set_kexec_sig_enforced(void) > =C2=A0} > =C2=A0#endif > =C2=A0 > +#ifdef CONFIG_IMA_KEXEC > +static bool check_ima_segment_index(struct kimage *image, int i) > +{ > + if (image->is_ima_segment_index_set && i =3D=3D image->ima_segment_inde= x) > + return true; > + else > + return false; > +} > +#else > +static bool check_ima_segment_index(struct kimage *image, int i) > +{ > + return false; > +} > +#endif > + > =C2=A0static int kexec_calculate_store_digests(struct kimage *image); > =C2=A0 > =C2=A0/* Maximum size in bytes for kernel/initrd files. */ > @@ -764,6 +779,13 @@ static int kexec_calculate_store_digests(struct kima= ge > *image) > =C2=A0 if (ksegment->kbuf =3D=3D pi->purgatory_buf) > =C2=A0 continue; > =C2=A0 > + /* > + * Skip the segment if ima_segment_index is set and matches > + * the current index > + */ > + if (check_ima_segment_index(image, i)) > + continue; > + > =C2=A0 ret =3D crypto_shash_update(desc, ksegment->kbuf, > =C2=A0 =C2=A0 ksegment->bufsz); > =C2=A0 if (ret) > diff --git a/security/integrity/ima/ima_kexec.c > b/security/integrity/ima/ima_kexec.c > index 89088f1fa989..704676fa6615 100644 > --- a/security/integrity/ima/ima_kexec.c > +++ b/security/integrity/ima/ima_kexec.c > @@ -160,6 +160,7 @@ void ima_add_kexec_buffer(struct kimage *image) > =C2=A0 kbuf.buffer =3D kexec_buffer; > =C2=A0 kbuf.bufsz =3D kexec_buffer_size; > =C2=A0 kbuf.memsz =3D kexec_segment_size; > + image->is_ima_segment_index_set =3D false; > =C2=A0 ret =3D kexec_add_buffer(&kbuf); > =C2=A0 if (ret) { > =C2=A0 pr_err("Error passing over kexec measurement buffer.\n"); > @@ -170,6 +171,8 @@ void ima_add_kexec_buffer(struct kimage *image) > =C2=A0 image->ima_buffer_addr =3D kbuf.mem; > =C2=A0 image->ima_buffer_size =3D kexec_segment_size; > =C2=A0 image->ima_buffer =3D kexec_buffer; > + image->ima_segment_index =3D image->nr_segments - 1; > + image->is_ima_segment_index_set =3D true; > =C2=A0 > =C2=A0 /* > =C2=A0 * kexec owns kexec_buffer after kexec_add_buffer() is called