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Wed, 05 Mar 2025 07:37:24 -0500 X-MC-Unique: ibpPt9VsO-iXHgqmpj8QAg-1 X-Mimecast-MFC-AGG-ID: ibpPt9VsO-iXHgqmpj8QAg_1741178242 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 77EDD19560A2; Wed, 5 Mar 2025 12:37:21 +0000 (UTC) Received: from localhost (unknown [10.72.112.32]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 46AD2193EFD8; Wed, 5 Mar 2025 12:37:18 +0000 (UTC) Date: Wed, 5 Mar 2025 20:37:13 +0800 From: Baoquan He To: steven chen Cc: zohar@linux.ibm.com, 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, madvenka@linux.microsoft.com, nramas@linux.microsoft.com, James.Bottomley@hansenpartnership.com, vgoyal@redhat.com, dyoung@redhat.com Subject: Re: [PATCH v9 3/7] ima: kexec: skip IMA segment validation after kexec soft reboot Message-ID: References: <20250304190351.96975-1-chenste@linux.microsoft.com> <20250304190351.96975-4-chenste@linux.microsoft.com> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250304190351.96975-4-chenste@linux.microsoft.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On 03/04/25 at 11:03am, steven chen wrote: > The kexec_calculate_store_digests() function calculates and stores the > digest of the segment during the kexec_file_load syscall, where the > IMA segment is also allocated. > > With this series, the IMA segment will be updated with the measurement > log at the kexec execute stage when a soft reboot is initiated. > Therefore, the digests should be updated for the IMA segment in the > normal case. > > The content of memory segments carried over to the new kernel during the > kexec systemcall can be changed at kexec 'execute' stage, but the size > and the location of the memory segments cannot be changed at kexec > 'execute' stage. > > However, during the kexec execute stage, if kexec_calculate_store_digests() > API is call to update the digest, it does not reuse the same memory segment ~ called > allocated during the kexec 'load' stage and the new memory segment required > cannot be transferred/mapped to the new kernel. > > As a result, digest verification will fail in verify_sha256_digest() > after a kexec soft reboot into the new kernel. Therefore, the digest > calculation/verification of the IMA segment needs to be skipped. > > To address this, skip the calculation and storage of the digest for the > IMA segment in kexec_calculate_store_digests() so that it is not added > to the purgatory_sha_regions. > > Since verify_sha256_digest() only verifies 'purgatory_sha_regions', > no change is needed in verify_sha256_digest() in this context. > > With this change, the IMA segment is not included in the digest > calculation, storage, and verification. > > Signed-off-by: Tushar Sugandhi > Cc: Eric Biederman > Cc: Baoquan He > Cc: Vivek Goyal > Cc: Dave Young > Signed-off-by: steven chen > Reviewed-by: Stefan Berger > Reviewed-by: Mimi Zohar > --- > include/linux/kexec.h | 3 +++ > kernel/kexec_file.c | 22 ++++++++++++++++++++++ > security/integrity/ima/ima_kexec.c | 3 +++ > 3 files changed, 28 insertions(+) Other than the nit, LGTM. > > diff --git a/include/linux/kexec.h b/include/linux/kexec.h > index 7d6b12f8b8d0..107e726f2ef3 100644 > --- a/include/linux/kexec.h > +++ b/include/linux/kexec.h > @@ -362,6 +362,9 @@ struct kimage { > > phys_addr_t ima_buffer_addr; > size_t ima_buffer_size; > + > + unsigned long ima_segment_index; > + bool is_ima_segment_index_set; > #endif > > /* 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) > } > #endif > > +#ifdef CONFIG_IMA_KEXEC > +static bool check_ima_segment_index(struct kimage *image, int i) > +{ > + if (image->is_ima_segment_index_set && i == image->ima_segment_index) > + return true; > + else > + return false; > +} > +#else > +static bool check_ima_segment_index(struct kimage *image, int i) > +{ > + return false; > +} > +#endif > + > static int kexec_calculate_store_digests(struct kimage *image); > > /* Maximum size in bytes for kernel/initrd files. */ > @@ -764,6 +779,13 @@ static int kexec_calculate_store_digests(struct kimage *image) > if (ksegment->kbuf == pi->purgatory_buf) > continue; > > + /* > + * Skip the segment if ima_segment_index is set and matches > + * the current index > + */ > + if (check_ima_segment_index(image, i)) > + continue; > + > ret = crypto_shash_update(desc, ksegment->kbuf, > ksegment->bufsz); > if (ret) > diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c > index 6195df128482..0465beca8867 100644 > --- a/security/integrity/ima/ima_kexec.c > +++ b/security/integrity/ima/ima_kexec.c > @@ -169,6 +169,7 @@ void ima_add_kexec_buffer(struct kimage *image) > kbuf.buffer = kexec_buffer; > kbuf.bufsz = kexec_buffer_size; > kbuf.memsz = kexec_segment_size; > + image->is_ima_segment_index_set = false; > ret = kexec_add_buffer(&kbuf); > if (ret) { > pr_err("Error passing over kexec measurement buffer.\n"); > @@ -179,6 +180,8 @@ void ima_add_kexec_buffer(struct kimage *image) > image->ima_buffer_addr = kbuf.mem; > image->ima_buffer_size = kexec_segment_size; > image->ima_buffer = kexec_buffer; > + image->ima_segment_index = image->nr_segments - 1; > + image->is_ima_segment_index_set = true; > > /* > * kexec owns kexec_buffer after kexec_add_buffer() is called > -- > 2.25.1 >