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Fri, 07 Nov 2025 04:31:42 -0500 X-MC-Unique: kc5534LfMnGD2FHOmi4G9A-1 X-Mimecast-MFC-AGG-ID: kc5534LfMnGD2FHOmi4G9A_1762507901 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 717D619560B5; Fri, 7 Nov 2025 09:31:39 +0000 (UTC) Received: from localhost (unknown [10.72.112.190]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AE3161800346; Fri, 7 Nov 2025 09:31:37 +0000 (UTC) Date: Fri, 7 Nov 2025 17:31:32 +0800 From: Baoquan He To: Pingfan Liu Cc: kexec@lists.infradead.org, linux-integrity@vger.kernel.org, Andrew Morton , Mimi Zohar , Roberto Sassu , Alexander Graf , Steven Chen , stable@vger.kernel.org Subject: Re: [PATCHv2 2/2] kernel/kexec: Fix IMA when allocation happens in CMA area Message-ID: References: <20251106065904.10772-1-piliu@redhat.com> <20251106065904.10772-2-piliu@redhat.com> Precedence: bulk X-Mailing-List: linux-integrity@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On 11/07/25 at 05:00pm, Pingfan Liu wrote: > On Fri, Nov 07, 2025 at 01:25:41PM +0800, Baoquan He wrote: > > On 11/07/25 at 01:13pm, Pingfan Liu wrote: > > > On Fri, Nov 7, 2025 at 9:51 AM Baoquan He wrote: > > > > > > > > On 11/06/25 at 06:01pm, Pingfan Liu wrote: > > > > > On Thu, Nov 6, 2025 at 4:01 PM Baoquan He wrote: > > > > > > > > > > > > On 11/06/25 at 02:59pm, Pingfan Liu wrote: > > > > > > > When I tested kexec with the latest kernel, I ran into the following warning: > > > > > > > > > > > > > > [ 40.712410] ------------[ cut here ]------------ > > > > > > > [ 40.712576] WARNING: CPU: 2 PID: 1562 at kernel/kexec_core.c:1001 kimage_map_segment+0x144/0x198 > > > > > > > [...] > > > > > > > [ 40.816047] Call trace: > > > > > > > [ 40.818498] kimage_map_segment+0x144/0x198 (P) > > > > > > > [ 40.823221] ima_kexec_post_load+0x58/0xc0 > > > > > > > [ 40.827246] __do_sys_kexec_file_load+0x29c/0x368 > > > > > > > [...] > > > > > > > [ 40.855423] ---[ end trace 0000000000000000 ]--- > > > > > > > > > > > > > > This is caused by the fact that kexec allocates the destination directly > > > > > > > in the CMA area. In that case, the CMA kernel address should be exported > > > > > > > directly to the IMA component, instead of using the vmalloc'd address. > > > > > > > > > > > > Well, you didn't update the log accordingly. > > > > > > > > > > > > > > > > I am not sure what you mean. Do you mean the earlier content which I > > > > > replied to you? > > > > > > > > No. In v1, you return cma directly. But in v2, you return its direct > > > > mapping address, isnt' it? > > > > > > > > > > Yes. But I think it is a fault in the code, which does not convey the > > > expression in the commit log. Do you think I should rephrase the words > > > "the CMA kernel address" as "the CMA kernel direct mapping address"? > > > > That's fine to me. > > > > > > > > > > > > > > > > Do you know why cma area can't be mapped into vmalloc? > > > > > > > > > > > Should not the kernel direct mapping be used? > > > > > > > > When image->segment_cma[i] has value, image->ima_buffer_addr also > > > > contains the physical address of the cma area, why cma physical address > > > > can't be mapped into vmalloc and cause the failure and call trace? > > > > > > > > > > It could be done using the vmalloc approach, but it's unnecessary. > > > IIUC, kimage_map_segment() was introduced to provide a contiguous > > > virtual address for IMA access, since the IND_SRC pages are scattered > > > throughout the kernel. However, in the CMA case, there is already a > > > contiguous virtual address in the kernel direct mapping range. > > > Normally, when we have a physical address, we simply use > > > phys_to_virt() to get its corresponding kernel virtual address. > > > > OK, I understand cma area is contiguous, and no need to map into > > vmalloc. I am wondering why in the old code mapping cma addrss into > > vmalloc cause the warning which you said is a IMA problem. > > > > It doesn't go that far. The old code doesn't map CMA into vmalloc'd > area. > > void *kimage_map_segment(struct kimage *image, int idx) > { > ... > for_each_kimage_entry(image, ptr, entry) { > if (entry & IND_DESTINATION) { > dest_page_addr = entry & PAGE_MASK; > } else if (entry & IND_SOURCE) { > if (dest_page_addr >= addr && dest_page_addr < eaddr) { > src_page_addr = entry & PAGE_MASK; > src_pages[i++] = > virt_to_page(__va(src_page_addr)); > if (i == npages) > break; > dest_page_addr += PAGE_SIZE; > } > } > } > > /* Sanity check. */ > WARN_ON(i < npages); //--> This is the warning thrown by kernel > > vaddr = vmap(src_pages, npages, VM_MAP, PAGE_KERNEL); > kfree(src_pages); > > if (!vaddr) > pr_err("Could not map ima buffer.\n"); > > return vaddr; > } > > When CMA is used, there is no IND_SOURCE, so we have i=0 < npages. > Now, I see how my words ("In that case, the CMA kernel address should be > exported directly to the IMA component, instead of using the vmalloc'd > address.") confused you. As for "instead of using the vmalloc'd > address", I meant to mention "vmap()" approach. Ok, I got it. It's truly a bug because if image->segment_cma[idx] is valid, the current kimage_map_segment() can't collect the source pages at all since they are not marked with IND_DESTINATION|IND_SOURCE as normal segment does. In that situation, we can take the direct mapping address of image->segment_cma[idx] which is more efficient, instead of collecting source pages and vmap().