Commit 7ffeb2fc authored by Alexey Kardashevskiy's avatar Alexey Kardashevskiy Committed by Borislav Petkov (AMD)
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x86/sev: Document requirement for linear mapping of guest request buffers 



The Guest Request supports 3 types of messages now, the largest is the
extended variant of MSG_REPORT_REQ: sizeof(snp_ext_report_req)==112.  These
used to be allocated on stack and then moved to the SNP guest platform device
(snp_guest_dev) for the reason explained in

  db10cb9b ("virt: sevguest: Fix passing a stack buffer as a scatterlist target"):

aesgcm_encrypt() and aesgcm_decrypt() are used for guest messages and might
potentially use a crypto accelerator which requires DMA buffers to be in the
linear mapping.

Add a comment, warn and return an error when the buffers are not in linear
mapping.

Signed-off-by: default avatarAlexey Kardashevskiy <aik@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: default avatarDionna Glaze <dionnaglaze@google.com>
Link: https://lore.kernel.org/20250611040842.2667262-4-aik@amd.com
parent d100016e

arch/x86/coco/sev/core.c

+9 −0
Original line number Diff line number Diff line
@@ -2008,6 +2008,15 @@ int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req 
	u64 seqno;

	int rc;



	/*

	 * enc_payload() calls aesgcm_encrypt(), which can potentially offload to HW.

	 * The offload's DMA SG list of data to encrypt has to be in linear mapping.

	 */

	if (!virt_addr_valid(req->req_buf) || !virt_addr_valid(req->resp_buf)) {

		pr_warn("AES-GSM buffers must be in linear mapping");

		return -EINVAL;

	}



	guard(mutex)(&snp_cmd_mutex);



	/* Check if the VMPCK is not empty */