From 7ffeb2fc26707f613685ce7711c26a9de5890ab1 Mon Sep 17 00:00:00 2001 From: Alexey Kardashevskiy Date: Wed, 11 Jun 2025 14:08:41 +1000 Subject: [PATCH] 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 db10cb9b5746 ("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: Alexey Kardashevskiy Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Tom Lendacky Reviewed-by: Dionna Glaze Link: https://lore.kernel.org/20250611040842.2667262-4-aik@amd.com --- arch/x86/coco/sev/core.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c index 068653865bfb..b0d423a353ab 100644 --- a/arch/x86/coco/sev/core.c +++ b/arch/x86/coco/sev/core.c @@ -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 */ -- 2.47.2