From 3adf063bac2f17e5216a0312165aeb0a91af4a94 Mon Sep 17 00:00:00 2001 From: Tom Lendacky Date: Wed, 22 Feb 2023 10:39:39 -0600 Subject: [PATCH] virt/sev-guest: Return -EIO if certificate buffer is not large enough commit dd093fb08e8f8a958fec4eef36f9f09eac047f60 upstream. Commit 47894e0fa6a5 ("virt/sev-guest: Prevent IV reuse in the SNP guest driver") changed the behavior associated with the return value when the caller does not supply a large enough certificate buffer. Prior to the commit a value of -EIO was returned. Now, 0 is returned. This breaks the established ABI with the user. Change the code to detect the buffer size error and return -EIO. Fixes: 47894e0fa6a5 ("virt/sev-guest: Prevent IV reuse in the SNP guest driver") Reported-by: Larry Dewey Signed-off-by: Tom Lendacky Signed-off-by: Borislav Petkov (AMD) Tested-by: Larry Dewey Cc: Link: https://lore.kernel.org/r/2afbcae6daf13f7ad5a4296692e0a0fe1bc1e4ee.1677083979.git.thomas.lendacky@amd.com Signed-off-by: Greg Kroah-Hartman --- drivers/virt/coco/sev-guest/sev-guest.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c index 99d6062afe72..6de888bce1bb 100644 --- a/drivers/virt/coco/sev-guest/sev-guest.c +++ b/drivers/virt/coco/sev-guest/sev-guest.c @@ -379,9 +379,26 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in snp_dev->input.data_npages = certs_npages; } + /* + * Increment the message sequence number. There is no harm in doing + * this now because decryption uses the value stored in the response + * structure and any failure will wipe the VMPCK, preventing further + * use anyway. + */ + snp_inc_msg_seqno(snp_dev); + if (fw_err) *fw_err = err; + /* + * If an extended guest request was issued and the supplied certificate + * buffer was not large enough, a standard guest request was issued to + * prevent IV reuse. If the standard request was successful, return -EIO + * back to the caller as would have originally been returned. + */ + if (!rc && err == SNP_GUEST_REQ_INVALID_LEN) + return -EIO; + if (rc) { dev_alert(snp_dev->dev, "Detected error from ASP request. rc: %d, fw_err: %llu\n", @@ -397,9 +414,6 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in goto disable_vmpck; } - /* Increment to new message sequence after payload decryption was successful. */ - snp_inc_msg_seqno(snp_dev); - return 0; disable_vmpck: