Re: [RFC PATCH 01/17] x86/boot: Check boot param's cc_blob_address for direct boot mode

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On 11/10/2022 7:39 AM, Michael Roth wrote:
-	 * bp->cc_blob_address should only be set by boot/compressed kernel.
-	 * Initialize it to 0 to ensure that uninitialized values from
-	 * buggy bootloaders aren't propagated.
+	 * bp->cc_blob_address should only be set by boot/compressed
+	 * kernel and hypervisor with direct boot mode. Initialize it
+	 * to 0 after checking in order to ensure that uninitialized
+	 * values from buggy bootloaders aren't propagated.
  	 */
-	if (bp)
-		bp->cc_blob_address = 0;
+	if (bp) {
+		cc_info = (struct cc_blob_sev_info *)(unsigned long)
+			bp->cc_blob_address;
+
+		if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
+			bp->cc_blob_address = 0;
It doesn't seem great to rely on SEV_HDR_MAGIC to determine whether
bp->cc_blob_address is valid or not since it is only a 32-bit value.

Would it be possible to use a setup_data entry of type SETUP_CC_BLOB
in bp->hdr.setup_data instead? There's already handling for that in
find_cc_blob_setup_data() so it should "just work".

Hi Michael:
Thanks for your review. I will have a try. Hypervisor may set cc_blob_address directly and so propose this.







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