From: Hans-Jörg Höxer <hshoexer@genua.de>
Subject: Re: [EXT] Re: AMD SEV: confidential autoconf whitelist
To: <tech@openbsd.org>
Date: Sat, 2 Aug 2025 22:41:33 +0200

Hi,

based on some hackroom discussion with mlarkin this diff takes a
different approach:  Add a cfdrivers flag to white list devices when
running virtualized with SEV enabled.

The filtering is now happening in config_search() isascan().

Any thoughts on that?

HJ.

-----------------------------------------------------------------------
commit f66e1eb92c59aec93ec5c44c0d3cfe8a1f4049c8
Author: Hans-Joerg Hoexer <hshoexer@genua.de>
Date:   Sat Aug 2 12:58:50 2025 +0200

    SEV: Whitelist devices in cfdrive for use when SEV is enabled
    
    Skip devices, that are not flagged for use with SEV.  Hook into
    config_search() and isascan().

diff --git a/sys/arch/amd64/amd64/bios.c b/sys/arch/amd64/amd64/bios.c
index 3a264d09d5b..73653f13703 100644
--- a/sys/arch/amd64/amd64/bios.c
+++ b/sys/arch/amd64/amd64/bios.c
@@ -50,7 +50,7 @@ const struct cfattach bios_ca = {
 };
 
 struct cfdriver bios_cd = {
-	NULL, "bios", DV_DULL
+	NULL, "bios", DV_DULL, CD_SEVVM
 };
 
 struct smbios_entry smbios_entry;
diff --git a/sys/arch/amd64/amd64/cpu.c b/sys/arch/amd64/amd64/cpu.c
index 1287c610344..c7d7fb9101f 100644
--- a/sys/arch/amd64/amd64/cpu.c
+++ b/sys/arch/amd64/amd64/cpu.c
@@ -445,7 +445,7 @@ const struct cfattach cpu_ca = {
 };
 
 struct cfdriver cpu_cd = {
-	NULL, "cpu", DV_DULL
+	NULL, "cpu", DV_DULL, CD_SEVVM
 };
 
 /*
diff --git a/sys/arch/amd64/amd64/ioapic.c b/sys/arch/amd64/amd64/ioapic.c
index 9989fdfeb29..6286ab708c3 100644
--- a/sys/arch/amd64/amd64/ioapic.c
+++ b/sys/arch/amd64/amd64/ioapic.c
@@ -231,7 +231,7 @@ const struct cfattach ioapic_ca = {
 };
 
 struct cfdriver ioapic_cd = {
-	NULL, "ioapic", DV_DULL
+	NULL, "ioapic", DV_DULL, CD_SEVVM
 };
 
 int
diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index 991dd2cbeb6..e9f42af31df 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -1474,6 +1474,8 @@ init_x86_64(paddr_t first_avail)
 		cpu_init_early_vctrap(first_avail);
 		first_avail += 2 * NBPG;
 	}
+	if (ISSET(cpu_sev_guestmode, SEV_STAT_ENABLED))
+		boothowto |= RB_SEVVM;
 
 	/*
 	 * locore0 mapped 3 pages for use before the pmap is initialized
diff --git a/sys/arch/amd64/amd64/mainbus.c b/sys/arch/amd64/amd64/mainbus.c
index ebc86e3767b..28a5c018c3d 100644
--- a/sys/arch/amd64/amd64/mainbus.c
+++ b/sys/arch/amd64/amd64/mainbus.c
@@ -83,7 +83,7 @@ const struct cfattach mainbus_ca = {
 };
 
 struct cfdriver mainbus_cd = {
-	NULL, "mainbus", DV_DULL
+	NULL, "mainbus", DV_DULL, CD_SEVVM
 };
 
 int	mainbus_print(void *, const char *);
diff --git a/sys/dev/acpi/acpi.c b/sys/dev/acpi/acpi.c
index 7bcf56cab49..2a33b7b0029 100644
--- a/sys/dev/acpi/acpi.c
+++ b/sys/dev/acpi/acpi.c
@@ -184,7 +184,7 @@ struct acpi_softc *acpi_softc;
 extern struct aml_node aml_root;
 
 struct cfdriver acpi_cd = {
-	NULL, "acpi", DV_DULL
+	NULL, "acpi", DV_DULL, CD_SEVVM
 };
 
 uint8_t
diff --git a/sys/dev/acpi/acpimadt.c b/sys/dev/acpi/acpimadt.c
index 3faed32b355..2539ec68139 100644
--- a/sys/dev/acpi/acpimadt.c
+++ b/sys/dev/acpi/acpimadt.c
@@ -48,7 +48,7 @@ const struct cfattach acpimadt_ca = {
 };
 
 struct cfdriver acpimadt_cd = {
-	NULL, "acpimadt", DV_DULL
+	NULL, "acpimadt", DV_DULL, CD_SEVVM
 };
 
 int acpimadt_validate(struct acpi_madt *);
diff --git a/sys/dev/ic/com.c b/sys/dev/ic/com.c
index dd45e3c901c..7eace6f06f0 100644
--- a/sys/dev/ic/com.c
+++ b/sys/dev/ic/com.c
@@ -96,7 +96,7 @@ void	compwroff(struct com_softc *);
 void	cominit(bus_space_tag_t, bus_space_handle_t, int, int);
 
 struct cfdriver com_cd = {
-	NULL, "com", DV_TTY
+	NULL, "com", DV_TTY, CD_SEVVM
 };
 
 int	comdefaultrate = TTYDEF_SPEED;
diff --git a/sys/dev/isa/isa.c b/sys/dev/isa/isa.c
index 2d11dc33a84..9837c3a11b0 100644
--- a/sys/dev/isa/isa.c
+++ b/sys/dev/isa/isa.c
@@ -62,6 +62,7 @@
 #include <sys/malloc.h>
 #include <sys/device.h>
 #include <sys/extent.h>
+#include <sys/reboot.h>
 
 #include <dev/isa/isareg.h>
 #include <dev/isa/isavar.h>
@@ -84,7 +85,7 @@ const struct cfattach isa_ca = {
 };
 
 struct cfdriver isa_cd = {
-	NULL, "isa", DV_DULL, CD_INDIRECT
+	NULL, "isa", DV_DULL, CD_INDIRECT | CD_SEVVM
 };
 
 int
@@ -218,6 +219,10 @@ isascan(struct device *parent, void *match)
 	ia.ipa_ndrq = 2;
 	ia.ia_delaybah = sc->sc_delaybah;
 
+	if (ISSET(boothowto, RB_SEVVM) &&
+	    !ISSET(cf->cf_driver->cd_mode, CD_SEVVM))
+		return;
+
 	if (cf->cf_fstate == FSTATE_STAR) {
 		struct isa_attach_args ia2 = ia;
 
diff --git a/sys/dev/pci/pci.c b/sys/dev/pci/pci.c
index c0376842914..c2b713a6728 100644
--- a/sys/dev/pci/pci.c
+++ b/sys/dev/pci/pci.c
@@ -90,7 +90,7 @@ const struct cfattach pci_ca = {
 };
 
 struct cfdriver pci_cd = {
-	NULL, "pci", DV_DULL
+	NULL, "pci", DV_DULL, CD_SEVVM
 };
 
 int	pci_ndomains;
diff --git a/sys/dev/pci/ppb.c b/sys/dev/pci/ppb.c
index cf7cb120cc1..9439ca07aee 100644
--- a/sys/dev/pci/ppb.c
+++ b/sys/dev/pci/ppb.c
@@ -113,7 +113,7 @@ const struct cfattach ppb_ca = {
 };
 
 struct cfdriver ppb_cd = {
-	NULL, "ppb", DV_DULL
+	NULL, "ppb", DV_DULL, CD_SEVVM
 };
 
 void	ppb_alloc_busrange(struct ppb_softc *, struct pci_attach_args *,
diff --git a/sys/dev/pv/if_vio.c b/sys/dev/pv/if_vio.c
index a94945a8ea0..7ea483c6e40 100644
--- a/sys/dev/pv/if_vio.c
+++ b/sys/dev/pv/if_vio.c
@@ -382,7 +382,7 @@ const struct cfattach vio_ca = {
 };
 
 struct cfdriver vio_cd = {
-	NULL, "vio", DV_IFNET
+	NULL, "vio", DV_IFNET, CD_SEVVM
 };
 
 int
diff --git a/sys/dev/pv/pvbus.c b/sys/dev/pv/pvbus.c
index 165fcc9fbff..c4761a318e3 100644
--- a/sys/dev/pv/pvbus.c
+++ b/sys/dev/pv/pvbus.c
@@ -68,7 +68,8 @@ const struct cfattach pvbus_ca = {
 struct cfdriver pvbus_cd = {
 	NULL,
 	"pvbus",
-	DV_DULL
+	DV_DULL,
+	CD_SEVVM
 };
 
 struct pvbus_type {
diff --git a/sys/dev/pv/pvclock.c b/sys/dev/pv/pvclock.c
index 89eff0ce248..0e82226583c 100644
--- a/sys/dev/pv/pvclock.c
+++ b/sys/dev/pv/pvclock.c
@@ -125,7 +125,8 @@ const struct cfattach pvclock_ca = {
 struct cfdriver pvclock_cd = {
 	NULL,
 	"pvclock",
-	DV_DULL
+	DV_DULL,
+	CD_SEVVM
 };
 
 struct timecounter pvclock_timecounter = {
diff --git a/sys/dev/pv/vioblk.c b/sys/dev/pv/vioblk.c
index 7f7a518332f..a6c4462a37e 100644
--- a/sys/dev/pv/vioblk.c
+++ b/sys/dev/pv/vioblk.c
@@ -146,7 +146,7 @@ const struct cfattach vioblk_ca = {
 };
 
 struct cfdriver vioblk_cd = {
-	NULL, "vioblk", DV_DULL
+	NULL, "vioblk", DV_DULL, CD_SEVVM
 };
 
 const struct scsi_adapter vioblk_switch = {
diff --git a/sys/dev/pv/viornd.c b/sys/dev/pv/viornd.c
index 484f7ce1be0..5e1fa06b8d5 100644
--- a/sys/dev/pv/viornd.c
+++ b/sys/dev/pv/viornd.c
@@ -66,7 +66,7 @@ const struct cfattach viornd_ca = {
 };
 
 struct cfdriver viornd_cd = {
-	NULL, "viornd", DV_DULL
+	NULL, "viornd", DV_DULL, CD_SEVVM
 };
 
 int
diff --git a/sys/dev/pv/virtio.c b/sys/dev/pv/virtio.c
index ac0432dc9f9..4a32c960908 100644
--- a/sys/dev/pv/virtio.c
+++ b/sys/dev/pv/virtio.c
@@ -48,7 +48,7 @@ void		 vq_free_entry(struct virtqueue *, struct vq_entry *);
 struct vq_entry	*vq_alloc_entry(struct virtqueue *);
 
 struct cfdriver virtio_cd = {
-	NULL, "virtio", DV_DULL
+	NULL, "virtio", DV_DULL, CD_SEVVM
 };
 
 static const char * const virtio_device_name[] = {
diff --git a/sys/dev/pv/vmmci.c b/sys/dev/pv/vmmci.c
index 984626393cd..14b66502675 100644
--- a/sys/dev/pv/vmmci.c
+++ b/sys/dev/pv/vmmci.c
@@ -72,7 +72,7 @@ const struct cfattach vmmci_ca = {
 #define VMMCI_F_SYNCRTC		(1ULL<<2)
 
 struct cfdriver vmmci_cd = {
-	NULL, "vmmci", DV_DULL
+	NULL, "vmmci", DV_DULL, CD_SEVVM
 };
 
 int
diff --git a/sys/dev/softraid.c b/sys/dev/softraid.c
index c10ebeaaa93..0c1e184074c 100644
--- a/sys/dev/softraid.c
+++ b/sys/dev/softraid.c
@@ -88,7 +88,7 @@ const struct cfattach softraid_ca = {
 };
 
 struct cfdriver softraid_cd = {
-	NULL, "softraid", DV_DULL
+	NULL, "softraid", DV_DULL, CD_SEVVM
 };
 
 /* scsi & discipline */
diff --git a/sys/dev/vscsi.c b/sys/dev/vscsi.c
index 31885a6b9c9..b7687877e13 100644
--- a/sys/dev/vscsi.c
+++ b/sys/dev/vscsi.c
@@ -89,7 +89,8 @@ const struct cfattach vscsi_ca = {
 struct cfdriver vscsi_cd = {
 	NULL,
 	"vscsi",
-	DV_DULL
+	DV_DULL,
+	CD_SEVVM
 };
 
 void		vscsi_cmd(struct scsi_xfer *);
diff --git a/sys/kern/subr_autoconf.c b/sys/kern/subr_autoconf.c
index 41633140dc6..787ff869382 100644
--- a/sys/kern/subr_autoconf.c
+++ b/sys/kern/subr_autoconf.c
@@ -216,6 +216,9 @@ config_search(cfmatch_t fn, struct device *parent, void *aux)
 			if (cf->cf_driver->cd_class == DV_TAPE)
 				continue;
 		}
+		if (ISSET(boothowto, RB_SEVVM) &&
+		    !ISSET(cf->cf_driver->cd_mode, CD_SEVVM))
+			continue;
 		for (p = cf->cf_parents; *p >= 0; p++)
 			if (parent->dv_cfdata == &cfdata[*p])
 				mapply(&m, cf);
diff --git a/sys/scsi/mpath.c b/sys/scsi/mpath.c
index c94a4ff5cf7..cf41e8f6aa5 100644
--- a/sys/scsi/mpath.c
+++ b/sys/scsi/mpath.c
@@ -79,7 +79,8 @@ const struct cfattach mpath_ca = {
 struct cfdriver mpath_cd = {
 	NULL,
 	"mpath",
-	DV_DULL
+	DV_DULL,
+	CD_SEVVM
 };
 
 void		mpath_cmd(struct scsi_xfer *);
diff --git a/sys/scsi/scsiconf.c b/sys/scsi/scsiconf.c
index 495020a23a3..db154f0d634 100644
--- a/sys/scsi/scsiconf.c
+++ b/sys/scsi/scsiconf.c
@@ -102,7 +102,7 @@ const struct cfattach scsibus_ca = {
 };
 
 struct cfdriver scsibus_cd = {
-	NULL, "scsibus", DV_DULL
+	NULL, "scsibus", DV_DULL, CD_SEVVM
 };
 
 struct scsi_quirk_inquiry_pattern {
diff --git a/sys/scsi/sd.c b/sys/scsi/sd.c
index 9b02314c679..e564d6c3f8b 100644
--- a/sys/scsi/sd.c
+++ b/sys/scsi/sd.c
@@ -116,7 +116,7 @@ const struct cfattach sd_ca = {
 };
 
 struct cfdriver sd_cd = {
-	NULL, "sd", DV_DISK
+	NULL, "sd", DV_DISK, CD_SEVVM
 };
 
 const struct scsi_inquiry_pattern sd_patterns[] = {
diff --git a/sys/sys/device.h b/sys/sys/device.h
index 5dccec16cf8..ace259f085a 100644
--- a/sys/sys/device.h
+++ b/sys/sys/device.h
@@ -139,6 +139,7 @@ struct cfattach {
 /* For cd_mode, below */
 #define CD_INDIRECT		1
 #define CD_SKIPHIBERNATE	2
+#define CD_SEVVM		4
 
 struct cfdriver {
 	void	**cd_devs;		/* devices found */
diff --git a/sys/sys/reboot.h b/sys/sys/reboot.h
index bf3e7f82680..70e987dc194 100644
--- a/sys/sys/reboot.h
+++ b/sys/sys/reboot.h
@@ -59,6 +59,7 @@
 #define	RB_RESET	0x08000	/* just reset, no cleanup  */
 #define	RB_GOODRANDOM	0x10000	/* excellent random seed loaded */
 #define	RB_UNHIBERNATE	0x20000	/* unhibernate */
+#define RB_SEVVM	0x40000	/* VM booting with SEV enabled */
 
 /*
  * Constants for converting boot-style device number to type,