stand: set st_dev/st_ino in the loader's ZFS stat for veriexec

The loader's ZFS implementation never set st_dev or st_ino in
zfs_dnode_stat(). With an uninitialized struct stat, veriexec's device
comparison in lib/libsecureboot/veopen.c read stack garbage and skipped
the matching manifest entry, failing with a spurious "no entry" on ZFS
root under UEFI Secure Boot.

Rather than zeroing the device (which would break veriexec's ability to
tell apart the same path on different datasets), populate st_dev and
st_ino with the same intrinsic identifiers the kernel uses:

- st_dev = the dataset's ds_fsid_guid (as the kernel does via
  dmu_objset_fsid_guid()/dsl_dataset_fsid_guid()), already read in
  zfs_mount_dataset() and now propagated through struct zfsmount.
- st_ino = the object number resolved in zfs_lookup(), propagated
  through struct file (the loader's equivalent of the kernel's z_id).

dev_t and ino_t are 64-bit on FreeBSD, so both are assigned directly
with no hashing. A memset() at the top of zfs_dnode_stat() zeroes the
remaining fields so they no longer hold stack garbage.

Tested on 16.0-CURRENT (amd64), ZFS-on-GELI root: rebuilt and re-signed
the EFI loader; the system boots under UEFI Secure Boot with
mac_veriexec active.

(boot1 segment was modified by kevans)

PR:		295935
Sponsored by:	Defenso

Reviewed-by: kevans
Pull-Request: https://github.com/freebsd/freebsd-src/pull/2271
(cherry picked from commit b567434a592e1a35b20c5a39c4ccc2ea9e00601d)

3 files changed, 56 insertions, 11 deletions

diff --git a/stand/efi/boot1/zfs_module.c b/stand/efi/boot1/zfs_module.c
index 16722b33f0b9..261753a7acfe 100644
--- a/stand/efi/boot1/zfs_module.c
+++ b/stand/efi/boot1/zfs_module.c
@@ -205,7 +205,7 @@ load(const char *filepath, dev_info_t *devinfo, void **bufp, size_t *bufsize)
 		return (EFI_NOT_FOUND);
 	}
 
-	if ((err = zfs_lookup(&zmount, filepath, &dn)) != 0) {
+	if ((err = zfs_lookup(&zmount, filepath, &dn, NULL)) != 0) {
 		if (err == ENOENT) {
 			DPRINTF("Failed to find '%s' on pool '%s' (%d)\n",
 			    filepath, spa->spa_name, err);
@@ -216,7 +216,8 @@ load(const char *filepath, dev_info_t *devinfo, void **bufp, size_t *bufsize)
 		return (EFI_INVALID_PARAMETER);
 	}
 
-	if ((err = zfs_dnode_stat(spa, &dn, &st)) != 0) {
+	/* Only st_size is inspected here, so identity is irrelevant. */
+	if ((err = zfs_dnode_stat(spa, &dn, &st, 0, 0)) != 0) {
 		printf("Failed to stat '%s' on pool '%s' (%d)\n", filepath,
 		    spa->spa_name, err);
 		return (EFI_INVALID_PARAMETER);
diff --git a/stand/libsa/zfs/zfs.c b/stand/libsa/zfs/zfs.c
index 70a102f6425d..2784c0afd412 100644
--- a/stand/libsa/zfs/zfs.c
+++ b/stand/libsa/zfs/zfs.c
@@ -85,6 +85,7 @@ struct fs_ops zfs_fsops = {
 struct file {
 	off_t		f_seekp;	/* seek pointer */
 	dnode_phys_t	f_dnode;
+	uint64_t	f_objnum;	/* object number (st_ino) */
 	uint64_t	f_zap_type;	/* zap type for readdir */
 	uint64_t	f_num_leafs;	/* number of fzap leaf blocks */
 	zap_leaf_phys_t	*f_zap_leaf;	/* zap leaf buffer */
@@ -120,7 +121,7 @@ zfs_open(const char *upath, struct open_file *f)
 		return (ENOMEM);
 	f->f_fsdata = fp;
 
-	rc = zfs_lookup(mount, upath, &fp->f_dnode);
+	rc = zfs_lookup(mount, upath, &fp->f_dnode, &fp->f_objnum);
 	fp->f_seekp = 0;
 	if (rc) {
 		f->f_fsdata = NULL;
@@ -214,10 +215,11 @@ static int
 zfs_stat(struct open_file *f, struct stat *sb)
 {
 	struct devdesc *dev = f->f_devdata;
-	const spa_t *spa = ((struct zfsmount *)dev->d_opendata)->spa;
+	struct zfsmount *zm = dev->d_opendata;
 	struct file *fp = (struct file *)f->f_fsdata;
 
-	return (zfs_dnode_stat(spa, &fp->f_dnode, sb));
+	return (zfs_dnode_stat(zm->spa, &fp->f_dnode, sb, zm->fsid_guid,
+	    fp->f_objnum));
 }
 
 static int
diff --git a/stand/libsa/zfs/zfsimpl.c b/stand/libsa/zfs/zfsimpl.c
index e5920004bd9d..b6d14090fc76 100644
--- a/stand/libsa/zfs/zfsimpl.c
+++ b/stand/libsa/zfs/zfsimpl.c
@@ -48,6 +48,7 @@ struct zfsmount {
 	const spa_t		*spa;
 	objset_phys_t		objset;
 	uint64_t		rootobj;
+	uint64_t		fsid_guid;	/* mount's ds_fsid_guid */
 	STAILQ_ENTRY(zfsmount)	next;
 };
 
@@ -3433,7 +3434,8 @@ done:
  * and return its details in *objset
  */
 static int
-zfs_mount_dataset(const spa_t *spa, uint64_t objnum, objset_phys_t *objset)
+zfs_mount_dataset(const spa_t *spa, uint64_t objnum, objset_phys_t *objset,
+    uint64_t *fsid_guid)
 {
 	dnode_phys_t dataset;
 	dsl_dataset_phys_t *ds;
@@ -3450,6 +3452,17 @@ zfs_mount_dataset(const spa_t *spa, uint64_t objnum, objset_phys_t *objset)
 		return (EIO);
 	}
 
+	/*
+	 * Capture the dataset's intrinsic on-disk identifier so callers can
+	 * expose it as st_dev (matches the kernel, which derives the fsid from
+	 * dmu_objset_fsid_guid()/ds_fsid_guid).  ds_fsid_guid is a 56-bit ID
+	 * that may change to avoid collisions; ds_guid is a never-changing
+	 * 64-bit ID and would be the alternative if absolute stability over
+	 * time were required -- to be decided in review.
+	 */
+	if (fsid_guid != NULL)
+		*fsid_guid = ds->ds_fsid_guid;
+
 	return (0);
 }
 
@@ -3518,7 +3531,8 @@ zfs_mount_impl(const spa_t *spa, uint64_t rootobj, struct zfsmount *mount)
 		return (EIO);
 	}
 
-	if (zfs_mount_dataset(spa, rootobj, &mount->objset)) {
+	if (zfs_mount_dataset(spa, rootobj, &mount->objset,
+	    &mount->fsid_guid)) {
 		printf("ZFS: can't open root filesystem\n");
 		return (EIO);
 	}
@@ -3703,9 +3717,17 @@ zfs_spa_init(spa_t *spa)
 }
 
 static int
-zfs_dnode_stat(const spa_t *spa, dnode_phys_t *dn, struct stat *sb)
+zfs_dnode_stat(const spa_t *spa, dnode_phys_t *dn, struct stat *sb,
+    uint64_t fsid_guid, uint64_t objnum)
 {
 
+	/*
+	 * Zero the whole struct first so fields this function does not fill
+	 * (st_nlink, timestamps, st_blocks, ...) hold 0 rather than stack
+	 * garbage.  st_dev/st_ino are then overwritten with real values below.
+	 */
+	memset(sb, 0, sizeof(*sb));
+
 	if (dn->dn_bonustype != DMU_OT_SA) {
 		znode_phys_t *zp = (znode_phys_t *)dn->dn_bonus;
 
@@ -3754,6 +3776,15 @@ zfs_dnode_stat(const spa_t *spa, dnode_phys_t *dn, struct stat *sb)
 		free(buf);
 	}
 
+	/*
+	 * Populate the identity fields used by veriexec to tell apart the same
+	 * path on different datasets/filesystems.  dev_t and ino_t are 64-bit
+	 * on FreeBSD, so the dataset GUID and object number fit directly with
+	 * no hashing or truncation.
+	 */
+	sb->st_dev = (dev_t)fsid_guid;
+	sb->st_ino = (ino_t)objnum;
+
 	return (0);
 }
 
@@ -3818,7 +3849,8 @@ struct obj_list {
  * Lookup a file and return its dnode.
  */
 static int
-zfs_lookup(const struct zfsmount *mount, const char *upath, dnode_phys_t *dnode)
+zfs_lookup(const struct zfsmount *mount, const char *upath,
+    dnode_phys_t *dnode, uint64_t *objnum_out)
 {
 	int rc;
 	uint64_t objnum;
@@ -3904,7 +3936,8 @@ zfs_lookup(const struct zfsmount *mount, const char *upath, dnode_phys_t *dnode)
 		element[q - p] = 0;
 		p = q;
 
-		if ((rc = zfs_dnode_stat(spa, &dn, &sb)) != 0)
+		/* Only st_mode is inspected here, so identity is irrelevant. */
+		if ((rc = zfs_dnode_stat(spa, &dn, &sb, 0, 0)) != 0)
 			goto done;
 		if (!S_ISDIR(sb.st_mode)) {
 			rc = ENOTDIR;
@@ -3929,7 +3962,8 @@ zfs_lookup(const struct zfsmount *mount, const char *upath, dnode_phys_t *dnode)
 		/*
 		 * Check for symlink.
 		 */
-		rc = zfs_dnode_stat(spa, &dn, &sb);
+		/* Only st_mode is inspected here, so identity is irrelevant. */
+		rc = zfs_dnode_stat(spa, &dn, &sb, 0, 0);
 		if (rc)
 			goto done;
 		if (S_ISLNK(sb.st_mode)) {
@@ -3976,6 +4010,14 @@ zfs_lookup(const struct zfsmount *mount, const char *upath, dnode_phys_t *dnode)
 	}
 
 	*dnode = dn;
+	/*
+	 * objnum tracks the object number of the dnode we just resolved (the
+	 * loader's equivalent of the kernel's z_id/db_object); hand it back so
+	 * the file can expose it as st_ino.  Callers that do not need it pass
+	 * NULL.
+	 */
+	if (objnum_out != NULL)
+		*objnum_out = objnum;
 done:
 	STAILQ_FOREACH_SAFE(entry, &on_cache, entry, tentry)
 		free(entry);