roms: only support SeaBIOS/SeaGRUB on x86

Never, ever build images where GRUB is the primary payload.

These options have been removed from target.cfg handling:

* seabios_withgrub
* grub_withseabios

The "payload_grub" variable now does the same thing as
the old "seabios_withgrub" variable, if set.

The "grubonly" configuration is retained, and enabled by
default when SeaGRUB is enabled (non-grubonly also available).

Due to lbmk issue #216, it is no longer Libreboot policy to
make GRUB the primary payload on any board. GRUB's sheer size
and complexity, plus the large number of memory corruption issues
similar to it that *have* been fixed over the years, tells me
that GRUB is a liability when it is the primary payload.

SeaBIOS is a much safer payload to run as primary, on x86, due
to its smaller size and much more conservative development; it
is simply far less likely to break.

If GRUB breaks in the future, the user's machine is not
bricked. This is because SeaBIOS is the default payload.

Since I no longer wish to ever provide GRUB as a primary
payload, supporting it in lbmk adds needless bloat that
will later probably break anyway due to lack of testing,
so let's just assume SeaGRUB in all cases where the user
wants to use a GRUB payload.

You can mitigate potential security issues with SeaBIOS
by disabling option ROM execution, which can be done at
runtime by inserting integers into CBFS. The SeaBIOS
documentation says how to do this.

Libreboot's GRUB hardening guide still says how to add
a bootorder file in CBFS, making SeaBIOS only load GRUB
from CBFS, and nothing else. This, combined with the
disablement of option ROM execution (if using Intel
graphics), pretty much provides the same security benefits
as GRUB-as-primary, for example when setting a GRUB password
and GPG checks, with encrypted /boot as in the hardening guide.

Signed-off-by: Leah Rowe <leah@libreboot.org>

1 files changed, 30 insertions, 57 deletions

diff --git a/script/roms b/script/roms
index 213f1b1f..92f79db4 100755
--- a/script/roms
+++ b/script/roms
@@ -22,10 +22,9 @@ stm32dir="$stm32src/boards"
 
 # Disable all payloads by default.
 # target.cfg files have to specifically enable [a] payload(s)
-pv="payload_uboot payload_grub_withseabios payload_seabios payload_memtest t"
-pv="$pv payload_seabios_withgrub payload_grub"
+pv="payload_uboot payload_seabios payload_memtest t payload_grub"
 v="romdir cbrom initmode displaymode cbcfg targetdir tree release ubootelf"
-v="$v grub_timeout board grub_scan_disk uboot_config grubtree grubelf tmpmv"
+v="$v board grub_scan_disk uboot_config grubtree grubelf tmpmv"
 eval `setvars "n" $pv`
 eval `setvars "" $v boards targets serdir ser`
 
@@ -97,30 +96,24 @@ configure_target()
 	# Override the above defaults using target.cfg
 	eval `setcfg "$targetdir/target.cfg"`
 
+	[ -z "$tree" ] && $err "$board: tree not defined"
+	[ "$xbmk_release" = "y" ] && [ "$release" = "n" ] && return 1
+	[ "$board" = "$tree" ] && return 1
+
+	[ -n "$uboot_config" ] || uboot_config="default"
+	[ "$payload_uboot" = "y" ] || payload_seabios="y"
+	[ "$payload_grub" = "y" ] && payload_seabios="y"
+	[ "$payload_seabios" = "y" ] && [ -n "$payload_uboot" = "y" ] && \
+	    $err "$board: U-Boot and SeaBIOS/GRUB are both enabled."
+
 	[ -z "$grub_scan_disk" ] && grub_scan_disk="nvme ahci ata"
 
 	[ -n "$grubtree" ] || grubtree="default"
 	grubelf="elf/grub/$grubtree/payload/grub.elf"
 
-	[ -z "$tree" ] && $err "$board: tree not defined"
-
-	[ "$payload_memtest" != "y" ] && payload_memtest="n"
+	[ "$payload_memtest" = "y" ] || payload_memtest="n"
 	[ "$(uname -m)" = "x86_64" ] || payload_memtest="n"
-
-	[ "$payload_grub_withseabios" = "y" ] && eval `setvars "y" \
-	    payload_grub payload_seabios payload_seabios_withgrub`
-	[ "$payload_seabios_withgrub" = "y" ] && payload_seabios="y"
-
-	# The reverse logic must not be applied. If SeaBIOS-with-GRUB works,
-	# that doesn't mean GRUB-with-SeaBIOS will, e.g. VGA ROM execution
-	[ "$payload_grub" != "y" ] && [ "$payload_seabios" != "y" ] && \
-	    [ "$payload_uboot" != "y" ] && $err "'$board' defines no payload"
-
-	[ "$payload_uboot" = "y" ] || payload_uboot="n"
-	[ -n "$uboot_config" ] || uboot_config="default"
-
-	[ "$xbmk_release" = "y" ] && [ "$release" = "n" ] && return 1
-	[ "$board" = "$tree" ] && return 1; return 0
+	[ "$payload_uboot" = "y" ] && payload_memtest="n"; return 0
 }
 
 build_payloads()
@@ -134,11 +127,7 @@ build_payloads()
 	[ -f "$cbfstool" ] || x_ ./update trees -b coreboot utils $tree
 	[ "$payload_memtest" = "y" ] && x_ ./update trees -b memtest86plus
 	[ "$payload_seabios" = "y" ] && x_ ./update trees -b seabios
-
-	if [ "$payload_grub" = "y" ] || [ "$payload_seabios_withgrub" = "y" ]
-	then
-		[ -f "$grubelf" ] || x_ ./update trees -b grub $grubtree
-	fi
+	[ "$payload_grub" = "y" ] && x_ ./update trees -b grub $grubtree
 
 	[ "$payload_uboot" = "y" ] || return 0
 	x_ ./update trees -b u-boot $board
@@ -181,19 +170,18 @@ build_roms()
 	[ "$payload_memtest" != "y" ] || cbfs "$cbrom" \
 	    "elf/memtest86plus/memtest.bin" img/memtest
 	[ "$payload_seabios" = "y" ] && build_seabios_roms
-	[ "$payload_grub" != "y" ] || build_grub_roms "$cbrom" "grub"
 	[ "$payload_uboot" = "y" ] && x_ cp "$_cbrom" "$cbrom" && \
 	    build_uboot_roms; return 0
 }
 
 build_seabios_roms()
 {
-	if [ "$payload_seabios_withgrub" = "y" ]; then
+	if [ "$payload_grub" = "y" ]; then # SeaBIOS with GRUB
 		t="$(mktemp -t coreboot_rom.XXXXXXXXXX)"
 		x_ cp "$cbrom" "$t"
-		build_grub_roms "$t" "seabios_withgrub"
-	else
-		t="$(mkSeabiosRom "$cbrom" "fallback/payload")" || \
+		build_seagrub_roms "$t" "seabios_withgrub"
+	else # SeaBIOS only
+		t="$(mkSeabiosRom "$cbrom")" || \
 		    $err "build_seabios_roms: cannot build tmprom"
 		newrom="$romdir/seabios_${board}_${initmode}_$displaymode"
 		[ "$initmode" = "normal" ] && newrom="$romdir/seabios" \
@@ -203,40 +191,25 @@ build_seabios_roms()
 	x_ rm -f "$t"
 }
 
-# Make separate ROM images with GRUB payload
-build_grub_roms()
+build_seagrub_roms()
 {
-	tmprom="$1"
-	payload1="$2" # allow values: grub, seabios, seabios_withgrub
-
-	grub_cbfs="fallback/payload"
-	if [ "$payload1" = "grub" ] && [ "$payload_grub_withseabios" = "y" ]
-	then
-		tmpmv="$(mkSeabiosRom "$tmprom" "seabios.elf")" || \
-		    $err "build_grub_roms 1 $board: can't build tmprom"
-	elif [ "$payload1" != "grub" ] && [ "$payload_seabios_withgrub" = "y" ]
-	then
-		grub_cbfs="img/grub2"
-		tmpmv="$(mkSeabiosRom "$tmprom" fallback/payload)" || \
-		    $err "build_grub_roms 2 $board: can't build tmprom"
-	fi
-	[ -n "$tmpmv" ] && [ -f "$tmpmv" ] && x_ mv "$tmpmv" "$tmprom"
+	tmpmv="$(mkSeabiosRom "$1")" || $err "$board: !mk grub tmprom"
+	x_ mv "$tmpmv" "$1"
 
 	# we only need insert grub.elf once, for each coreboot config:
-	cbfs "$tmprom" "$grubelf" "$grub_cbfs"
+	cbfs "$1" "$grubelf" "img/grub2"
 
 	printf "set grub_scan_disk=\"%s\"\n" "$grub_scan_disk" \
 	    > "$tmpdir/tmpcfg" || $err "set grub_scan_disk, $grub_scan_disk"
-	cbfs "$tmprom" "$tmpdir/tmpcfg" scan.cfg raw
+	cbfs "$1" "$tmpdir/tmpcfg" scan.cfg raw
 
-	newrom="$romdir/${payload1}_${board}_${initmode}_$displaymode.rom"
-	[ "$initmode" = "normal" ] && newrom="$romdir/${payload1}_" \
+	newrom="$romdir/seabios_withgrub_${board}_${initmode}_$displaymode.rom"
+	[ "$initmode" = "normal" ] && newrom="$romdir/seabios_withgrub_" \
 	    && newrom="$newrom${board}_$initmode.rom"
-	cprom cp "$tmprom" "$newrom"
+	cprom cp "$1" "$newrom"
 
-	[ "$payload1" = "grub" ] && return 0
-	cbfs "$tmprom" "$grubdata/bootorder" bootorder raw
-	cprom cp "$tmprom" "${newrom%.rom}_grubfirst.rom"
+	cbfs "$1" "$grubdata/bootorder" bootorder raw # SeaGRUB
+	cprom cp "$1" "${newrom%.rom}_grubfirst.rom"
 }
 
 # make a rom in /tmp/ and then print the path of that ROM
@@ -245,7 +218,7 @@ mkSeabiosRom() {
 	_seabioself="elf/seabios/default/$initmode/bios.bin.elf"
 
 	x_ cp "$1" "$tmprom"
-	cbfs "$tmprom" "$_seabioself" "$2"
+	cbfs "$tmprom" "$_seabioself" "fallback/payload"
 	x_ "$cbfstool" "$tmprom" add-int -i 3000 -n etc/ps2-keyboard-spinup
 
 	z="2"; [ "$initmode" = "vgarom" ] && z="0"