feat(dracut): add --sbat option to add sbat policy to UKI

Take existing .sbat section from the uefi stub and merge it with vmlinux .sbat (if it exists) and user-provided .sbat parameters using the new --sbat option. For some reasons, --update-section in objcopy does not resize the .sbat section, so remove the section from the stub and add it to the UKI as new one, to avoid having incomplete SBAT strings. Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
dracutdevs · Aug 5, 2023 · fffeade · fffeade
1 parent af3076a
commit fffeade
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Showing 4 changed files with 56 additions and 2 deletions.
diff --git a/dracut.sh b/dracut.sh
@@ -272,6 +272,10 @@ Creates initial ramdisk images for preloading modules
                         Use [FILE] as a splash image when creating an UEFI
                          executable. Requires bitmap (.bmp) image format.
   --kernel-image [FILE] Location of the kernel image.
+  --sbat [PARAMETERS]   The SBAT parameters to be added to .sbat.
+                         The string "sbat,1,SBAT Version,sbat,1,
+                         https://github.com/rhboot/shim/blob/main/SBAT.md" is
+                         already added by default.
   --regenerate-all      Regenerate all initramfs images at the default location
                          for the kernel versions found on the system.
   -p, --parallel        Use parallel processing if possible (currently only
@@ -463,6 +467,7 @@ rearrange_params() {
             --long uefi-stub: \
             --long uefi-splash-image: \
             --long kernel-image: \
+            --long sbat: \
             --long no-hostonly-i18n \
             --long hostonly-i18n \
             --long hostonly-nics: \
@@ -840,6 +845,11 @@ while :; do
             PARMS_TO_STORE+=" '$2'"
             shift
             ;;
+        --sbat)
+            sbat_l="$2"
+            PARMS_TO_STORE+=" '$2'"
+            shift
+            ;;
         --no-machineid)
             machine_id_l="no"
             ;;
@@ -1079,6 +1089,7 @@ drivers_dir="${drivers_dir%"${drivers_dir##*[!/]}"}"
 [[ $uefi_stub_l ]] && uefi_stub="$uefi_stub_l"
 [[ $uefi_splash_image_l ]] && uefi_splash_image="$uefi_splash_image_l"
 [[ $kernel_image_l ]] && kernel_image="$kernel_image_l"
+[[ $sbat_l ]] && sbat="$sbat_l"
 [[ $machine_id_l ]] && machine_id="$machine_id_l"
 
 if ! [[ $outfile ]]; then
@@ -2452,6 +2463,24 @@ fi
 
 umask 077
 
+SBAT_DEFAULT="sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md"
+sbat_out=$uefi_outdir/uki.sbat
+
+clean_sbat_string() {
+    local inp=$1
+    local temp=$uefi_outdir/temp.sbat
+    sed "/${SBAT_DEFAULT//\//\\/}/d" "$inp" > "$temp"
+    [[ -s $temp ]] && cat "$temp" >> "$sbat_out"
+    rm "$temp"
+}
+
+get_sbat_string() {
+    local inp=$1
+    local out=$uefi_outdir/$2
+    objcopy -O binary --only-section=.sbat "$inp" "$out"
+    clean_sbat_string "$out"
+}
+
 if [[ $uefi == yes ]]; then
     if [[ $kernel_cmdline ]]; then
         echo -n "$kernel_cmdline" > "$uefi_outdir/cmdline.txt"
@@ -2506,6 +2535,16 @@ if [[ $uefi == yes ]]; then
         unset uefi_splash_image
     fi
 
+    echo "$SBAT_DEFAULT" > "$sbat_out"
+    if [[ -n $sbat ]]; then
+        echo "$sbat" | sed "/${SBAT_DEFAULT//\//\\/}/d" >> "$sbat_out"
+    fi
+    get_sbat_string "$kernel_image" kernel.sbat
+    get_sbat_string "$uefi_stub" stub.sbat
+
+    uefi_sbat_offs="${offs}"
+    offs=$((offs + $(stat -Lc%s "$sbat_out")))
+    offs=$((offs + "$align" - offs % "$align"))
     uefi_linux_offs="${offs}"
     offs=$((offs + $(stat -Lc%s "$kernel_image")))
     offs=$((offs + "$align" - offs % "$align"))
@@ -2517,14 +2556,19 @@ if [[ $uefi == yes ]]; then
         exit 1
     fi
 
+    tmp_uefi_stub=$uefi_outdir/elf.stub
+    cp "$uefi_stub" "$tmp_uefi_stub"
+    objcopy --remove-section .sbat "$tmp_uefi_stub" &> /dev/null
+
     if objcopy \
         ${uefi_osrelease:+--add-section .osrel="$uefi_osrelease" --change-section-vma .osrel=$(printf 0x%x "$uefi_osrelease_offs")} \
         ${uefi_cmdline:+--add-section .cmdline="$uefi_cmdline" --change-section-vma .cmdline=$(printf 0x%x "$uefi_cmdline_offs")} \
         ${uefi_splash_image:+--add-section .splash="$uefi_splash_image" --change-section-vma .splash=$(printf 0x%x "$uefi_splash_offs")} \
+        --add-section .sbat="$sbat_out" --change-section-vma .sbat="$(printf 0x%x "$uefi_sbat_offs")" \
         --add-section .linux="$kernel_image" --change-section-vma .linux="$(printf 0x%x "$uefi_linux_offs")" \
         --add-section .initrd="${DRACUT_TMPDIR}/initramfs.img" --change-section-vma .initrd="$(printf 0x%x "$uefi_initrd_offs")" \
         --image-base="$(printf 0x%x "$base_image")" \
-        "$uefi_stub" "${uefi_outdir}/linux.efi"; then
+        "$tmp_uefi_stub" "${uefi_outdir}/linux.efi"; then
         if [[ -n ${uefi_secureboot_key} && -n ${uefi_secureboot_cert} ]]; then
             if sbsign \
                 ${uefi_secureboot_engine:+--engine "$uefi_secureboot_engine"} \

diff --git a/man/dracut.8.asc b/man/dracut.8.asc
@@ -600,6 +600,11 @@ and no /etc/cmdline/*.conf will be generated into the initramfs.
     default is _/lib/modules/<KERNEL-VERSION>/vmlinuz_ or
     _/boot/vmlinuz-<KERNEL-VERSION>_.
 
+**--sbat <parameters>**::
+    Specifies the SBAT parameters, which to include in the UEFI executable. By default
+    the default SBAT string added is "sbat,1,SBAT Version,sbat,1,
+    https://github.com/rhboot/shim/blob/main/SBAT.md".
+
 **--enhanced-cpio**::
     Attempt to use the dracut-cpio binary, which optimizes archive creation for
     copy-on-write filesystems by using the copy_file_range(2) syscall via Rust's

diff --git a/man/dracut.conf.5.asc b/man/dracut.conf.5.asc
@@ -302,6 +302,11 @@ Logging levels:
     default is _/lib/modules/<KERNEL-VERSION>/vmlinuz_ or
     _/boot/vmlinuz-<KERNEL-VERSION>_.
 
+*sbat=*"__parameters__"::
+    Specifies the SBAT parameters, which to include in the UEFI executable. By default
+    the default SBAT string added is "sbat,1,SBAT Version,sbat,1,
+    https://github.com/rhboot/shim/blob/main/SBAT.md".
+
 *enhanced_cpio=*"__{yes|no}__"::
     Attempt to use the dracut-cpio binary, which optimizes archive creation for
     copy-on-write filesystems (default=no).

diff --git a/shell-completion/bash/dracut b/shell-completion/bash/dracut
@@ -46,7 +46,7 @@ _dracut() {
             --kernel-cmdline --sshkey --persistent-policy --install-optional
             --loginstall --uefi-stub --kernel-image --squash-compressor
             --sysroot --hostonly-mode --hostonly-nics --include --logfile
-            --uefi-splash-image
+            --uefi-splash-image --sbat
             '
     )