init: Add support for zstd compressed kernel

- Add the zstd and zstd22 cmds to scripts/Makefile.lib

- Add the HAVE_KERNEL_ZSTD and KERNEL_ZSTD options

Architecture specific support is still needed for decompression.

Signed-off-by: Nick Terrell <terrelln@fb.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200730190841.2071656-4-nickrterrell@gmail.com

diff --git a/Makefile b/Makefile
index 229e67f..565084f 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -464,6 +464,7 @@ KLZOP               = lzop
 LZMA           = lzma
 LZ4            = lz4c
 XZ             = xz
+ZSTD           = zstd
 
 CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
                  -Wbitwise -Wno-return-void -Wno-unknown-attribute $(CF)
@@ -512,7 +513,7 @@ CLANG_FLAGS :=
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE LEX YACC AWK INSTALLKERNEL
 export PERL PYTHON PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
-export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ
+export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD
 export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS

diff --git a/init/Kconfig b/init/Kconfig
index 0498af5..2b6409f 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -191,13 +191,16 @@ config HAVE_KERNEL_LZO
 config HAVE_KERNEL_LZ4
        bool
 
+config HAVE_KERNEL_ZSTD
+       bool
+
 config HAVE_KERNEL_UNCOMPRESSED
        bool
 
 choice
        prompt "Kernel compression mode"
        default KERNEL_GZIP
-       depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_UNCOMPRESSED
+       depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_ZSTD || HAVE_KERNEL_UNCOMPRESSED
        help
          The linux kernel is a kind of self-extracting executable.
          Several compression algorithms are available, which differ
@@ -276,6 +279,16 @@ config KERNEL_LZ4
          is about 8% bigger than LZO. But the decompression speed is
          faster than LZO.
 
+config KERNEL_ZSTD
+       bool "ZSTD"
+       depends on HAVE_KERNEL_ZSTD
+       help
+         ZSTD is a compression algorithm targeting intermediate compression
+         with fast decompression speed. It will compress better than GZIP and
+         decompress around the same speed as LZO, but slower than LZ4. You
+         will need at least 192 KB RAM or more for booting. The zstd command
+         line tool is required for compression.
+
 config KERNEL_UNCOMPRESSED
        bool "None"
        depends on HAVE_KERNEL_UNCOMPRESSED

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 916b2f7..54f7b7e 100644 (file)
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -413,6 +413,28 @@ quiet_cmd_xzkern = XZKERN  $@
 quiet_cmd_xzmisc = XZMISC  $@
       cmd_xzmisc = cat $(real-prereqs) | $(XZ) --check=crc32 --lzma2=dict=1MiB > $@
 
+# ZSTD
+# ---------------------------------------------------------------------------
+# Appends the uncompressed size of the data using size_append. The .zst
+# format has the size information available at the beginning of the file too,
+# but it's in a more complex format and it's good to avoid changing the part
+# of the boot code that reads the uncompressed size.
+#
+# Note that the bytes added by size_append will make the zstd tool think that
+# the file is corrupt. This is expected.
+#
+# zstd uses a maximum window size of 8 MB. zstd22 uses a maximum window size of
+# 128 MB. zstd22 is used for kernel compression because it is decompressed in a
+# single pass, so zstd doesn't need to allocate a window buffer. When streaming
+# decompression is used, like initramfs decompression, zstd22 should likely not
+# be used because it would require zstd to allocate a 128 MB buffer.
+
+quiet_cmd_zstd = ZSTD    $@
+      cmd_zstd = { cat $(real-prereqs) | $(ZSTD) -19; $(size_append); } > $@
+
+quiet_cmd_zstd22 = ZSTD22  $@
+      cmd_zstd22 = { cat $(real-prereqs) | $(ZSTD) -22 --ultra; $(size_append); } > $@
+
 # ASM offsets
 # ---------------------------------------------------------------------------