[PATCH v8 3/7] init: add support for zstd compressed kernel

Nick Terrell
2020-07-23T19:30:39Z

From: Nick Terrell <terrelln@fb.com>

* Adds the zstd and zstd22 cmds to scripts/Makefile.lib
* Adds the HAVE_KERNEL_ZSTD and KERNEL_ZSTD options

Architecture specific support is still needed for decompression.

Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Nick Terrell <terrelln@fb.com>
---
Makefile | 3 ++-
init/Kconfig | 15 ++++++++++++++-
scripts/Makefile.lib | 22 ++++++++++++++++++++++
3 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index fe0164a654c7..d14f9b7038ba 100644
--- 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 0498af567f70..8d99f0c5e240 100644
--- 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 tools 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 916b2f7f7098..54f7b7eb580b 100644
--- 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
# ---------------------------------------------------------------------------

--
2.27.0