Re: [PATCH v2 1/2] lib: add support for ZSTD-compressed kernel

From: Kees Cook
Date: Tue Mar 17 2020 - 17:02:42 EST

On Mon, Mar 16, 2020 at 03:30:16PM +0100, Petr Malat wrote:
> Add support for extracting ZSTD-compressed kernel images, as well as
> ZSTD-compressed initramfs.
>
> ZSTD compression ratio is roughly 10% worst than xz, but the
> decompression is 10x faster. Currently, this is one of the optimal
> algorithms available in the kernel, as there isn't an algorithm,
> which would provide a better compression ratio and a shorter
> decompression time.

It might be worth splitting this patch into 2 pieces: one to extract the
logic (which is most of the patch and the description), and then a
separate one to add the initrd support (since that touches logically
separate things like a new Makefile cmd, etc etc). That patch
description could talk about requiring the "zstd" command line tool,
etc. (Which should likely be mentioned in the Kconfig description too.

More notes below...

>
> Signed-off-by: Petr Malat <oss@xxxxxxxxx>
> ---
> include/linux/decompress/unzstd.h | 12 +++
> init/Kconfig | 15 ++-
> lib/Kconfig | 4 +
> lib/Makefile | 1 +
> lib/decompress.c | 5 +
> lib/decompress_unzstd.c | 159 ++++++++++++++++++++++++++++++
> lib/zstd/decompress.c | 2 +
> lib/zstd/fse_decompress.c | 4 +-
> scripts/Makefile.lib | 3 +
> usr/Kconfig | 24 +++++
> 10 files changed, 227 insertions(+), 2 deletions(-)
> create mode 100644 include/linux/decompress/unzstd.h
> create mode 100644 lib/decompress_unzstd.c
>
> diff --git a/include/linux/decompress/unzstd.h b/include/linux/decompress/unzstd.h
> new file mode 100644
> index 000000000000..dd2c49d47456
> --- /dev/null
> +++ b/include/linux/decompress/unzstd.h
> @@ -0,0 +1,12 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef DECOMPRESS_UNZSTD_H
> +#define DECOMPRESS_UNZSTD_H
> +
> +int unzstd(unsigned char *inbuf, long len,
> + long (*fill)(void*, unsigned long),
> + long (*flush)(void*, unsigned long),
> + unsigned char *output,
> + long *pos,
> + void (*error)(char *x));
> +#endif
> +
> diff --git a/init/Kconfig b/init/Kconfig
> index a34064a031a5..628eb3c290a2 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -172,13 +172,16 @@ config HAVE_KERNEL_LZO
> config HAVE_KERNEL_LZ4
> bool
>
> +config HAVE_KERNEL_ZSTD
> + bool

The HAVE_KERNEL_ZSTD changes should be put in the kernel enablement patch.

> +
> 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
> @@ -257,6 +260,16 @@ 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
> + Its compression ratio is roughly 10% worst than xz, but the
> + decompression is 10x faster. Currently, this is one of the optimal
> + algorithms available in the kernel, as there isn't an algorithm,
> + which would provide a better compression ratio and a shorter
> + decompression time.
> +
> config KERNEL_UNCOMPRESSED
> bool "None"
> depends on HAVE_KERNEL_UNCOMPRESSED
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 6e790dc55c5b..df301bd888d7 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -329,6 +329,10 @@ config DECOMPRESS_LZ4
> select LZ4_DECOMPRESS
> tristate
>
> +config DECOMPRESS_ZSTD
> + select ZSTD_DECOMPRESS
> + tristate
> +
> #
> # Generic allocator support is selected if needed
> #
> diff --git a/lib/Makefile b/lib/Makefile
> index 93217d44237f..3ab9f4c31f8b 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -158,6 +158,7 @@ lib-$(CONFIG_DECOMPRESS_LZMA) += decompress_unlzma.o
> lib-$(CONFIG_DECOMPRESS_XZ) += decompress_unxz.o
> lib-$(CONFIG_DECOMPRESS_LZO) += decompress_unlzo.o
> lib-$(CONFIG_DECOMPRESS_LZ4) += decompress_unlz4.o
> +lib-$(CONFIG_DECOMPRESS_ZSTD) += decompress_unzstd.o
>
> obj-$(CONFIG_TEXTSEARCH) += textsearch.o
> obj-$(CONFIG_TEXTSEARCH_KMP) += ts_kmp.o
> diff --git a/lib/decompress.c b/lib/decompress.c
> index 857ab1af1ef3..ab3fc90ffc64 100644
> --- a/lib/decompress.c
> +++ b/lib/decompress.c
> @@ -13,6 +13,7 @@
> #include <linux/decompress/inflate.h>
> #include <linux/decompress/unlzo.h>
> #include <linux/decompress/unlz4.h>
> +#include <linux/decompress/unzstd.h>
>
> #include <linux/types.h>
> #include <linux/string.h>
> @@ -37,6 +38,9 @@
> #ifndef CONFIG_DECOMPRESS_LZ4
> # define unlz4 NULL
> #endif
> +#ifndef CONFIG_DECOMPRESS_ZSTD
> +# define unzstd NULL
> +#endif
>
> struct compress_format {
> unsigned char magic[2];
> @@ -52,6 +56,7 @@ static const struct compress_format compressed_formats[] __initconst = {
> { {0xfd, 0x37}, "xz", unxz },
> { {0x89, 0x4c}, "lzo", unlzo },
> { {0x02, 0x21}, "lz4", unlz4 },
> + { {0x28, 0xb5}, "zstd", unzstd },
> { {0, 0}, NULL, NULL }
> };
>
> diff --git a/lib/decompress_unzstd.c b/lib/decompress_unzstd.c
> new file mode 100644
> index 000000000000..b8be89250033
> --- /dev/null
> +++ b/lib/decompress_unzstd.c
> @@ -0,0 +1,159 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Wrapper for decompressing ZSTD-compressed kernel, initramfs, and initrd
> + * Based on decompress_unlz4.c
> + *
> + * Copyright (C) 2020, Petr Malat <oss@xxxxxxxxx>
> + */
> +
> +#ifdef STATIC
> +#define PREBOOT

Can you please namespace PREBOOT (as done for other decompressors),
as maybe ZSTD_PREBOOT?

> +#include "zstd/zstd_internal.h"
> +#include "zstd/huf_decompress.c"
> +#include "zstd/entropy_common.c"
> +#include "zstd/fse_decompress.c"
> +#include "zstd/zstd_common.c"
> +#include "zstd/decompress.c"
> +#include "xxhash.c"
> +#else
> +#include <linux/decompress/unzstd.h>
> +#include <linux/zstd.h>
> +#endif
> +#include <linux/types.h>
> +#include <linux/decompress/mm.h>
> +#include <linux/compiler.h>
> +
> +STATIC inline int INIT unzstd(u8 *input, long in_len,
> + long (*fill)(void *, unsigned long),
> + long (*flush)(void *, unsigned long),
> + u8 *output, long *posp,
> + void (*error)(char *x))
> +{
> + int ret = -1, ws = 1 << ZSTD_WINDOWLOG_MAX;
> + u8 *inp, *outp;
> + ZSTD_DStream *zstd;
> + void *workspace;
> + size_t workspace_size;
> + ZSTD_outBuffer out;
> + ZSTD_inBuffer in;
> + unsigned long out_len;
> + unsigned long pos;
> +
> + if (output) {
> + out_len = ULONG_MAX; // Caller knows data will fit
> + outp = output;
> + } else if (!flush) {
> + error("NULL output pointer and no flush function provided");
> + goto exit_0;
> + } else {
> + out_len = ZSTD_DStreamOutSize();
> + outp = large_malloc(out_len);
> + if (!outp) {
> + error("Could not allocate output buffer");
> + goto exit_0;
> + }
> + }
> +
> + if (input && fill) {
> + error("Both input pointer and fill function provided,");
> + goto exit_1;
> + } else if (input) {
> + ZSTD_frameParams p;
> +
> + inp = input;
> + if (!ZSTD_getFrameParams(&p, input, in_len))
> + ws = p.windowSize;
> + } else if (!fill) {
> + error("NULL input pointer and missing fill function");
> + goto exit_1;
> + } else {
> + in_len = ZSTD_DStreamInSize();
> + inp = large_malloc(in_len);
> + if (!inp) {
> + error("Could not allocate input buffer");
> + goto exit_1;
> + }
> + }
> +
> + workspace_size = ZSTD_DStreamWorkspaceBound(ws);
> + workspace = large_malloc(workspace_size);
> + if (!workspace) {
> + error("Could not allocate workspace");
> + goto exit_2;
> + }
> +
> + zstd = ZSTD_initDStream(ws, workspace, workspace_size);
> + if (!zstd) {
> + error("Could not initialize ZSTD");
> + goto exit_3;
> + }
> +
> + in.src = inp;
> + in.size = in_len;
> + in.pos = 0;
> + if (posp)
> + *posp = 0;
> +
> + for (;;) {
> + if (fill) {
> + in.size = fill(inp, in_len);
> + if (in.size == 0)
> + break;
> + } else if (in.size == in.pos) {
> + break;
> + }
> +init: out.dst = outp;
> + out.size = out_len;
> + out.pos = 0;
> + pos = in.pos;
> +
> + ret = ZSTD_decompressStream(zstd, &out, &in);
> + if (posp)
> + *posp += in.pos - pos;
> + if (ZSTD_isError(ret)) {
> + error("Decompression failed");
> + ret = -EIO;
> + goto exit_3;
> + }
> +
> + if (flush && out.pos) {
> + if (flush(out.dst, out.pos) != out.pos) {
> + ret = -EIO;
> + goto exit_3;
> + }
> + goto init;
> + }
> +
> + if (ret == 0) {
> + ret = ZSTD_resetDStream(zstd);
> + if (ZSTD_isError(ret)) {
> + ret = -EIO;
> + goto exit_3;
> + }
> + }
> + if (in.pos < in.size)
> + goto init;
> + }
> +
> + ret = 0;
> +
> +exit_3: large_free(workspace);
> +exit_2: if (!input)
> + large_free(inp);
> +exit_1: if (!output)
> + large_free(outp);
> +exit_0: return ret;
> +}
> +
> +#ifdef PREBOOT
> +STATIC int INIT __decompress(unsigned char *buf, long in_len,
> + long (*fill)(void*, unsigned long),
> + long (*flush)(void*, unsigned long),
> + unsigned char *output, long out_len,
> + long *posp,
> + void (*error)(char *x)
> + )
> +{
> + return unzstd(buf, in_len, fill, flush, output, posp, error);
> +}
> +#endif
> diff --git a/lib/zstd/decompress.c b/lib/zstd/decompress.c
> index 269ee9a796c1..6a5e1ce22719 100644
> --- a/lib/zstd/decompress.c
> +++ b/lib/zstd/decompress.c
> @@ -42,9 +42,11 @@
> /*-*************************************
> * Macros
> ***************************************/
> +#ifndef PREBOOT
> #define ZSTD_isError ERR_isError /* for inlining */
> #define FSE_isError ERR_isError
> #define HUF_isError ERR_isError
> +#endif
>
> /*_*******************************************************
> * Memory operations
> diff --git a/lib/zstd/fse_decompress.c b/lib/zstd/fse_decompress.c
> index a84300e5a013..bd4e9c891d96 100644
> --- a/lib/zstd/fse_decompress.c
> +++ b/lib/zstd/fse_decompress.c
> @@ -54,12 +54,13 @@
> /* **************************************************************
> * Error Management
> ****************************************************************/
> -#define FSE_isError ERR_isError
> #define FSE_STATIC_ASSERT(c) \
> { \
> enum { FSE_static_assert = 1 / (int)(!!(c)) }; \
> } /* use only *after* variable declarations */
>
> +#ifndef PREBOOT
> +#define FSE_isError ERR_isError
> /* check and forward error code */
> #define CHECK_F(f) \
> { \
> @@ -67,6 +68,7 @@
> if (FSE_isError(e)) \
> return e; \
> }
> +#endif
>
> /* **************************************************************
> * Templates
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 3fa32f83b2d7..1c2f2dc528dc 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -337,6 +337,9 @@ quiet_cmd_lz4 = LZ4 $@
> cmd_lz4 = { cat $(real-prereqs) | lz4c -l -c1 stdin stdout; \
> $(size_append); } > $@
>
> +quiet_cmd_zstd = ZSTD $@
> + cmd_zstd = { cat $(real-prereqs) | zstd -19 --zstd=wlog=21; $(size_append); } > $@
> +
> # U-Boot mkimage
> # ---------------------------------------------------------------------------
>
> diff --git a/usr/Kconfig b/usr/Kconfig
> index a6b68503d177..892eb15957db 100644
> --- a/usr/Kconfig
> +++ b/usr/Kconfig
> @@ -106,6 +106,15 @@ config RD_LZ4
> Support loading of a LZ4 encoded initial ramdisk or cpio buffer
> If unsure, say N.
>
> +config RD_ZSTD
> + bool "Support initial ramdisk/ramfs compressed using ZSTD"
> + default y
> + depends on BLK_DEV_INITRD
> + select DECOMPRESS_ZSTD
> + help
> + Support loading of a ZSTD encoded initial ramdisk or cpio buffer
> + If unsure, say N.
> +
> choice
> prompt "Built-in initramfs compression mode"
> depends on INITRAMFS_SOURCE!=""
> @@ -214,6 +223,19 @@ config INITRAMFS_COMPRESSION_LZ4
> If you choose this, keep in mind that most distros don't provide lz4
> by default which could cause a build failure.
>
> +config INITRAMFS_COMPRESSION_ZSTD
> + bool "ZSTD"
> + depends on RD_ZSTD
> + help
> + Its compression ratio is roughly 10% worst than xz, but the
> + decompression is 10x faster. Currently, this is one of the optimal
> + algorithms available in the kernel, as there isn't an algorithm,
> + which would provide a better compression ratio and a shorter
> + decompression time.
> +
> + If you choose this, keep in mind that you may need to install the zstd
> + tool to be able to compress the initram.
> +
> endchoice
>
> config INITRAMFS_COMPRESSION
> @@ -226,10 +248,12 @@ config INITRAMFS_COMPRESSION
> default ".xz" if INITRAMFS_COMPRESSION_XZ
> default ".lzo" if INITRAMFS_COMPRESSION_LZO
> default ".lz4" if INITRAMFS_COMPRESSION_LZ4
> + default ".zst" if INITRAMFS_COMPRESSION_ZSTD
> default ".gz" if RD_GZIP
> default ".lz4" if RD_LZ4
> default ".lzo" if RD_LZO
> default ".xz" if RD_XZ
> default ".lzma" if RD_LZMA
> default ".bz2" if RD_BZIP2
> + default ".zst" if RD_ZSTD
> default ""
> --
> 2.20.1
>

The rest looks good (though as mentioned, I think splitting this from
initrd enablement makes sense).

--
Kees Cook