On Tue, Mar 17, 2020 at 05:22:59PM -0700, Nick Terrell wrote:
> * Add unzstd() and the zstd decompress interface.
> * Add zstd support to decompress_method().
>
> The decompress_method() and unzstd() functions are used to decompress
> the initramfs and the initrd. The __decompress() function is used in
> the preboot environment to decompress a zstd compressed kernel.
>
> The zstd decompression function allows the input and output buffers to
> overlap because that is used by x86 kernel decompression.
>
> Signed-off-by: Nick Terrell <terrelln@xxxxxx>
> ---
> include/linux/decompress/unzstd.h | 11 +
> lib/Kconfig | 4 +
> lib/Makefile | 1 +
> lib/decompress.c | 5 +
> lib/decompress_unzstd.c | 337 ++++++++++++++++++++++++++++++
> 5 files changed, 358 insertions(+)
> 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..56d539ae880f
> --- /dev/null
> +++ b/include/linux/decompress/unzstd.h
> @@ -0,0 +1,11 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef LINUX_DECOMPRESS_UNZSTD_H
> +#define LINUX_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_fn)(char *x));
> +#endif
> diff --git a/lib/Kconfig b/lib/Kconfig
> index bc7e56370129..11de5fa09a52 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -336,6 +336,10 @@ 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 611872c06926..09ad45ba6883 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -160,6 +160,7 @@ 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..f38eba5efe23
> --- /dev/null
> +++ b/lib/decompress_unzstd.c
> @@ -0,0 +1,337 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Important notes about in-place decompression
> + *
> + * At least on x86, the kernel is decompressed in place: the compressed data
> + * is placed to the end of the output buffer, and the decompressor overwrites
> + * most of the compressed data. There must be enough safety margin to
> + * guarantee that the write position is always behind the read position.
> + *
> + * The safety margin for ZSTD with a 128 KB block size is calculated below.
> + * Note that the margin with ZSTD is bigger than with GZIP or XZ!
> + *
> + * The worst case for in-place decompression is that the beginning of
> + * the file is compressed extremely well, and the rest of the file is
> + * uncompressible. Thus, we must look for worst-case expansion when the
> + * compressor is encoding uncompressible data.
> + *
> + * The structure of the .zst file in case of a compresed kernel is as follows.
> + * Maximum sizes (as bytes) of the fields are in parenthesis.
> + *
> + * Frame Header: (18)
> + * Blocks: (N)
> + * Checksum: (4)
> + *
> + * The frame header and checksum overhead is at most 22 bytes.
> + *
> + * ZSTD stores the data in blocks. Each block has a header whose size is
> + * a 3 bytes. After the block header, there is up to 128 KB of payload.
> + * The maximum uncompressed size of the payload is 128 KB. The minimum
> + * uncompressed size of the payload is never less than the payload size
> + * (excluding the block header).
> + *
> + * The assumption, that the uncompressed size of the payload is never
> + * smaller than the payload itself, is valid only when talking about
> + * the payload as a whole. It is possible that the payload has parts where
> + * the decompressor consumes more input than it produces output. Calculating
> + * the worst case for this would be tricky. Instead of trying to do that,
> + * let's simply make sure that the decompressor never overwrites any bytes
> + * of the payload which it is currently reading.
> + *
> + * Now we have enough information to calculate the safety margin. We need
> + * - 22 bytes for the .zst file format headers;
> + * - 3 bytes per every 128 KiB of uncompressed size (one block header per
> + * block); and
> + * - 128 KiB (biggest possible zstd block size) to make sure that the
> + * decompressor never overwrites anything from the block it is currently
> + * reading.
> + *
> + * We get the following formula:
> + *
> + * safety_margin = 22 + uncompressed_size * 3 / 131072 + 131072
> + * <= 22 + (uncompressed_size >> 15) + 131072
> + */
> +
> +#ifdef STATIC
> + /*
> + * Preboot environments #include "path/to/decompress_unzstd.c".
> + * All of the source files we depend on must be #included.
> + * zstd's only source dependeny is xxhash, which has no source
> + * dependencies.
> + *
> + * zstd and xxhash both avoid declaring themselves as modules
> + * when PREBOOT is defined.
> + */
> +# define PREBOOT
Can you use ZSTD_PREBOOT for this? Other decompressors namespace this
define.
(And a style nit: I'd put the comment above the #ifdef STATIC and use a
single space, not a tab, for the "indented" #-lines)
> +# include "xxhash.c"
> +# include "zstd/entropy_common.c"
> +# include "zstd/fse_decompress.c"
> +# include "zstd/huf_decompress.c"
> +# include "zstd/zstd_common.c"
> +# include "zstd/decompress.c"
> +#endif
> +
> +#include <linux/decompress/mm.h>
> +#include <linux/kernel.h>
> +#include <linux/zstd.h>
> +
> +/* 8 MB maximum window size */
> +#define ZSTD_WINDOWSIZE_MAX (1 << 23)
> +/* Size of the input and output buffers in multi-call mdoe */
> +#define ZSTD_IOBUF_SIZE 4096
> +
> +static int INIT handle_zstd_error(size_t ret, void (*error)(char *x))
> +{
> + const int err = ZSTD_getErrorCode(ret);
> +
> + if (!ZSTD_isError(ret))
> + return 0;
> +
> + switch (err) {
> + case ZSTD_error_memory_allocation:
> + error("ZSTD decompressor ran out of memory");
> + break;
> + case ZSTD_error_prefix_unknown:
> + error("Input is not in the ZSTD format (wrong magic bytes)");
> + break;
> + case ZSTD_error_dstSize_tooSmall:
> + case ZSTD_error_corruption_detected:
> + case ZSTD_error_checksum_wrong:
> + error("ZSTD-compressed data is corrupt");
> + break;
> + default:
> + error("ZSTD-compressed data is probably corrupt");
> + break;
> + }
> + return -1;
> +}
> +
> +/*
> + * Handle the case where we have the entire input and output in one segment.
> + * We can allocate less memory (no circular buffer for the sliding window),
> + * and avoid some memcpy() calls.
> + */
> +static int INIT decompress_single(const u8 *in_buf, long in_len, u8 *out_buf,
> + long out_len, long *in_pos,
> + void (*error)(char *x))
> +{
> + const size_t wksp_size = ZSTD_DCtxWorkspaceBound();
> + void *wksp = large_malloc(wksp_size);
> + ZSTD_DCtx *dctx = ZSTD_initDCtx(wksp, wksp_size);
> + int err;
> + size_t ret;
> +
> + if (dctx == NULL) {
> + error("Out of memory while allocating ZSTD_DCtx");
> + err = -1;
> + goto out;
> + }
> + /*
> + * Find out how large the frame actually is, there may be junk at
> + * the end of the frame that ZSTD_decompressDCtx() can't handle.
> + */
> + ret = ZSTD_findFrameCompressedSize(in_buf, in_len);
> + err = handle_zstd_error(ret, error);
> + if (err)
> + goto out;
> + in_len = (long)ret;
> +
> + ret = ZSTD_decompressDCtx(dctx, out_buf, out_len, in_buf, in_len);
> + err = handle_zstd_error(ret, error);
> + if (err)
> + goto out;
> +
> + if (in_pos != NULL)
> + *in_pos = in_len;
> +
> + err = 0;
> +out:
> + if (wksp != NULL)
> + large_free(wksp);
> + return err;
> +}
> +
> +static int INIT __unzstd(unsigned char *in_buf, long in_len,
> + long (*fill)(void*, unsigned long),
> + long (*flush)(void*, unsigned long),
> + unsigned char *out_buf, long out_len,
> + long *in_pos,
> + void (*error)(char *x))
> +{
> + ZSTD_inBuffer in;
> + ZSTD_outBuffer out;
> + ZSTD_frameParams params;
> + void *in_allocated = NULL;
> + void *out_allocated = NULL;
> + void *wksp = NULL;
> + size_t wksp_size;
> + ZSTD_DStream *dstream;
> + int err;
> + size_t ret;
> +
> + if (out_len == 0)
> + out_len = LONG_MAX; /* no limit */
> +
> + if (fill == NULL && flush == NULL)
> + /*
> + * We can decompress faster and with less memory when we have a
> + * single chunk.
> + */
> + return decompress_single(in_buf, in_len, out_buf, out_len,
> + in_pos, error);
> +
> + /*
> + * If in_buf is not provided, we must be using fill(), so allocate
> + * a large enough buffer. If it is provided, it must be at least
> + * ZSTD_IOBUF_SIZE large.
> + */
> + if (in_buf == NULL) {
> + in_allocated = malloc(ZSTD_IOBUF_SIZE);
> + if (in_allocated == NULL) {
> + error("Out of memory while allocating input buffer");
> + err = -1;
> + goto out;
> + }
> + in_buf = in_allocated;
> + in_len = 0;
> + }
> + /* Read the first chunk, since we need to decode the frame header. */
> + if (fill != NULL)
> + in_len = fill(in_buf, ZSTD_IOBUF_SIZE);
> + if (in_len < 0) {
> + error("ZSTD-compressed data is truncated");
> + err = -1;
> + goto out;
> + }
> + /* Set the first non-empty input buffer. */
> + in.src = in_buf;
> + in.pos = 0;
> + in.size = in_len;
> + /* Allocate the output buffer if we are using flush(). */
> + if (flush != NULL) {
> + out_allocated = malloc(ZSTD_IOBUF_SIZE);
> + if (out_allocated == NULL) {
> + error("Out of memory while allocating output buffer");
> + err = -1;
> + goto out;
> + }
> + out_buf = out_allocated;
> + out_len = ZSTD_IOBUF_SIZE;
> + }
> + /* Set the output buffer. */
> + out.dst = out_buf;
> + out.pos = 0;
> + out.size = out_len;
> +
> + /*
> + * We need to know the window size to allocate the ZSTD_DStream.
> + * Since we are streaming, we need to allocate a buffer for the sliding
> + * window. The window size varies from 1 KB to ZSTD_WINDOWSIZE_MAX
> + * (8 MB), so it is important to use the actual value so as not to
> + * waste memory when it is smaller.
> + */
> + ret = ZSTD_getFrameParams(¶ms, in.src, in.size);
> + err = handle_zstd_error(ret, error);
> + if (err)
> + goto out;
> + if (ret != 0) {
> + error("ZSTD-compressed data has an incomplete frame header");
> + err = -1;
> + goto out;
> + }
> + if (params.windowSize > ZSTD_WINDOWSIZE_MAX) {
> + error("ZSTD-compressed data has too large a window size");
> + err = -1;
> + goto out;
> + }
> +
> + /*
> + * Allocate the ZSTD_DStream now that we know how much memory is
> + * required.
> + */
> + wksp_size = ZSTD_DStreamWorkspaceBound(params.windowSize);
> + wksp = large_malloc(wksp_size);
> + dstream = ZSTD_initDStream(params.windowSize, wksp, wksp_size);
> + if (dstream == NULL) {
> + error("Out of memory while allocating ZSTD_DStream");
> + err = -1;
> + goto out;
> + }
> +
> + /*
> + * Decompression loop:
> + * Read more data if necessary (error if no more data can be read).
> + * Call the decompression function, which returns 0 when finished.
> + * Flush any data produced if using flush().
> + */
> + if (in_pos != NULL)
> + *in_pos = 0;
> + do {
> + /*
> + * If we need to reload data, either we have fill() and can
> + * try to get more data, or we don't and the input is truncated.
> + */
> + if (in.pos == in.size) {
> + if (in_pos != NULL)
> + *in_pos += in.pos;
> + in_len = fill ? fill(in_buf, ZSTD_IOBUF_SIZE) : -1;
> + if (in_len < 0) {
> + error("ZSTD-compressed data is truncated");
> + err = -1;
> + goto out;
> + }
> + in.pos = 0;
> + in.size = in_len;
> + }
> + /* Returns zero when the frame is complete. */
> + ret = ZSTD_decompressStream(dstream, &out, &in);
> + err = handle_zstd_error(ret, error);
> + if (err)
> + goto out;
> + /* Flush all of the data produced if using flush(). */
> + if (flush != NULL && out.pos > 0) {
> + if (out.pos != flush(out.dst, out.pos)) {
> + error("Failed to flush()");
> + err = -1;
> + goto out;
> + }
> + out.pos = 0;
> + }
> + } while (ret != 0);
> +
> + if (in_pos != NULL)
> + *in_pos += in.pos;
> +
> + err = 0;
> +out:
> + if (in_allocated != NULL)
> + free(in_allocated);
> + if (out_allocated != NULL)
> + free(out_allocated);
> + if (wksp != NULL)
> + large_free(wksp);
> + return err;
> +}
> +
> +#ifndef PREBOOT
> +STATIC int INIT unzstd(unsigned char *buf, long len,
> + long (*fill)(void*, unsigned long),
> + long (*flush)(void*, unsigned long),
> + unsigned char *out_buf,
> + long *pos,
> + void (*error)(char *x))
> +{
> + return __unzstd(buf, len, fill, flush, out_buf, 0, pos, error);
> +}
> +#else
> +STATIC int INIT __decompress(unsigned char *buf, long len,
> + long (*fill)(void*, unsigned long),
> + long (*flush)(void*, unsigned long),
> + unsigned char *out_buf, long out_len,
> + long *pos,
> + void (*error)(char *x))
> +{
> + return __unzstd(buf, len, fill, flush, out_buf, out_len, pos, error);
> +}
> +#endif
> --
> 2.25.1
>
--
Kees Cook
