Commit 438b8050 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Kees Cook
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pstore: Replace crypto API compression with zlib_deflate library calls 



Pstore supports compression using a variety of algorithms exposed by the
crypto API. This uses the deprecated comp (as opposed to scomp/acomp)
API, and so we should stop using that, and either move to the new API,
or switch to a different approach entirely.

Given that we only compress ASCII text in pstore, and considering that
this happens when the system is likely to be in an unstable state, the
flexibility that the complex crypto API provides does not outweigh its
impact on the risk that we might encounter additional problems when
trying to commit the kernel log contents to the pstore backend.

So let's switch [back] to the zlib deflate library API, and remove all
the complexity that really has no place in a low-level diagnostic
facility. Note that, while more modern compression algorithms have been
added to the kernel in recent years, the code size of zlib deflate is
substantially smaller than, e.g., zstd, while its performance in terms
of compression ratio is comparable for ASCII text, and speed is deemed
irrelevant in this context.

Note that this means that compressed pstore records may no longer be
accessible after a kernel upgrade, but this has never been part of the
contract. (The choice of compression algorithm is not stored in the
pstore records either)

Tested-by: "Guilherme G. Piccoli" <gpiccoli@igalia.com> # Steam Deck
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20230712162332.2670437-3-ardb@kernel.org


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 1756ddea

fs/pstore/Kconfig

+9 −91
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0-only

config PSTORE

	tristate "Persistent store support"

	select CRYPTO if PSTORE_COMPRESS

	default n

	help

	   This option enables generic access to platform level
@@ -22,99 +21,18 @@ config PSTORE_DEFAULT_KMSG_BYTES 
	  Defines default size of pstore kernel log storage.

	  Can be enlarged if needed, not recommended to shrink it.



config PSTORE_DEFLATE_COMPRESS

	tristate "DEFLATE (ZLIB) compression"

	default y

	depends on PSTORE

	select CRYPTO_DEFLATE

	help

	  This option enables DEFLATE (also known as ZLIB) compression

	  algorithm support.



config PSTORE_LZO_COMPRESS

	tristate "LZO compression"

	depends on PSTORE

	select CRYPTO_LZO

	help

	  This option enables LZO compression algorithm support.



config PSTORE_LZ4_COMPRESS

	tristate "LZ4 compression"

	depends on PSTORE

	select CRYPTO_LZ4

	help

	  This option enables LZ4 compression algorithm support.



config PSTORE_LZ4HC_COMPRESS

	tristate "LZ4HC compression"

	depends on PSTORE

	select CRYPTO_LZ4HC

	help

	  This option enables LZ4HC (high compression) mode algorithm.



config PSTORE_842_COMPRESS

	bool "842 compression"

	depends on PSTORE

	select CRYPTO_842

	help

	  This option enables 842 compression algorithm support.



config PSTORE_ZSTD_COMPRESS

	bool "zstd compression"

	depends on PSTORE

	select CRYPTO_ZSTD

	help

	  This option enables zstd compression algorithm support.



config PSTORE_COMPRESS

	def_bool y

	bool "Pstore compression (deflate)"

	depends on PSTORE

	depends on PSTORE_DEFLATE_COMPRESS || PSTORE_LZO_COMPRESS ||	\

		   PSTORE_LZ4_COMPRESS || PSTORE_LZ4HC_COMPRESS ||	\

		   PSTORE_842_COMPRESS || PSTORE_ZSTD_COMPRESS



choice

	prompt "Default pstore compression algorithm"

	depends on PSTORE_COMPRESS

	select ZLIB_INFLATE

	select ZLIB_DEFLATE

	default y

	help

	  This option chooses the default active compression algorithm.

	  This change be changed at boot with "pstore.compress=..." on

	  the kernel command line.



	  Currently, pstore has support for 6 compression algorithms:

	  deflate, lzo, lz4, lz4hc, 842 and zstd.



	  The default compression algorithm is deflate.



	config PSTORE_DEFLATE_COMPRESS_DEFAULT

		bool "deflate" if PSTORE_DEFLATE_COMPRESS



	config PSTORE_LZO_COMPRESS_DEFAULT

		bool "lzo" if PSTORE_LZO_COMPRESS



	config PSTORE_LZ4_COMPRESS_DEFAULT

		bool "lz4" if PSTORE_LZ4_COMPRESS



	config PSTORE_LZ4HC_COMPRESS_DEFAULT

		bool "lz4hc" if PSTORE_LZ4HC_COMPRESS



	config PSTORE_842_COMPRESS_DEFAULT

		bool "842" if PSTORE_842_COMPRESS



	config PSTORE_ZSTD_COMPRESS_DEFAULT

		bool "zstd" if PSTORE_ZSTD_COMPRESS



endchoice



config PSTORE_COMPRESS_DEFAULT

	string

	depends on PSTORE_COMPRESS

	default "deflate" if PSTORE_DEFLATE_COMPRESS_DEFAULT

	default "lzo" if PSTORE_LZO_COMPRESS_DEFAULT

	default "lz4" if PSTORE_LZ4_COMPRESS_DEFAULT

	default "lz4hc" if PSTORE_LZ4HC_COMPRESS_DEFAULT

	default "842" if PSTORE_842_COMPRESS_DEFAULT

	default "zstd" if PSTORE_ZSTD_COMPRESS_DEFAULT

	  Whether pstore records should be compressed before being written to

	  the backing store. This is implemented using the zlib 'deflate'

	  algorithm, using the library implementation instead of using the full

	  blown crypto API. This reduces the risk of secondary oopses or other

	  problems while pstore is recording panic metadata.



config PSTORE_CONSOLE

	bool "Log kernel console messages"

fs/pstore/platform.c

+88 −48
Original line number Diff line number Diff line
@@ -16,13 +16,14 @@ 
#include <linux/console.h>

#include <linux/module.h>

#include <linux/pstore.h>

#include <linux/crypto.h>

#include <linux/string.h>

#include <linux/timer.h>

#include <linux/slab.h>

#include <linux/uaccess.h>

#include <linux/jiffies.h>

#include <linux/vmalloc.h>

#include <linux/workqueue.h>

#include <linux/zlib.h>



#include "internal.h"
@@ -71,12 +72,21 @@ static char *backend; 
module_param(backend, charp, 0444);

MODULE_PARM_DESC(backend, "specific backend to use");



static char *compress =

#ifdef CONFIG_PSTORE_COMPRESS_DEFAULT

		CONFIG_PSTORE_COMPRESS_DEFAULT;

#else

		NULL;

#endif

/*

 * pstore no longer implements compression via the crypto API, and only

 * supports zlib deflate compression implemented using the zlib library

 * interface. This removes additional complexity which is hard to justify for a

 * diagnostic facility that has to operate in conditions where the system may

 * have become unstable. Zlib deflate is comparatively small in terms of code

 * size, and compresses ASCII text comparatively well. In terms of compression

 * speed, deflate is not the best performer but for recording the log output on

 * a kernel panic, this is not considered critical.

 *

 * The only remaining arguments supported by the compress= module parameter are

 * 'deflate' and 'none'. To retain compatibility with existing installations,

 * all other values are logged and replaced with 'deflate'.

 */

static char *compress = "deflate";

module_param(compress, charp, 0444);

MODULE_PARM_DESC(compress, "compression to use");
@@ -85,8 +95,7 @@ unsigned long kmsg_bytes = CONFIG_PSTORE_DEFAULT_KMSG_BYTES; 
module_param(kmsg_bytes, ulong, 0444);

MODULE_PARM_DESC(kmsg_bytes, "amount of kernel log to snapshot (in bytes)");



/* Compression parameters */

static struct crypto_comp *tfm;

static void *compress_workspace;



static char *big_oops_buf;
@@ -156,36 +165,49 @@ static bool pstore_cannot_block_path(enum kmsg_dump_reason reason) 
static int pstore_compress(const void *in, void *out,

			   unsigned int inlen, unsigned int outlen)

{

	struct z_stream_s zstream = {

		.next_in	= in,

		.avail_in	= inlen,

		.next_out	= out,

		.avail_out	= outlen,

		.workspace	= compress_workspace,

	};

	int ret;



	if (!IS_ENABLED(CONFIG_PSTORE_COMPRESS))

		return -EINVAL;



	ret = crypto_comp_compress(tfm, in, inlen, out, &outlen);

	if (ret) {

		pr_err("crypto_comp_compress failed, ret = %d!\n", ret);

		return ret;

	}

	ret = zlib_deflateInit2(&zstream, Z_DEFAULT_COMPRESSION, Z_DEFLATED,

				-MAX_WBITS, DEF_MEM_LEVEL, Z_DEFAULT_STRATEGY);

	if (ret != Z_OK)

		return -EINVAL;



	ret = zlib_deflate(&zstream, Z_FINISH);

	if (ret != Z_STREAM_END)

		return -EINVAL;



	ret = zlib_deflateEnd(&zstream);

	if (ret != Z_OK)

		pr_warn_once("zlib_deflateEnd() failed: %d\n", ret);



	return outlen;

	return zstream.total_out;

}



static void allocate_buf_for_compression(void)

{

	struct crypto_comp *ctx;

	char *buf;



	/* Skip if not built-in or compression backend not selected yet. */

	if (!IS_ENABLED(CONFIG_PSTORE_COMPRESS) || !compress)

		return;



	/* Skip if no pstore backend yet or compression init already done. */

	if (!psinfo || tfm)

	/* Skip if not built-in or compression disabled. */

	if (!IS_ENABLED(CONFIG_PSTORE_COMPRESS) || !compress ||

	    !strcmp(compress, "none")) {

		compress = NULL;

		return;

	}



	if (!crypto_has_comp(compress, 0, 0)) {

		pr_err("Unknown compression: %s\n", compress);

		return;

	if (strcmp(compress, "deflate")) {

		pr_err("Unsupported compression '%s', falling back to deflate\n",

		       compress);

		compress = "deflate";

	}



	/*
@@ -200,16 +222,15 @@ static void allocate_buf_for_compression(void) 
		return;

	}



	ctx = crypto_alloc_comp(compress, 0, 0);

	if (IS_ERR_OR_NULL(ctx)) {

	compress_workspace =

		vmalloc(zlib_deflate_workspacesize(MAX_WBITS, DEF_MEM_LEVEL));

	if (!compress_workspace) {

		pr_err("Failed to allocate zlib deflate workspace\n");

		kfree(buf);

		pr_err("crypto_alloc_comp('%s') failed: %ld\n", compress,

		       PTR_ERR(ctx));

		return;

	}



	/* A non-NULL big_oops_buf indicates compression is available. */

	tfm = ctx;

	big_oops_buf = buf;



	pr_info("Using crash dump compression: %s\n", compress);
@@ -217,10 +238,11 @@ static void allocate_buf_for_compression(void) 


static void free_buf_for_compression(void)

{

	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && tfm) {

		crypto_free_comp(tfm);

		tfm = NULL;

	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && compress_workspace) {

		vfree(compress_workspace);

		compress_workspace = NULL;

	}



	kfree(big_oops_buf);

	big_oops_buf = NULL;

}
@@ -531,7 +553,8 @@ void pstore_unregister(struct pstore_info *psi) 
}

EXPORT_SYMBOL_GPL(pstore_unregister);



static void decompress_record(struct pstore_record *record)

static void decompress_record(struct pstore_record *record,

			      struct z_stream_s *zstream)

{

	int ret;

	int unzipped_len;
@@ -547,26 +570,37 @@ static void decompress_record(struct pstore_record *record) 
	}



	/* Missing compression buffer means compression was not initialized. */

	if (!big_oops_buf) {

	if (!zstream->workspace) {

		pr_warn("no decompression method initialized!\n");

		return;

	}



	ret = zlib_inflateReset(zstream);

	if (ret != Z_OK) {

		pr_err("zlib_inflateReset() failed, ret = %d!\n", ret);

		return;

	}



	/* Allocate enough space to hold max decompression and ECC. */

	workspace = kmalloc(psinfo->bufsize + record->ecc_notice_size,

			    GFP_KERNEL);

	if (!workspace)

		return;



	/* After decompression "unzipped_len" is almost certainly smaller. */

	ret = crypto_comp_decompress(tfm, record->buf, record->size,

					  workspace, &unzipped_len);

	if (ret) {

		pr_err("crypto_comp_decompress failed, ret = %d!\n", ret);

	zstream->next_in	= record->buf;

	zstream->avail_in	= record->size;

	zstream->next_out	= workspace;

	zstream->avail_out	= psinfo->bufsize;



	ret = zlib_inflate(zstream, Z_FINISH);

	if (ret != Z_STREAM_END) {

		pr_err("zlib_inflate() failed, ret = %d!\n", ret);

		kfree(workspace);

		return;

	}



	unzipped_len = zstream->total_out;



	/* Append ECC notice to decompressed buffer. */

	memcpy(workspace + unzipped_len, record->buf + record->size,

	       record->ecc_notice_size);
@@ -596,10 +630,17 @@ void pstore_get_backend_records(struct pstore_info *psi, 
{

	int failed = 0;

	unsigned int stop_loop = 65536;

	struct z_stream_s zstream = {};



	if (!psi || !root)

		return;



	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && compress) {

		zstream.workspace = kvmalloc(zlib_inflate_workspacesize(),

					     GFP_KERNEL);

		zlib_inflateInit2(&zstream, -DEF_WBITS);

	}



	mutex_lock(&psi->read_mutex);

	if (psi->open && psi->open(psi))

		goto out;
@@ -628,7 +669,7 @@ void pstore_get_backend_records(struct pstore_info *psi, 
			break;

		}



		decompress_record(record);

		decompress_record(record, &zstream);

		rc = pstore_mkfile(root, record);

		if (rc) {

			/* pstore_mkfile() did not take record, so free it. */
@@ -644,6 +685,12 @@ void pstore_get_backend_records(struct pstore_info *psi, 
out:

	mutex_unlock(&psi->read_mutex);



	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && compress) {

		if (zlib_inflateEnd(&zstream) != Z_OK)

			pr_warn("zlib_inflateEnd() failed\n");

		kvfree(zstream.workspace);

	}



	if (failed)

		pr_warn("failed to create %d record(s) from '%s'\n",

			failed, psi->name);
@@ -671,13 +718,6 @@ static int __init pstore_init(void) 
{

	int ret;



	/*

	 * Check if any pstore backends registered earlier but did not

	 * initialize compression because crypto was not ready. If so,

	 * initialize compression now.

	 */

	allocate_buf_for_compression();



	ret = pstore_init_fs();

	if (ret)

		free_buf_for_compression();