linux-kernel - [PATCH] module/decompress: use vmalloc() for gzip decompression workspace

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Date:   Wed, 30 Aug 2023 17:58:20 +0200
From:   Andrea Righi <andrea.righi@...onical.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Lucas De Marchi <lucas.demarchi@...el.com>,
        Nick Terrell <terrelln@...com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] module/decompress: use vmalloc() for gzip decompression workspace

Use a similar approach as commit a419beac4a07 ("module/decompress: use
vmalloc() for zstd decompression workspace") and replace kmalloc() with
vmalloc() also for the gzip module decompression workspace.

In this case the workspace is represented by struct inflate_workspace
that can be fairly large for kmalloc() and it can potentially lead to
allocation errors on certain systems:

$ pahole inflate_workspace
struct inflate_workspace {
	struct inflate_state       inflate_state;        /*     0  9544 */
	/* --- cacheline 149 boundary (9536 bytes) was 8 bytes ago --- */
	unsigned char              working_window[32768]; /*  9544 32768 */

	/* size: 42312, cachelines: 662, members: 2 */
	/* last cacheline: 8 bytes */
};

Considering that there is no need to use continuous physical memory,
simply switch to vmalloc() to provide a more reliable in-kernel module
decompression.

Fixes: b1ae6dc41eaa ("module: add in-kernel support for decompressing")
Signed-off-by: Andrea Righi <andrea.righi@...onical.com>
---
 kernel/module/decompress.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/module/decompress.c b/kernel/module/decompress.c
index 87440f714c0c..4156d59be440 100644
--- a/kernel/module/decompress.c
+++ b/kernel/module/decompress.c
@@ -100,7 +100,7 @@ static ssize_t module_gzip_decompress(struct load_info *info,
 	s.next_in = buf + gzip_hdr_len;
 	s.avail_in = size - gzip_hdr_len;
 
-	s.workspace = kmalloc(zlib_inflate_workspacesize(), GFP_KERNEL);
+	s.workspace = vmalloc(zlib_inflate_workspacesize());
 	if (!s.workspace)
 		return -ENOMEM;
 
@@ -138,7 +138,7 @@ static ssize_t module_gzip_decompress(struct load_info *info,
 out_inflate_end:
 	zlib_inflateEnd(&s);
 out:
-	kfree(s.workspace);
+	vfree(s.workspace);
 	return retval;
 }
 #elif defined(CONFIG_MODULE_COMPRESS_XZ)
-- 
2.40.1