linux-kernel - Possible bug for ZSTD kernel decompressing

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Date:   Fri, 28 Jan 2022 12:53:30 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Nick Terrell <terrelln@...com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
        kernel test robot <oliver.sang@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Possible bug for ZSTD kernel decompressing

Hi All,

Recently 0Day reported a 32bit i386 kernel decompression failure for my
patch [1], which essentially increase the kernel data section's size
from 19MB to 53MB, with error message:

	early console in setup code
	early console in extract_kernel
	input_data: 0x05077079
	input_len: 0x00f8a633
	output: 0x01000000
	output_len: 0x045c4328
	kernel_total_size: 0x05040000
	needed_size: 0x05040000

	Decompressing Linux... 

	ZSTD-compressed data is corrupt

	 -- System haltedBUG: kernel hang in boot stage

>From debug, it is likely a problem of ZSTD decompression code, as when I
reverted my patch and  hacked to increase the size of kernel data
section by 32MB, the same error will happen.

Some other hints are:
* same i386 config with lz4 and xz algo can boot
* X86_64 + zstd also boots fine

This could be reproduced by qemu cmd:

qemu-system-i386 -machine pc -cpu host -enable-kvm -kernel bzImage -m 2048m -smp 4 -serial stdio  --append "earlyprintk=ttyS0,115200 console=ttyS0,115200"

i386 kernel config is attached, and the debug patch as below:
---
diff --git a/init/main.c b/init/main.c
index 767ee2672176..873f40ddf96e 100644
--- a/init/main.c
+++ b/init/main.c
@@ -162,6 +162,10 @@ static size_t initargs_offs;
 static char *execute_command;
 static char *ramdisk_execute_command = "/init";
 
+#define DT_SIZE		8192000
+static unsigned long tbuf[DT_SIZE] = { 1, 2, 3, 4, };
+
 /*
  * Used to generate warnings if static_key manipulation functions are used
  * before jump_label_init is called.
@@ -690,6 +694,11 @@ noinline void __ref rest_init(void)
 	struct task_struct *tsk;
 	int pid;
 
+	unsigned long i, j;
+	for (i = 0; i < DT_SIZE; i++)
+		j += tbuf[i];
+	printk("j = 0x%x\n", j);
+
 	rcu_scheduler_starting();
 	/*
 	 * We need to spawn init first so that it obtains pid 1, however

Please let me know if you need more info.

[1.] https://lore.kernel.org/lkml/1627456900-42743-1-git-send-email-feng.tang@intel.com/ 

Thanks,
Feng

View attachment "i386_decompress_fail.config" of type "text/plain" (146586 bytes)