[LTP] [PATCH] cve: Fix kernel symbol finding for meltdown case

[He Zhe]

On 8/20/19 11:17 PM, Jan Stancek wrote:
> ----- Original Message -----
>> From: He Zhe <zhe.he@windriver.com>
>>
>> meltdown case failed as below.
>> safe_file_ops.c:219: BROK: Expected 3 conversions got 2 at meltdown.c:272
> What line doesn't match current pattern?
> I'm not seeing any changes in kallsyms output:
>
> kernel: "%px %c %s\n"
>         "%px %c %s\t[%s]\n"
> LTP:    "%lx %c SYMBOL%c"

Thanks and yes, you're correct.

I just found the root cause and I'll send v2.

find_kernel_symbol is defined to try twice with each of /proc/kallsyms and
/boot/System.map-%s. Currently if the symbol is not found in /proc/kallsyms,
when kernel option CONFIG_KALLSYMS_ALL is disabled, it would stop the case
immediately due to SAFE_FILE_LINES_SCANF.

Zhe

>
>> The case used SAFE_FILE_LINES_SCANF which is a wrapper of vsscanf which
>> cannot
>> extract the symbol name from the following line pattern of kernel symbol
>> table.
> Did you mean "extract symbol address"?
>
>> 01234567 T SYMBOL_NAME
>>
>> Also the original format pattern is not correct.
>>
>> This patch re-writes the symbol extraction process and adds a NULL pointer
>> check.
>>
>> Signed-off-by: He Zhe <zhe.he@windriver.com>
>> ---
>>  testcases/cve/meltdown.c | 38 +++++++++++++++++++++++++++++++-------
>>  1 file changed, 31 insertions(+), 7 deletions(-)
>>
>> diff --git a/testcases/cve/meltdown.c b/testcases/cve/meltdown.c
>> index f78c38b..4c3f3b2 100644
>> --- a/testcases/cve/meltdown.c
>> +++ b/testcases/cve/meltdown.c
>> @@ -248,15 +248,34 @@ set_cache_hit_threshold(void)
>>  static unsigned long
>>  find_symbol_in_file(const char *filename, const char *symname)
>>  {
>> -	unsigned long addr;
>> -	char type;
>> -	int ret, read;
>> -	char fmt[strlen(symname) + 64];
>> +	unsigned long addr = 0;
>> +	int found = 0;
>> +	char line[BUFSIZ] = {0};
>> +	FILE *fp = NULL;
>> +	char *p = NULL;
>> +
>> +	fp = fopen(filename, "r");
>> +	if (fp == NULL) {
>> +		tst_res(TBROK | TERRNO,
>> +			"Failed to open file:%s for symbol:%s",
>> +			filename, symname);
>> +		return 0;
>> +	}
>>  
>> -	sprintf(fmt, "%%lx %%c %s%%c", symname);
>> +	while (fgets(line, BUFSIZ, fp) != NULL) {
>> +		p = strstr(line, symname);
>> +		/* Make sure this line is exactly for this symbol.
>> +		 * Substract the EOL added by fgets for each line.
>> +		 */
>> +		if (p && ((strlen(p) - 1) == strlen(symname))) {
>> +			found = sscanf(line, "%lx", &addr);
>> +			if (found == 1)
>> +				break;
>> +		}
>> +	}
>> +	fclose(fp);
>>  
>> -	ret = SAFE_FILE_LINES_SCANF(filename, fmt, &addr, &type, &read);
>> -	if (ret)
>> +	if (found != 1)
>>  		return 0;
>>  
>>  	return addr;
>> @@ -322,6 +341,11 @@ static void run(void)
>>  
>>  	/* read address of saved_cmdline_addr */
>>  	addr = saved_cmdline_addr;
>> +	if (!addr) {
>> +		tst_res(TBROK | TERRNO, "saved_cmdline_addr is 0\n");
>> +		return;
>> +	}
>> +
>>  	size = sizeof(addr);
>>  	for (i = 0; i < size; i++) {
>>  		ret = readbyte(spec_fd, addr);
>> --
>> 2.7.4
>>
>>
>> --
>> Mailing list info: https://lists.linux.it/listinfo/ltp
>>