Message-ID: <ZvVZoOm7R-dZ4N0_@wheatley.k8r.cz>
Date: Thu, 26 Sep 2024 14:54:56 +0200
From: Martin Kletzander <nert.pinx@...il.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] x86/resctrl: Avoid overflow in MB settings in
 bw_validate()

On Tue, Sep 24, 2024 at 10:46:10AM -0700, Reinette Chatre wrote:
>Hi Martin,
>
>On 9/24/24 1:53 AM, Martin Kletzander wrote:
>> The memory bandwidth value was parsed as unsigned long, but later on
>> rounded up and stored in u32.  That could result in an overflow,
>> especially if resctrl is mounted with the "mba_MBps" option.
>>
>> Switch the variable right to u32 and parse it as such.
>>
>> Since the granularity and minimum bandwidth are not used when the
>> software controller is used (resctrl is mounted with the "mba_MBps"),
>> skip the rounding up as well and return early from bw_validate().
>
>Since this patch will flow via the tip tree the changelog needs
>to meet the requirements documented in Documentation/process/maintainer-tip.rst
>Here is an example how the changelog can be when taking into account
>that context, problem, solution needs to be clearly separated with
>everything written in imperative mood:
>
>	The resctrl schemata file supports specifying memory bandwidth
>	associated with the Memory Bandwidth Allocation (MBA) feature
>	via a percentage (this is the default) or bandwidth in MiBps
>	(when resctrl is mounted with the "mba_MBps" option). The allowed
>	range for the bandwidth percentage is from
>	/sys/fs/resctrl/info/MB/min_bandwidth to 100, using a granularity
>	of /sys/fs/resctrl/info/MB/bandwidth_gran. The supported range for
>	the MiBps bandwidth is 0 to U32_MAX.
>
>	There are two issues with parsing of MiBps memory bandwidth:
>	* The user provided MiBps is mistakenly round up to the granularity
>	  that is unique to percentage input.
>	* The user provided MiBps is parsed using unsigned long (thus accepting
>	  values up to ULONG_MAX), and then assigned to u32 that could result in
>	  overflow.
>
>	Do not round up the MiBps value and parse user provided bandwidth as
>	the u32 it is intended to be. Use the appropriate kstrtou32() that
>	can detect out of range values.
>

Great, can I use your commit message then?  I wouldn't be able to write
it as nicely =)

>
>This needs "Fixes" tags. Looks like the following are appropriate:
>Fixes: 8205a078ba78 ("x86/intel_rdt/mba_sc: Add schemata support")
>Fixes: 6ce1560d35f6 ("x86/resctrl: Switch over to the resctrl mbps_val list")
>

It seems to me like this should've been handled in commit 8205a078ba78
("x86/intel_rdt/mba_sc: Add schemata support") which added support for
mba_sc and kept the rounding up of the value while skipping the range
validation.

>> Signed-off-by: Martin Kletzander <nert.pinx@...il.com>
>> Co-developed-by: Reinette Chatre <reinette.chatre@...el.com>
>> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
>
>Please place your SoB at the end. For details about tag ordering
>you can refer to section "Ordering of commit tags" in
>Documentation/process/maintainer-tip.rst
>

I'll go through that docs too, thanks.

>
>>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 19 ++++++++++++-------
>>  1 file changed, 12 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
>> index 50fa1fe9a073..53defc5a6784 100644
>> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
>> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
>> @@ -29,10 +29,10 @@
>>   * hardware. The allocated bandwidth percentage is rounded to the next
>>   * control step available on the hardware.
>>   */
>> -static bool bw_validate(char *buf, unsigned long *data, struct rdt_resource *r)
>> +static bool bw_validate(char *buf, u32 *data, struct rdt_resource *r)
>>  {
>> -	unsigned long bw;
>>  	int ret;
>> +	u32 bw;
>>
>>  	/*
>>  	 * Only linear delay values is supported for current Intel SKUs.
>> @@ -42,14 +42,19 @@ static bool bw_validate(char *buf, unsigned long *data, struct rdt_resource *r)
>>  		return false;
>>  	}
>>
>> -	ret = kstrtoul(buf, 10, &bw);
>> +	ret = kstrtou32(buf, 10, &bw);
>>  	if (ret) {
>> -		rdt_last_cmd_printf("Non-decimal digit in MB value %s\n", buf);
>> +		rdt_last_cmd_printf("Invalid MB value %s\n", buf);
>>  		return false;
>>  	}
>>
>> -	if ((bw < r->membw.min_bw || bw > r->default_ctrl) &&
>> -	    !is_mba_sc(r)) {
>> +	/* Nothing else to do if software controller is enabled. */
>> +	if (is_mba_sc(r)) {
>> +		*data = bw;
>> +		return true;
>> +	}
>> +
>> +	if (bw < r->membw.min_bw || bw > r->default_ctrl) {
>>  		rdt_last_cmd_printf("MB value %ld out of range [%d,%d]\n", bw,
>>  				    r->membw.min_bw, r->default_ctrl);
>
>By now you may have noticed the lkp report [1] catching an issue with my
>code snippet. Could you please take a look? Seems that %u would be appropriate.
>

Yes, I finally got to it and %u should definitely work.  I wanted to go
with what seems more appropriate, PRIu32, but this file does not have
access to it and in order to include inttypes I would have to change the
Makefile too, which seems too much of a change given it takes me this
many tries already :)

However if PRIu32 is preferred I have no problem adjusting the build
process as well.

>>  		return false;
>> @@ -65,7 +70,7 @@ int parse_bw(struct rdt_parse_data *data, struct resctrl_schema *s,
>>  	struct resctrl_staged_config *cfg;
>>  	u32 closid = data->rdtgrp->closid;
>>  	struct rdt_resource *r = s->res;
>> -	unsigned long bw_val;
>> +	u32 bw_val;
>>
>>  	cfg = &d->staged_config[s->conf_type];
>>  	if (cfg->have_new_ctrl) {
>
>Reinette
>
>[1] https://lore.kernel.org/all/202409250046.1Kk0NXVZ-lkp@intel.com/
>
>

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