linux-kernel - Re: linux-next: build failure after merge of the kspp tree

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Date:   Wed, 9 Mar 2022 08:52:06 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Mark Pearson <markpearson@...ovo.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the kspp tree

On Wed, Mar 09, 2022 at 09:10:29PM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> After merging the kspp tree, today's linux-next build (x86_64
> allmodconfig) failed like this:
> 
> In file included from include/linux/bitops.h:33,
>                  from include/linux/kernel.h:22,
>                  from drivers/platform/x86/thinkpad_acpi.c:37:
> drivers/platform/x86/thinkpad_acpi.c: In function 'tpacpi_dytc_profile_init':
> arch/x86/include/asm/bitops.h:207:22: error: array subscript 'long unsigned int[0]' is partly outside array bounds of 'int[1]' [-Werror=array-bounds]
>   207 |                 (addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
>       |                 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/platform/x86/thinkpad_acpi.c:10385:18: note: while referencing 'output'
> 10385 |         int err, output;
>       |                  ^~~~~~
> 
> Actually the test_bit() in line 10409.
> 
> Caused by commit
> 
>   e1c21608e3cf ("platform/x86: thinkpad_acpi: Add PSC mode support")
> 
> from the drivers-x86 tree interacting with the enablement of
> -Werror=array-bounds.
> 
> I have reverted that commit for today.

Looking at https://lore.kernel.org/all/20220225182505.7234-1-markpearson@lenovo.com/

The problem is with the cast of "int output" to "unsigned long". Past
fixes have either made the variable unsigned long, or adding a new
variable and removal of casts. e.g. this pseudo-patch:

+	unsigned long bits;

	...
+	bits = output;
-	if (test_bit(DYTC_FC_MMC, (void *)&output)) { /* MMC MODE */
+	if (test_bit(DYTC_FC_MMC, &bits)) { /* MMC MODE */

...

-	} else if (test_bit(DYTC_FC_PSC, (void *)&output)) { /*PSC MODE */
+	} else if (test_bit(DYTC_FC_PSC, &bits)) { /*PSC MODE */



-- 
Kees Cook