linux-kernel - Re: [PATCH v2 2/3] acpi: allow building without CONFIG_HAS

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZwkrAhBIu4SV6B-O@smile.fi.intel.com>
Date: Fri, 11 Oct 2024 16:41:22 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Arnd Bergmann <arnd@...nel.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Mario Limonciello <mario.limonciello@....com>,
	Jarred White <jarredwhite@...ux.microsoft.com>,
	Perry Yuan <perry.yuan@....com>,
	Easwar Hariharan <eahariha@...ux.microsoft.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] acpi: allow building without CONFIG_HAS_IOPORT

On Fri, Oct 11, 2024 at 11:40:05AM +0000, Arnd Bergmann wrote:
> On Fri, Oct 11, 2024, at 11:12, Andy Shevchenko wrote:
> > On Fri, Oct 11, 2024 at 09:59:46AM +0000, Arnd Bergmann wrote:
> >> On Fri, Oct 11, 2024, at 09:53, Andy Shevchenko wrote:
> >> > On Fri, Oct 11, 2024 at 06:18:18AM +0000, Arnd Bergmann wrote:
> >> >> +	if (!IS_ENABLED(CONFIG_HAS_IOPORT)) {
> >> >> +		*value = BIT_MASK(width);
> >> >> +		return AE_NOT_IMPLEMENTED;
> >> >
> >> > Perhaps it has already been discussed, but why do we need to file value with
> >> > semi-garbage when we know it's invalid anyway?
> >> 
> >> It's not strictly necessary, just precaution for possible callers
> >> that use the resulting data without checking the error code.
> >
> > Do you have any examples of that in the kernel?
> 
> drivers/acpi/processor_throttling.c:            acpi_os_read_port((acpi_io_address) throttling->status_register.
> --
> drivers/cpufreq/acpi-cpufreq.c-
> drivers/cpufreq/acpi-cpufreq.c: acpi_os_read_port(reg->address, &val, reg->bit_width);
> 
> $ git grep ^[^=]*acpi_os_read_port 
> drivers/acpi/processor_throttling.c:            acpi_os_read_port(\ (acpi_io_address) throttling->status_register.
> drivers/cpufreq/acpi-cpufreq.c: acpi_os_read_port(reg->address, &val, reg->bit_width);

May be we can add checks to them, but dunno...

> >> The all-ones data is what an x86 PC would see when an I/O
> >> port is read that is not connected to any device.
> >
> > Yes, but it's not what your code does.
> 
> My bad, I was confused about what BIT_MASK() does.
> I'll change it to "GENMASK(width, 0)", which should
> do what I intended.

Okay. Maybe also adding a comment that it's usual behaviour in response to
the read from non-existing IO port?

(Or for the curios it's all comes from the Data Bus on hardware being Open
 Drain an hence use of pull-up resistors and when there is no response on
 the bus, the default will be "All 1:s").

-- 
With Best Regards,
Andy Shevchenko