linux-hardening - Re: [PATCH v4 2/8] overflow: Add struct_size_with_data() and struct_data

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Message-ID: <Zd-q20FkC_3DQ14i@smile.fi.intel.com>
Date: Wed, 28 Feb 2024 23:51:23 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Kees Cook <keescook@...omium.org>
Cc: Vinod Koul <vkoul@...nel.org>, Linus Walleij <linus.walleij@...aro.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Mark Brown <broonie@...nel.org>,
	linux-arm-kernel@...ts.infradead.org, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	linux-spi@...r.kernel.org, netdev@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: [PATCH v4 2/8] overflow: Add struct_size_with_data() and
 struct_data_pointer() helpers

On Wed, Feb 28, 2024 at 01:37:36PM -0800, Kees Cook wrote:
> On Wed, Feb 28, 2024 at 10:41:32PM +0200, Andy Shevchenko wrote:

...

> > +#define struct_data_pointer(p, a)	PTR_ALIGN((void *)((p) + 1), (a))
> 
> I'm not super excited about propagating the "p + 1" code pattern to find
> things after an allocation. This leads to the compiler either being
> blind to accesses beyond an allocation, or being too conservative about
> accesses beyond an object. Instead of these helpers I would much prefer
> that data structures that use this code pattern be converted to using
> trailing flexible arrays, at which point the compiler is in a much
> better position to reason about sizes.

There is nothing about flexible arrays in this.
Maybe you have been confused by my choice for name of the macros.
In that case I also can argue that current struct_size() is a good one.
(something like struct_size_with_flex_array() can be more specific)

-- 
With Best Regards,
Andy Shevchenko