linux-kernel - Re: [patch 0/5] Support for sanitization flag in low-level page allocator

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Message-Id: <1243539894.6645.85.camel@laptop>
Date:	Thu, 28 May 2009 21:44:54 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Ingo Molnar <mingo@...e.hu>, Rik van Riel <riel@...hat.com>,
	"Larry H." <research@...reption.com>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>, pageexec@...email.hu,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 0/5] Support for sanitization flag in low-level page
 allocator

On Thu, 2009-05-28 at 12:50 +0100, Alan Cox wrote:
> The performance cost of such a security action are NIL when the feature
> is disabled. So the performance cost in the general case is irrelevant.

Not really, much of the code posted in this thread has the form:

int sanitize_all_mem; /* note the lack of __read_mostly */

void some_existing_function()
{
	if (sanitize_all_mem) { /* extra branch */
		/* do stuff */
	}
}

void sanitize_obj(void *obj)
{
	if (!sanitize_all_mem) /* extra branch */
		return;

	/* do stuff */
}


void another_existing_function()
{
	sanitize_obj(obj); /* extra call */
}

That doesn't equal NIL, that equals extra function calls and branches.

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