linux-kernel - [PATCH] [29/31] CPA: Add a BUG_ON checking for someone setting the kernel text NX

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Date:	Mon, 14 Jan 2008 23:17:02 +0100 (CET)
From:	Andi Kleen <ak@...e.de>
To:	linux-kernel@...r.kernel.org, jbeulich@...ell.com, mingo@...e.hu,
	tglx@...utronix.de
Subject: [PATCH] [29/31] CPA: Add a BUG_ON checking for someone setting the kernel text NX


Someone setting NX on the kernel text tends to result in nasty failures
and triple faults, so BUG_ON early for that.

Does not cover __inittext.

Signed-off-by: Andi Kleen <ak@...e.de>

---
 arch/x86/mm/pageattr_32.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linux/arch/x86/mm/pageattr_32.c
===================================================================
--- linux.orig/arch/x86/mm/pageattr_32.c
+++ linux/arch/x86/mm/pageattr_32.c
@@ -242,6 +242,14 @@ __change_page_attr(struct page *page, pg
 	BUG_ON(PageLRU(kpte_page));
 	BUG_ON(PageCompound(kpte_page));
 
+	/*
+	 * Better fail early if someone sets the kernel text to NX.
+	 * Does not cover __inittext
+	 */
+	BUG_ON(address >= (unsigned long)&_text &&
+		address < (unsigned long)&_etext &&
+	       (pgprot_val(prot) & _PAGE_NX));
+
 	set_tlb_flush(address, cache_attr_changed(*kpte, prot, level),
 			level < 3);
 
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