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Message-ID: <20091109221015.GB5129@outflux.net>
Date: Mon, 9 Nov 2009 14:10:15 -0800
From: Kees Cook <kees.cook@...onical.com>
To: Arjan van de Ven <arjan@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
Pekka Enberg <penberg@...helsinki.fi>,
Jan Beulich <jbeulich@...ell.com>,
Vegard Nossum <vegardno@....uio.no>,
Yinghai Lu <yinghai@...nel.org>,
Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH v4] [x86] detect and report lack of NX protections
It is possible for x86_64 systems to lack the NX bit (see check_efer())
either due to the hardware lacking support or the BIOS having turned
off the CPU capability, so NX status should be reported. Additionally,
anyone booting NX-capable CPUs in 32bit mode without PAE will lack NX
functionality, so this change provides feedback for that case as well.
v2: use "Alert:" instead of "Warning:" to avoid confusion with WARN_ON()
v3: use "Notice:" instead of "Alert:" to avoid confusion with KERN_ALERT,
and switch to KERN_NOTICE, in keeping with its use for "normal but
significant condition" messages.
v4: check that _NX_PAGE is non-zero to avoid setting nx_enabled accidentally.
Signed-off-by: Kees Cook <kees.cook@...onical.com>
---
arch/x86/mm/init.c | 10 ++++++++++
arch/x86/mm/setup_nx.c | 3 +++
2 files changed, 13 insertions(+), 0 deletions(-)
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 73ffd55..d98b43a 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -149,6 +149,16 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
set_nx();
if (nx_enabled)
printk(KERN_INFO "NX (Execute Disable) protection: active\n");
+ else if (cpu_has_pae)
+#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
+ /* PAE kernel, PAE CPU, without NX */
+ printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
+ "missing in CPU or disabled in BIOS!\n");
+#else
+ /* 32bit non-PAE kernel, PAE CPU */
+ printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
+ "cannot be enabled: non-PAE kernel!\n");
+#endif
/* Enable PSE if available */
if (cpu_has_pse)
diff --git a/arch/x86/mm/setup_nx.c b/arch/x86/mm/setup_nx.c
index 513d8ed..1b93231 100644
--- a/arch/x86/mm/setup_nx.c
+++ b/arch/x86/mm/setup_nx.c
@@ -53,6 +53,9 @@ void __init set_nx(void)
#else
void set_nx(void)
{
+ /* notice if _PAGE_NX exists and was removed during check_efer() */
+ if (_PAGE_NX && ((__supported_pte_mask & _PAGE_NX) == _PAGE_NX))
+ nx_enabled = 1;
}
#endif
--
1.6.5
--
Kees Cook
Ubuntu Security Team
--
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