Messages in this thread | | | Date | Mon, 09 Nov 2009 15:16:16 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH v4] [x86] detect and report lack of NX protections |
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On 11/09/2009 02:10 PM, Kees Cook wrote: > 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@canonical.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 >
The second clause can only get executed if CONFIG_X86_PAE is unset, which in turn means _PAGE_NX == 0... so that piece of code is meaningless.
It also looks to me that there is no message distinguishing the case when nx_enabled == 1 but disable_nx == 1, and instead we say NX is "active" when in fact it is disabled in the kernel.
-hpa
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