Messages in this thread Patch in this message | | | Date | Mon, 9 Nov 2009 14:10:15 -0800 | From | Kees Cook <> | Subject | [PATCH v4] [x86] detect and report lack of NX protections |
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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 -- 1.6.5
-- Kees Cook Ubuntu Security Team
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