Messages in this thread Patch in this message | | | Date | Tue, 10 Nov 2009 14:15:37 -0800 | From | Kees Cook <> | Subject | Re: [PATCH v4] [x86] detect and report lack of NX protections |
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On Tue, Nov 10, 2009 at 01:22:18PM -0800, H. Peter Anvin wrote: > Yes, it should be. set_nx() and check_efer() are doing the same thing, > except in different ways, and they are - IMO - *both* doing something > dumb -- although check_efer() is saner.
BTW, it seems like set_nx() should move from init_memory_mapping to setup_arch, since init_memory_mapping can be called twice, but I don't think set_nx needs to be.
Also, disable_nx is only defined in setup_nx.c when "defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)", so I re-arranged the logic to match that.
How about the following clean-up and merge...
--- 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.
Signed-off-by: Kees Cook <kees.cook@canonical.com> --- arch/x86/kernel/setup.c | 2 ++ arch/x86/mm/init.c | 4 ---- arch/x86/mm/setup_nx.c | 31 ++++++++++++++++++++----------- 3 files changed, 22 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c index e09f0e2..72181c1 100644 --- a/arch/x86/kernel/setup.c +++ b/arch/x86/kernel/setup.c @@ -895,6 +895,8 @@ void __init setup_arch(char **cmdline_p) init_gbpages(); + set_nx(); + /* max_pfn_mapped is updated here */ max_low_pfn_mapped = init_memory_mapping(0, max_low_pfn<<PAGE_SHIFT); max_pfn_mapped = max_low_pfn_mapped; diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index 73ffd55..d406c52 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -146,10 +146,6 @@ unsigned long __init_refok init_memory_mapping(unsigned long start, use_gbpages = direct_gbpages; #endif - set_nx(); - if (nx_enabled) - printk(KERN_INFO "NX (Execute Disable) protection: active\n"); - /* Enable PSE if available */ if (cpu_has_pse) set_in_cr4(X86_CR4_PSE); diff --git a/arch/x86/mm/setup_nx.c b/arch/x86/mm/setup_nx.c index 513d8ed..269b668 100644 --- a/arch/x86/mm/setup_nx.c +++ b/arch/x86/mm/setup_nx.c @@ -33,28 +33,37 @@ static int __init noexec_setup(char *str) early_param("noexec", noexec_setup); #endif -#ifdef CONFIG_X86_PAE void __init set_nx(void) { - unsigned int v[4], l, h; - - if (cpu_has_pae && (cpuid_eax(0x80000000) > 0x80000001)) { - cpuid(0x80000001, &v[0], &v[1], &v[2], &v[3]); + if (!cpu_has_nx) { + printk(KERN_NOTICE "Notice: NX (Execute Disable) protection " + "missing in CPU or disabled in BIOS!\n"); + } else { +#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE) + if (disable_nx) + printk(KERN_INFO "NX (Execute Disable) protection: " + "disabled by kernel command line option\n"); + else { +# ifdef CONFIG_X86_PAE + /* 32-bit PAE */ + unsigned int l, h; - if ((v[3] & (1 << 20)) && !disable_nx) { rdmsr(MSR_EFER, l, h); l |= EFER_NX; wrmsr(MSR_EFER, l, h); nx_enabled = 1; __supported_pte_mask |= _PAGE_NX; +# endif + printk(KERN_INFO "NX (Execute Disable) protection: " + "active\n"); } - } -} #else -void set_nx(void) -{ -} + /* 32bit non-PAE kernel, NX cannot be used */ + printk(KERN_NOTICE "Notice: NX (Execute Disable) protection " + "cannot be enabled: non-PAE kernel!\n"); #endif + } +} #ifdef CONFIG_X86_64 void __cpuinit check_efer(void) -- 1.6.5
-- Kees Cook Ubuntu Security Team
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