Messages in this thread Patch in this message | | | Date | Tue, 20 Sep 2022 11:12:22 +0800 | From | Yujie Liu <> | Subject | Re: [PATCH] x86/mm: Set NX bit when making pages present |
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On Mon, Sep 19, 2022 at 11:30:09AM -0700, Dave Hansen wrote: > On 9/19/22 11:14, Edgecombe, Rick P wrote: > > Clearly somehow it is though. The original report has this in the log: > > Notice: NX (Execute Disable) protection cannot be enabled: non-PAE > > kernel! > > Ah, crud. Nice catch, btw. > > So, the CPU has NX, making cpu_feature_enabled(X86_FEATURE_NX)==1, but > the page table mode does not have support. > > I guess we can either clear X86_FEATURE_NX around the "protection cannot > be enabled" message, or do something like the attached patch and just do > the check at runtime. > > I'm not sure we want to mess with X86_FEATURE_NX itself. It seems to > get used for a few different things, including on the KVM side. > > 0day folks, can you see if _this_ one (totally untested) helps the > situation? At least this is a real oddball case. It's not something > that folks are very likely to hit at all.
This patch fixes the issues in below two reports. Thanks.
https://lore.kernel.org/all/fcf89147-440b-e478-40c9-228c9fe56691@intel.com/ https://lore.kernel.org/all/202209141701.e293ea84-yujie.liu@intel.com/
Comparison of test results:
========================================================================================= compiler/kconfig/rootfs/runtime/scale_type/tbox_group/testcase: gcc-11/i386-randconfig-a013-20211012/debian-i386-20191205.cgz/300s/srcu/vm-snb/rcuscale
commit: 652c5bf380ad01 ("x86/mm: Refuse W^X violations") 0718e6a68e2a7c ("nx.patch")
652c5bf380ad018e 0718e6a68e2a7cb20800b1b1372 ---------------- --------------------------- fail:runs %reproduction fail:runs | | | 6:6 -100% :6 dmesg.BUG:unable_to_handle_page_fault_for_address 6:6 -100% :6 dmesg.EIP:__change_page_attr 6:6 -100% :6 dmesg.Kernel_panic-not_syncing:Fatal_exception 6:6 -100% :6 dmesg.Oops:#[##] 6:6 -100% :6 dmesg.WARNING:at_arch/x86/mm/pat/set_memory.c:#__change_page_attr
========================================================================================= compiler/kconfig/rootfs/runtime/tbox_group/test/testcase/torture_type: gcc-11/i386-randconfig-a004-20211104/debian-i386-20191205.cgz/300s/vm-snb/cpuhotplug/rcutorture/tasks-tracing
commit: 652c5bf380ad01 ("x86/mm: Refuse W^X violations") 0718e6a68e2a7c ("nx.patch")
652c5bf380ad018e 0718e6a68e2a7cb20800b1b1372 ---------------- --------------------------- fail:runs %reproduction fail:runs | | | 6:6 -100% :6 dmesg.BUG:unable_to_handle_page_fault_for_address 6:6 -100% :6 dmesg.EIP:verify_rwx 6:6 -100% :6 dmesg.Kernel_panic-not_syncing:Fatal_exception 6:6 -100% :6 dmesg.Oops:#[##] 6:6 -100% :6 dmesg.WARNING:at_arch/x86/mm/pat/set_memory.c:#verify_rwx
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index 216fee7144ee..005492257abb 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -844,6 +844,7 @@ static void __init x86_report_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"); > + __supported_pte_mask &= ~_PAGE_NX; > #endif > } > } > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c > index 1a2d6376251c..f8162fe94bd0 100644 > --- a/arch/x86/mm/pat/set_memory.c > +++ b/arch/x86/mm/pat/set_memory.c > @@ -587,7 +587,7 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star > { > unsigned long end; > > - if (!cpu_feature_enabled(X86_FEATURE_NX)) > + if (!(__supported_pte_mask & _PAGE_NX)) > return new; > > if (!((pgprot_val(old) ^ pgprot_val(new)) & (_PAGE_RW | _PAGE_NX)))
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