Messages in this thread Patch in this message | | | Date | Wed, 21 Sep 2022 07:41:25 -0000 | From | "tip-bot2 for Dave Hansen" <> | Subject | [tip: x86/mm] x86/mm/32: Fix W^X detection when page tables do not support NX |
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The following commit has been merged into the x86/mm branch of tip:
Commit-ID: 9377ad7b61bff3abfb375d307770d6aa454bc516 Gitweb: https://git.kernel.org/tip/9377ad7b61bff3abfb375d307770d6aa454bc516 Author: Dave Hansen <dave.hansen@intel.com> AuthorDate: Tue, 20 Sep 2022 11:54:54 -07:00 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Wed, 21 Sep 2022 09:32:55 +02:00
x86/mm/32: Fix W^X detection when page tables do not support NX
The x86 MM code now actively refuses to create writable+executable mappings, and warns when there is an attempt to create one.
The 0day test robot ran across a warning triggered by module unloading on 32-bit kernels. This was only seen on CPUs with NX support, but where a 32-bit kernel was built without PAE support.
On those systems, there is no room for the NX bit in the page tables and _PAGE_NX is #defined to 0, breaking some of the W^X detection logic in verify_rwx(). The X86_FEATURE_NX check in there does not do any good here because the CPU itself supports NX.
Fix it by checking for _PAGE_NX support directly instead of checking CPU support for NX.
Note that since _PAGE_NX is actually defined to be 0 at compile-time this fix should also end up letting the compiler optimize away most of verify_rwx() on non-PAE kernels.
Fixes: 652c5bf380ad ("x86/mm: Refuse W^X violations") Reported-by: kernel test robot <yujie.liu@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/all/fcf89147-440b-e478-40c9-228c9fe56691@intel.com/ --- arch/x86/mm/pat/set_memory.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 1a2d637..20b1e24 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -587,7 +587,8 @@ 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)) + /* Only enforce when NX is supported: */ + if (!(__supported_pte_mask & _PAGE_NX)) return new; if (!((pgprot_val(old) ^ pgprot_val(new)) & (_PAGE_RW | _PAGE_NX)))
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