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authorDave Hansen <dave.hansen@intel.com>2022-09-20 21:54:54 +0300
committerIngo Molnar <mingo@kernel.org>2022-09-21 11:02:55 +0300
commita3d3163fbe690cfec354fc20808adf0629adf8da (patch)
tree5411953f72a9c74f5d3dedd59cb1ac253884330e /arch/x86/mm
parentc0d2e63d4c618185cdd92faae10bdde33a00c25d (diff)
downloadlinux-a3d3163fbe690cfec354fc20808adf0629adf8da.tar.xz
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> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/all/fcf89147-440b-e478-40c9-228c9fe56691@intel.com/
Diffstat (limited to 'arch/x86/mm')
-rw-r--r--arch/x86/mm/pat/set_memory.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 1a2d6376251c..20b1e24baa85 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)))