Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 15 Dec 2015 10:40:53 -0800 | Subject | Re: 4.4-rc5: ugly warn on: 5 W+X pages found |
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On Tue, Dec 15, 2015 at 9:45 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Tue, Dec 15, 2015 at 1:40 AM, Pavel Machek <pavel@ucw.cz> wrote: >> >> I tried applying: >> >> [PATCH 1/2] x86_32/mm: Set NX in __supported_pte_mask before enabling >> paging >> >> but I still get >> >> [ 2.691897] x86/mm: Found insecure W+X mapping at address ffe69000/0xffe69000 > > This may be an insane suggestion, but how about we try to detect when > that entry gets set, rather than after the fact. > > Something really brute-force like > > diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h > index 6ec0c8b2e9df..538c9bb239b9 100644 > --- a/arch/x86/include/asm/pgtable.h > +++ b/arch/x86/include/asm/pgtable.h > @@ -337,6 +337,13 @@ static inline pmd_t pmd_clear_soft_dirty(pmd_t pmd) > > #endif /* CONFIG_HAVE_ARCH_SOFT_DIRTY */ > > +static inline int kernel_write_execute_prot(pgprotval_t protval) > +{ > + return !(protval & _PAGE_USER) && > + !(protval & _PAGE_NX) && > + (protval & _PAGE_RW); > +} > + > /* > * Mask out unsupported bits in a present pgprot. Non-present pgprots > * can use those bits for other purposes, so leave them be. > @@ -345,8 +352,10 @@ static inline pgprotval_t massage_pgprot(pgprot_t pgprot) > { > pgprotval_t protval = pgprot_val(pgprot); > > - if (protval & _PAGE_PRESENT) > + if (protval & _PAGE_PRESENT) { > protval &= __supported_pte_mask; > + WARN_ON_ONCE(kernel_write_execute_prot(protval));
Shouldn't we switch those two lines? Arguably trying to set rwx permissions on !PAE is a bug even if it makes no difference, whereas setting rw- and getting rwx because we don't have NX support on the platform or kernel build doesn't indicate a bug.
Anyway, I still think that we should apply my patches for 4.5 because I think they're cleanups, but apparently I guessed wrong as to what was causing Pavel's issue. But your patch would help diagnose it.
--Andy
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