Re: 4.4-rc5: ugly warn on: 5 W+X pages found

Pavel Machek
2015-12-15T20:58:41Z

Hi!

> > 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);
> +}
...
> + if (protval & _PAGE_PRESENT) {
> protval &= __supported_pte_mask;
> + WARN_ON_ONCE(kernel_write_execute_prot(protval));
> + }
>
> return protval;
> }
>
> or similar?
>
> The above is entirely untested. Maybe it doesn't compile. Or
> boot. Or work.

Well, with two extra spaces at each line, it does not apply :-).

I applied it by hand, and the output is:

[ 0.000000] MTRR variable ranges enabled:
[ 0.000000] 0 base 000000000 mask F80000000 write-back
[ 0.000000] 1 base 080000000 mask FC0000000 write-back
[ 0.000000] 2 base 0BF700000 mask FFFF00000 uncachable
[ 0.000000] 3 base 0BF800000 mask FFF800000 uncachable
[ 0.000000] 4 disabled
[ 0.000000] 5 disabled
[ 0.000000] 6 disabled
[ 0.000000] 7 disabled
[ 0.000000] x86/PAT: PAT not supported by CPU.
[ 0.000000] initial memory mapped: [mem 0x00000000-0x05bfffff]
[ 0.000000] Base memory trampoline at [c009b000] 9b000 size 16384
[ 0.000000] ------------[ cut here ]------------
[ 0.000000] WARNING: CPU: 0 PID: 0 at
./arch/x86/include/asm/pgtable.h:357 kernel_physical_mapping_init+0x
256/0x395()
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc5+ #137
[ 0.000000] Hardware name: LENOVO 17097HU/17097HU, BIOS 7BETD8WW
(2.19 ) 03/31/2011
[ 0.000000] 00000000 00000000 c4e63e90 c42baaf8 00000000 c4e63eac
c404066b 00000165
[ 0.000000] c4f134da 00000000 00000000 00000000 c4e63ebc c404070f
00000009 00000000
[ 0.000000] c4e63f18 c4f134da c4e63f00 00000000 00000000 00000000
00000000 00000000
[ 0.000000] Call Trace:
[ 0.000000] [<c42baaf8>] dump_stack+0x41/0x59
[ 0.000000] [<c404066b>] warn_slowpath_common+0x6b/0xa0
[ 0.000000] [<c4f134da>] ?
kernel_physical_mapping_init+0x256/0x395
[ 0.000000] [<c404070f>] warn_slowpath_null+0xf/0x20
[ 0.000000] [<c4f134da>] kernel_physical_mapping_init+0x256/0x395
[ 0.000000] [<c4a4de21>] init_memory_mapping+0x191/0x300
[ 0.000000] [<c4f12d96>] init_mem_mapping+0xe7/0x1f3
[ 0.000000] [<c4f12d96>] ? init_mem_mapping+0xe7/0x1f3
[ 0.000000] [<c4f065ef>] setup_arch+0x659/0x8ca
[ 0.000000] [<c4f0480e>] start_kernel+0xbb/0x360
[ 0.000000] [<c4f042d4>] i386_start_kernel+0x82/0x86
[ 0.000000] ---[ end trace e117245cd61feaf1 ]---
[ 0.000000] BRK [0x0566a000, 0x0566afff] PGTABLE
[ 0.000000] BRK [0x0566b000, 0x0566bfff] PGTABLE
[ 0.000000] BRK [0x0566c000, 0x0566cfff] PGTABLE

I'll take a look if I can figure out what it means...
Pavel

--
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