Re: [PATCH 5/5] x86, pti: filter at vma->vm_page_prot population

Nadav Amit
2018-04-21T01:21:01Z

Dave Hansen <dave.hansen@linux.intel.com> wrote:

>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> 0day reported warnings at boot on 32-bit systems without NX support:
>
> [ 12.349193] attempted to set unsupported pgprot: 8000000000000025 bits: 8000000000000000 supported: 7fffffffffffffff
> [ 12.350792] WARNING: CPU: 0 PID: 1 at arch/x86/include/asm/pgtable.h:540 handle_mm_fault+0xfc1/0xfe0:
> check_pgprot at arch/x86/include/asm/pgtable.h:535
> (inlined by) pfn_pte at arch/x86/include/asm/pgtable.h:549
> (inlined by) do_anonymous_page at mm/memory.c:3169
> (inlined by) handle_pte_fault at mm/memory.c:3961
> (inlined by) __handle_mm_fault at mm/memory.c:4087
> (inlined by) handle_mm_fault at mm/memory.c:4124
>
> The problem was that we stopped massaging page permissions at PTE creation
> time, so vma->vm_page_prot was passed unfiltered to PTE creation.
>
> To fix it, filter the page protections before they are installed in
> vma->vm_page_prot.
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Reported-by: Fengguang Wu <fengguang.wu@intel.com>
> Fixes: fb43d6cb91 ("x86/mm: Do not auto-massage page protections")
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Kees Cook <keescook@google.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Nadav Amit <namit@vmware.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: linux-mm@kvack.org
> Cc: Ingo Molnar <mingo@kernel.org>
> ---
>
> b/arch/x86/Kconfig | 4 ++++
> b/arch/x86/include/asm/pgtable.h | 5 +++++
> b/mm/mmap.c | 11 ++++++++++-
> 3 files changed, 19 insertions(+), 1 deletion(-)
>
> diff -puN arch/x86/include/asm/pgtable.h~pti-glb-protection_map arch/x86/include/asm/pgtable.h
> --- a/arch/x86/include/asm/pgtable.h~pti-glb-protection_map 2018-04-20 14:10:08.251749151 -0700
> +++ b/arch/x86/include/asm/pgtable.h 2018-04-20 14:10:08.260749151 -0700
> @@ -601,6 +601,11 @@ static inline pgprot_t pgprot_modify(pgp
>
> #define canon_pgprot(p) __pgprot(massage_pgprot(p))
>
> +static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
> +{
> + return canon_pgprot(prot);
> +}
> +
> static inline int is_new_memtype_allowed(u64 paddr, unsigned long size,
> enum page_cache_mode pcm,
> enum page_cache_mode new_pcm)
> diff -puN arch/x86/Kconfig~pti-glb-protection_map arch/x86/Kconfig
> --- a/arch/x86/Kconfig~pti-glb-protection_map 2018-04-20 14:10:08.253749151 -0700
> +++ b/arch/x86/Kconfig 2018-04-20 14:10:08.260749151 -0700
> @@ -52,6 +52,7 @@ config X86
> select ARCH_HAS_DEVMEM_IS_ALLOWED
> select ARCH_HAS_ELF_RANDOMIZE
> select ARCH_HAS_FAST_MULTIPLIER
> + select ARCH_HAS_FILTER_PGPROT
> select ARCH_HAS_FORTIFY_SOURCE
> select ARCH_HAS_GCOV_PROFILE_ALL
> select ARCH_HAS_KCOV if X86_64
> @@ -273,6 +274,9 @@ config ARCH_HAS_CPU_RELAX
> config ARCH_HAS_CACHE_LINE_SIZE
> def_bool y
>
> +config ARCH_HAS_FILTER_PGPROT
> + def_bool y
> +
> config HAVE_SETUP_PER_CPU_AREA
> def_bool y
>
> diff -puN mm/mmap.c~pti-glb-protection_map mm/mmap.c
> --- a/mm/mmap.c~pti-glb-protection_map 2018-04-20 14:10:08.256749151 -0700
> +++ b/mm/mmap.c 2018-04-20 14:10:08.261749151 -0700
> @@ -100,11 +100,20 @@ pgprot_t protection_map[16] __ro_after_i
> __S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
> };
>
> +#ifndef CONFIG_ARCH_HAS_FILTER_PGPROT
> +static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
> +{
> + return prot;
> +}
> +#endif
> +
> pgprot_t vm_get_page_prot(unsigned long vm_flags)
> {
> - return __pgprot(pgprot_val(protection_map[vm_flags &
> + pgprot_t ret = __pgprot(pgprot_val(protection_map[vm_flags &
> (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
> pgprot_val(arch_vm_get_page_prot(vm_flags)));
> +
> + return arch_filter_pgprot(ret);
> }
> EXPORT_SYMBOL(vm_get_page_prot);

Wouldn’t it be simpler or at least cleaner to change the protection map if
NX is not supported? I presume it can be done paging_init() similarly to the
way other archs (e.g., arm, mips) do.