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SubjectRe: [PATCH v2] x86: consider effective protection attributes in W+X check
>>> On 23.02.18 at 08:49, <mingo@kernel.org> wrote:

> * Jan Beulich <JBeulich@suse.com> wrote:
>
>> >>> On 21.02.18 at 17:53, <mingo@kernel.org> wrote:
>>
>> > * Jan Beulich <JBeulich@suse.com> wrote:
>> >
>> >> Using just the leaf page table entry flags would cause a false warning
>> >> in case _PAGE_RW is clear or _PAGE_NX is set in a higher level entry.
>> >> Hand through both the current entry's flags as well as the accumulated
>> >> effective value (the latter as pgprotval_t instead of pgprot_t, as it's
>> >> not an actual entry's value).
>> >>
>> >> This in particular eliminates the false W+X warning when running under
>> >> Xen, as commit 2cc42bac1c ("x86-64/Xen: eliminate W+X mappings") has to
>> >> make the necessary adjustment in L2 rather than L1 (the reason is
>> >> explained there). I.e. _PAGE_RW is clear there in L1, but _PAGE_NX is
>> >> set in L2.
>> >>
>> >> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> >> Reviewed-by: Juergen Gross <jgross@suse.com>
>> >> ---
>> >> v2: Re-base onto tip tree. Add Xen related paragraph to description.
>> >> ---
>> >> arch/x86/mm/dump_pagetables.c | 92
>> > ++++++++++++++++++++++++++----------------
>> >> 1 file changed, 57 insertions(+), 35 deletions(-)
>> >
>> > There's a build failure with CONFIG_KASAN=y enabled:
>> >
>> > arch/x86/mm/dump_pagetables.c: In function ‘kasan_page_table’:
>> > arch/x86/mm/dump_pagetables.c:365:3: error: too few arguments to function ‘note_page’
>> > arch/x86/mm/dump_pagetables.c:238:13: note: declared here
>>
>> Oh, I see. Question though is what to pass as the extra argument:
>> Do I need to pass in the caller's effective rights, or should I take
>> kasan_page_table()'s checking against kasan_zero_p?d as an
>> indication that the effective permission is zero here? I'm sorry for
>> this probably trivial question, but I know nothing about how KASAN
>> works.
>
> I'm not sure either - but I've Cc:-ed the KASAN gents who might be able to
> help us out here?

Actually, the "zero" in the names of the symbols meanwhile makes
me be pretty sure passing 0 for the effective permissions here is
exactly what is wanted. I'm about to produce v3.

Jan

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