| Message ID | 20220911095923.3614387-2-pasha.tatashin@soleen.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | page table check default to warn instead of panic | expand |
On Sun, 2022-09-11 at 09:59 +0000, Pasha Tatashin wrote: > From: Rick Edgecombe <rick.p.edgecombe@intel.com> > > The zero page should remain all zero, so that it can be mapped as > read-only for read faults of memory that should be zeroed. If it is > ever > mapped writable to userspace, it could become non-zero and so other > apps > would unexpectedly get non-zero data. So the zero page should never > be > mapped writable to userspace. Check for this condition in > page_table_check_set(). > > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com> > --- > mm/page_table_check.c | 2 ++ > 1 file changed, 2 insertions(+) > Thanks. Should we put this at the end, in order to not add any more BUG_ON()'s to the kernel? Or I can just send a follow up and add the docs you asked for.
On 11.09.22 11:59, Pasha Tatashin wrote: > From: Rick Edgecombe <rick.p.edgecombe@intel.com> > > The zero page should remain all zero, so that it can be mapped as > read-only for read faults of memory that should be zeroed. If it is ever > mapped writable to userspace, it could become non-zero and so other apps > would unexpectedly get non-zero data. So the zero page should never be > mapped writable to userspace. Check for this condition in > page_table_check_set(). > > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com> > --- > mm/page_table_check.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/page_table_check.c b/mm/page_table_check.c > index e2062748791a..665ece0d55d4 100644 > --- a/mm/page_table_check.c > +++ b/mm/page_table_check.c > @@ -102,6 +102,8 @@ static void page_table_check_set(struct mm_struct *mm, unsigned long addr, > if (!pfn_valid(pfn)) > return; > > + BUG_ON(is_zero_pfn(pfn) && rw); We most probably don't want that: https://lkml.kernel.org/r/20220923113426.52871-2-david@redhat.com
diff --git a/mm/page_table_check.c b/mm/page_table_check.c index e2062748791a..665ece0d55d4 100644 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -102,6 +102,8 @@ static void page_table_check_set(struct mm_struct *mm, unsigned long addr, if (!pfn_valid(pfn)) return; + BUG_ON(is_zero_pfn(pfn) && rw); + page = pfn_to_page(pfn); page_ext = lookup_page_ext(page); anon = PageAnon(page);