[RFC PATCH] arm64: don't vmap() invalid page

[Yury Norov]

On Tue, Jan 18, 2022 at 10:56 AM Matthew Wilcox <willy at infradead.org> wrote:
>
> On Tue, Jan 18, 2022 at 10:53:54AM -0800, Yury Norov wrote:
> > vmap() takes struct page *pages as one of arguments, and user may provide
> > an invalid pointer, which would lead to DABT at address translation later.
> > Currently, kernel checks the pages against NULL. In my case, however, the
> > address was not NULL, and was big enough so that the hardware generated
> > Address Size Abort.
> >
> > Interestingly, this abort happens even if copy_from_kernel_nofault() is used,
> > which is quite inconvenient for debugging purposes.
> >
> > This patch adds an arch_vmap_page_valid() helper into vmap() path, so that
> > architectures may add arch-specific checks of the pointer passed into vmap.
> >
> > For arm64, if the page passed to vmap() corresponds to a physical address
> > greater than maximum possible value as described in TCR_EL1.IPS register, the
> > following table walk would generate Address Size Abort. Instead of creating
> > the invalid mapping, kernel will return ERANGE in such situation.
>
> This seems like a very elaborate way of spelling:
>
>         pfn_valid(page_to_pfn(page));
>
> which doesn't require any architecture hook.  No?

Looks like yes. I'll resend later today if there are no other
comments. Thank you
for the hint.