Subject: [PATCH] arm64: dump: hide kernel pointers

From: [email-masked] (Mark Rutland)
Date: Tue, 28 Feb 2017 10:04:20 +0000

On Tue, Feb 28, 2017 at 08:42:51AM +0000, Ard Biesheuvel wrote:
> (+ Mark)

(+ Laura)

> On 28 February 2017 at 07:05, Miles Chen <[email-masked]> wrote:
> > Mask kernel pointers of /sys/kernel/debug/kernel_page_tables entry like
> > /proc/vmallocinfo does.
> >
> > With sysctl kernel.kptr_restrict=0 or 1:
> > cat /sys/kernel/debug/kernel_page_tables
> 
> I wonder if this file should be accessible at all if kptr_restrict > 0

I don't have strong feelings either way.

This isn't typically enabled, and it's under debugfs, so this shouldn't
be accessible by a typical user anyhow.

That said, there are very few of us who need to take a look at this
file. I'm happy to deal with attacking kptr_restrict when required.

Thanks,
Mark.

> > ---[ Modules start ]---
> > ---[ Modules end ]---
> > ---[ vmalloc() Area ]---
> > ffffff8008000000-ffffff8008010000          64K PTE       RW NX SHD AF...
> > ffffff8008015000-ffffff8008016000           4K PTE       RW NX SHD AF...
> > ffffff8008020000-ffffff8008030000          64K PTE       RW NX SHD AF...
> > ffffff8008031000-ffffff8008071000         256K PTE       RW NX SHD AF...
> > ffffff8008080000-ffffff8008200000        1536K PTE       ro x  SHD AF...
> > ffffff8008200000-ffffff8008400000           2M PMD       ro x  SHD AF...
> > ffffff8008400000-ffffff8008540000        1280K PTE       ro x  SHD AF...
> > ffffff8008540000-ffffff8008690000        1344K PTE       ro NX SHD AF...
> > ffffff8008940000-ffffff8008a10000         832K PTE       RW NX SHD AF...
> > ffffff8008aca000-ffffff8008acd000          12K PTE       RW NX SHD AF...
> > ffffffbebffd8000-ffffffbebffdb000          12K PTE       RW NX SHD AF...
> > ---[ vmalloc() End ]---
> > ---[ Fixmap start ]---
> > ffffffbefe800000-ffffffbefea00000           2M PMD       ro NX SHD AF...
> > ---[ Fixmap end ]---
> > ---[ PCI I/O start ]---
> > ---[ PCI I/O end ]---
> > ---[ Linear Mapping ]---
> > ffffffc000000000-ffffffc000080000         512K PTE       RW NX SHD AF...
> > ffffffc000080000-ffffffc000200000        1536K PTE       ro NX SHD AF...
> > ffffffc000200000-ffffffc000600000           4M PMD       ro NX SHD AF...
> > ffffffc000600000-ffffffc000690000         576K PTE       ro NX SHD AF...
> > ffffffc000690000-ffffffc000800000        1472K PTE       RW NX SHD AF...
> > ffffffc000800000-ffffffc002000000          24M PMD       RW NX SHD AF...
> > ffffffc002000000-ffffffc040000000         992M PMD       RW NX SHD AF...
> > ffffffc040000000-ffffffc080000000           1G PGD       RW NX SHD AF...
> >
> > With sysctl kernel.kptr_restrict=2:
> > cat /sys/kernel/debug/kernel_page_tables
> > ---[ Modules start ]---
> > ---[ Modules end ]---
> > ---[ vmalloc() Area ]---
> > 0000000000000000-0000000000000000          64K PTE       RW NX SHD AF...
> > 0000000000000000-0000000000000000           4K PTE       RW NX SHD AF...
> > 0000000000000000-0000000000000000          64K PTE       RW NX SHD AF...
> > 0000000000000000-0000000000000000         256K PTE       RW NX SHD AF...
> > 0000000000000000-0000000000000000        1536K PTE       ro x  SHD AF...
> > 0000000000000000-0000000000000000           2M PMD       ro x  SHD AF...
> > 0000000000000000-0000000000000000        1280K PTE       ro x  SHD AF...
> > 0000000000000000-0000000000000000        1344K PTE       ro NX SHD AF...
> > 0000000000000000-0000000000000000         832K PTE       RW NX SHD AF...
> > 0000000000000000-0000000000000000          12K PTE       RW NX SHD AF...
> > 0000000000000000-0000000000000000          12K PTE       RW NX SHD AF...
> > ---[ vmalloc() End ]---
> > ---[ Fixmap start ]---
> > 0000000000000000-0000000000000000           2M PMD       ro NX SHD AF...
> > ---[ Fixmap end ]---
> > ---[ PCI I/O start ]---
> > ---[ PCI I/O end ]---
> > ---[ Linear Mapping ]---
> > 0000000000000000-0000000000000000         512K PTE       RW NX SHD AF...
> > 0000000000000000-0000000000000000        1536K PTE       ro NX SHD AF...
> > 0000000000000000-0000000000000000           4M PMD       ro NX SHD AF...
> > 0000000000000000-0000000000000000         576K PTE       ro NX SHD AF...
> > 0000000000000000-0000000000000000        1472K PTE       RW NX SHD AF...
> > 0000000000000000-0000000000000000          24M PMD       RW NX SHD AF...
> > 0000000000000000-0000000000000000         992M PMD       RW NX SHD AF...
> > 0000000000000000-0000000000000000           1G PGD       RW NX SHD AF...
> >
> > Signed-off-by: Miles Chen <[email-masked]>
> > ---
> >  arch/arm64/mm/dump.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
> > index ca74a2a..e055ecf 100644
> > --- a/arch/arm64/mm/dump.c
> > +++ b/arch/arm64/mm/dump.c
> > @@ -253,8 +253,8 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned level,
> >                 if (st->current_prot) {
> >                         note_prot_uxn(st, addr);
> >                         note_prot_wx(st, addr);
> > -                       pt_dump_seq_printf(st->seq, "0x%016lx-0x%016lx   ",
> > -                                  st->start_address, addr);
> > +                       pt_dump_seq_printf(st->seq, "%pK-%pK   ",
> > +                                  (void *)st->start_address, (void *)addr);
> >
> >                         delta = (addr - st->start_address) >> 10;
> >                         while (!(delta & 1023) && unit[1]) {
> > --
> > 1.9.1
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel