Re: [PATCH 1/1] ACPI: fix acpi table use after free

["Rafael J. Wysocki" <rafael@kernel.org>]

On Sat, Mar 20, 2021 at 9:25 AM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Thu, Mar 18, 2021 at 04:22:37PM +0100, Rafael J. Wysocki wrote:
> > On Thu, Mar 18, 2021 at 11:50 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > >
> > > On Thu, Mar 18, 2021 at 8:25 AM Mike Rapoport <rppt@linux.ibm.com> wrote:
> > > >
> > > > On Wed, Mar 17, 2021 at 09:14:37PM +0100, Rafael J. Wysocki wrote:
> > > > > On Monday, March 15, 2021 5:19:29 PM CET Rafael J. Wysocki wrote:
> > > > > > On Sun, Mar 14, 2021 at 8:00 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> > > > > > >
> > > > > > > On Thu, Mar 11, 2021 at 04:36:31PM +0100, Rafael J. Wysocki wrote:
> > > > > > > > On Wed, Mar 10, 2021 at 8:47 PM David Hildenbrand <david@redhat.com> wrote:
> > > > > > > > > >
> > > > > > > > > > There is some care that should be taken to make sure we get the order
> > > > > > > > > > right, but I don't see a fundamental issue here.
> > > > > > > >
> > > > > > > > Me neither.
> > > > > > > >
> > > > > > > > > > If I understand correctly, Rafael's concern is about changing the parts of
> > > > > > > > > > ACPICA that should be OS agnostic, so I think we just need another place to
> > > > > > > > > > call memblock_reserve() rather than acpi_tb_install_table_with_override().
> > > > > > > >
> > > > > > > > Something like this.
> > > > > > > >
> > > > > > > > There is also the problem that memblock_reserve() needs to be called
> > > > > > > > for all of the tables early enough, which will require some reordering
> > > > > > > > of the early init code.
> > > > > > > >
> > > > > > > > > > Since the reservation should be done early in x86::setup_arch() (and
> > > > > > > > > > probably in arm64::setup_arch()) we might just have a function that parses
> > > > > > > > > > table headers and reserves them, similarly to how we parse the tables
> > > > > > > > > > during KASLR setup.
> > > > > > > >
> > > > > > > > Right.
> > > > > > >
> > > > > > > I've looked at it a bit more and we do something like the patch below that
> > > > > > > nearly duplicates acpi_tb_parse_root_table() which is not very nice.
> > > > > >
> > > > > > It looks to me that the code need not be duplicated (see below).
> > > > > >
> > > > > > > Besides, reserving ACPI tables early and then calling acpi_table_init()
> > > > > > > (and acpi_tb_parse_root_table() again would mean doing the dance with
> > > > > > > early_memremap() twice for no good reason.
> > > > > >
> > > > > > That'd be simply inefficient which is kind of acceptable to me to start with.
> > > > > >
> > > > > > And I changing the ACPICA code can be avoided at least initially, it
> > > > > > by itself would be a good enough reason.
> > > > > >
> > > > > > > I believe the most effective way to deal with this would be to have a
> > > > > > > function that does parsing, reservation and installs the tables supplied by
> > > > > > > the firmware which can be called really early and then another function
> > > > > > > that overrides tables if needed a some later point.
> > > > > >
> > > > > > I agree that this should be the direction to go into.
> > > > >
> > > > > So maybe something like the patch below?
> > > > >
> > > > > I'm not sure if acpi_boot_table_prepare() gets called early enough, though.
> > > >
> > > > To be 100% safe it should be called before e820__memblock_setup().
> > >
> > > OK
> >
> > Well, that said, reserve_bios_regions() doesn't seem to have concerns
> > like this and I'm not sure why ACPI tables should be reserved before
> > this runs.  That applies to efi_reserve_boot_services() too.
> >
> > I can put the new call before e820__memblock_alloc_reserved_mpc_new(),
> > but I'm not sure why to put it before efi_reserve_boot_services(),
> > say?
>
> The general idea is to reserve all the memory used by the firmware before
> memblock allocations are possible, i.e. before e820__memblock_setup().
> Currently this is not the case, but it does not make it more correct.

I see.

> Theoretically, it is possible that reserve_bios_regions() will cause a
> memory allocation and the allocated memory will be exactly at the area
> where ACPI tables reside.
>
> In practice I believe this is very unlikely, but who knows.
>
> Another advantage of having ACPI tables handy by the time we do the memory
> detection is that we will be able to SRAT earlier and simplify NUMA
> initialization.

OK, fair enough.