Re: [PATCH] mm,memblock: reset memblock.reserved to system init state to prevent UAF

[Rik van Riel]

On Thu, 2023-07-20 at 08:00 +0300, Mike Rapoport wrote:
> Hi Ric,
> 
> On Wed, Jul 19, 2023 at 03:41:37PM -0400, Rik van Riel wrote:
> > The memblock_discard function frees the memblock.reserved.regions
> > array, which is good.
> > 
> > However, if a subsequent memblock_free (or memblock_phys_free)
> > comes
> > in later, from for example ima_free_kexec_buffer, that will result
> > in
> > a use after free bug in memblock_isolate_range.
> 
> The use of memblock_phys_free() in ima_free_kexec_buffer() is
> entirely
> bogus and must be fixed. It should be memblock_free_late() there.
> 
I'll send in a patch for that code, then. Thank you!

> > When running a kernel with CONFIG_KASAN enabled, this will cause a
> > kernel panic very early in boot. Without CONFIG_KASAN, there is
> > a chance that memblock_isolate_range might scribble on memory
> > that is now in use by somebody else.
>  
> This can't happen because memblock_double_array() uses kmalloc() as
> soon as
> slab_is_available(), so this sentence is misleading.

memblock_discard() freed the array, but did not change
the pointer. That resulted in memblock_isolate_range()
following a stale pointer.

There was no call to memblock_double_array() in the
final call that crashed. I checked that by booting
with memblock=debug.

kind regards,

Rik van Riel
-- 
All Rights Reversed.

Attachment: signature.asc
Description: This is a digitally signed message part