From: Andrew Morton <akpm@linux-foundation.org>
To: Marco Elver <elver@google.com>
Cc: Alexander Graf <graf@amazon.com>, Mike Rapoport <rppt@kernel.org>,
Pasha Tatashin <pasha.tatashin@soleen.com>,
Pratyush Yadav <pratyush@kernel.org>,
kexec@lists.infradead.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com
Subject: Re: [PATCH v2] kho: use checked arithmetic in deserialize_bitmap()
Date: Thu, 19 Mar 2026 19:37:35 -0700 [thread overview]
Message-ID: <20260319193735.2ea34594b36d37e7850a8c37@linux-foundation.org> (raw)
In-Reply-To: <20260319210528.1694513-2-elver@google.com>
On Thu, 19 Mar 2026 22:03:53 +0100 Marco Elver <elver@google.com> wrote:
> The function deserialize_bitmap() calculates the reservation size using:
>
> int sz = 1 << (order + PAGE_SHIFT);
>
> If a corrupted KHO image provides an order >= 20 (on systems with 4KB
> pages), the shift amount becomes >= 32, which overflows the 32-bit
> integer. This results in a zero-size memory reservation.
>
> Furthermore, the physical address calculation:
>
> phys_addr_t phys = elm->phys_start + (bit << (order + PAGE_SHIFT));
>
> can also overflow and wrap around if the order is large. This allows a
> corrupt KHO image to cause out-of-bounds updates to page->private of
> arbitrary physical pages during early boot.
>
> Fix this by changing 'sz' to 'unsigned long' and using checked add and
> shift to safely calculate the shift amount, size, and physical address,
> skipping malformed chunks. This allows preserving memory with an order
> larger than MAX_PAGE_ORDER.
AI review asked questions:
https://sashiko.dev/#/patchset/20260319210528.1694513-2-elver%40google.com
next prev parent reply other threads:[~2026-03-20 2:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-19 21:03 Marco Elver
2026-03-20 2:37 ` Andrew Morton [this message]
2026-03-20 9:34 ` Pratyush Yadav
2026-03-20 8:56 ` Pratyush Yadav
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