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b=IwWduJK3Q0ps7Q3T+6/cPljz9bzlzMD7YqehSZQMUvmFFsKNNaEaT95LdBmvO9GZ+ lfFcqCjV8DbrRsRL9Ejn3CjOPulO8Hz7jBmzM6QLuIdqFibLx3wFc/nlIqvK8ftg5i m/tEnf74BYEjDiRWWfvBLfYs2Qa/MhZdCaz++kKi75vnjLKGmYep338ZfTx5cAa3dk VHR21V/T9FAgHlP3jIcO9L7mmeBt9rTSotZmIfD7CN+FQH0+tEG8pVuIivy2p6BrB/ EmW9cbnzzY4hTZCmlQhlrmLpYqdTu6BZ9aEzMIyAl0fxpaL6QV1Wd2lyyDxPBmUQVG jVPTvbJrZeGBA== From: Pratyush Yadav To: Marco Elver Cc: Alexander Graf , Mike Rapoport , Pasha Tatashin , Pratyush Yadav , 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() In-Reply-To: <20260319210528.1694513-2-elver@google.com> (Marco Elver's message of "Thu, 19 Mar 2026 22:03:53 +0100") References: <20260319210528.1694513-2-elver@google.com> Date: Fri, 20 Mar 2026 08:56:34 +0000 Message-ID: <2vxzzf42c20t.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Stat-Signature: mm5j9shp5jg361k3a6baqzsotb817rgu X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: 6417FA0005 X-HE-Tag: 1773996999-470429 X-HE-Meta: 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 SoY5RM2B A/REu2KJCKnK/pDm7vRdv5n/xH2KvjyJ+lZ5gW39VHM8zLcT9WzBF0lQBaiQea/9xbw/zrkvBdE50ZP+Az36RNS7wNTeYlx7Ob0Fban5nAmADr6h1ALNDadQMPRTeS09n+EUvgVBog6KBrQl8MnbuOmw6axeVAjvQpevRuokeZr6PhY+RMsEPkXwmOR/frmjS1954iUhcoDl2iHG+9g7N25PYGZJ3pfgOfWV9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Marco, On Thu, Mar 19 2026, Marco Elver 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. > > Fixes: fc33e4b44b27 ("kexec: enable KHO support for memory preservation") > Signed-off-by: Marco Elver deserialize_bitmap() is replaced with the radix tree with this series [0]. Can you please redo these changes on top of that? Also, a couple comments below. [0] https://lore.kernel.org/linux-mm/20260206021428.3386442-1-jasonmiu@google.com/ > --- > v2: > * Switch to unsigned long and use checked shift and add (Mike). > > v1: https://lore.kernel.org/all/20260214010013.3027519-1-elver@google.com/ > --- > kernel/liveupdate/kexec_handover.c | 23 +++++++++++++++++++---- > 1 file changed, 19 insertions(+), 4 deletions(-) > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > index cc68a3692905..0d8417dcd3ff 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -19,6 +19,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -461,15 +462,29 @@ static void __init deserialize_bitmap(unsigned int order, > struct khoser_mem_bitmap_ptr *elm) > { > struct kho_mem_phys_bits *bitmap = KHOSER_LOAD_PTR(elm->bitmap); > + unsigned int shift; > unsigned long bit; > + unsigned long sz; > + > + if (check_add_overflow(order, PAGE_SHIFT, &shift) || > + check_shl_overflow(1UL, shift, &sz)) { > + pr_warn("invalid order %u for preserved bitmap\n", order); > + return; > + } Isn't it simpler to just check if (order + PAGE_SHIFT) > 63? KHO is only designed to work on 64-bit platforms so we know the max possible shift already. Is there any reason to call the proper overflow functions? The only reason I ask is because I find the open-coded check easier to read. > > for_each_set_bit(bit, bitmap->preserve, PRESERVE_BITS) { > - int sz = 1 << (order + PAGE_SHIFT); > - phys_addr_t phys = > - elm->phys_start + (bit << (order + PAGE_SHIFT)); > - struct page *page = phys_to_page(phys); > + phys_addr_t offset, phys; > + struct page *page; > union kho_page_info info; > > + if (check_shl_overflow((phys_addr_t)bit, shift, &offset) || > + check_add_overflow(elm->phys_start, offset, &phys)) { > + pr_warn("invalid phys layout for preserved bitmap\n"); > + return; > + } > + > + page = phys_to_page(phys); > + > memblock_reserve(phys, sz); > memblock_reserved_mark_noinit(phys, sz); > info.magic = KHO_PAGE_MAGIC; -- Regards, Pratyush Yadav