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b=E2gKdWFh05E+WTUIOy6fVlmJoZ3AvzL3kKF6IpS67NmfM0FfdNGCl0v01yMKbnGC5 gdYwLQP5f3+qFGLh37gfG4MPQtnrkZ/Ly5TzzUuhdbxJEpKQzEOewIjVencSyP5sWg qePR8aIdDUEXfbYtP2RFGB7IRpDpKJR3GnykUJ5p1yZFfcoxDTNJNy80cVP7Zr10ZY o6S9F93N96hliFB9V0GwS0CS0qP5agd9pNj/qum8Hcal7Syo8NGbz0OdNbKfOqpKWA zjROHDvoZF+n5TBVvlruFBx7pLDYILQsS0OoalotCdVlBLjku764siAifLFJzQ/S6M X8q/9FNobYH5A== Date: Mon, 17 Aug 2026 08:51:34 +0300 From: Mike Rapoport To: Kiarash Azarnia Cc: pasha.tatashin@soleen.com, pratyush@kernel.org, graf@amazon.com, kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] kho: fix signed shift UB in kho_preserved_memory_reserve() Message-ID: References: <20260816090038.3117276-1-kiarash.azarnia@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260816090038.3117276-1-kiarash.azarnia@gmail.com> X-Rspam-User: X-Stat-Signature: mgorob51tf69g1p5818ysjeaxe67x77w X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C8111100002 X-HE-Tag: 1786945902-713049 X-HE-Meta: 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 vQaGkrDy YP9MArdTYro/mfzSMzWM0x/eT9QLO9vI3O2w+pex3PbqFawiq465JjF24k6QIgy5qOLn8fITiYz6gFlDQ1ybHI0IH0ooE2jm7Pcy1gERqROvJsoaeWhPWaIu3JkikO0WguGy2yARvVfihzzKJ9zrAXlgBWTYd0Y63ikeEZsWGHzSXBuJmT3+vHxGKQETObYhmktiMwwxJim4B73ATlE/vh9OdG+/Pk3QxLnpVIS/0wRUtoUJ7Z8UxJSdGr/hNPpcdbpwyrEnsn8EGjfLtYwdMPc2KNcsPfK7IC6VSu++oO0Cqr+YqOi1Vzqt+uo9lCBYcK94RGVQedcJQgMmfJq1tsSrpaMx1+yPMzX9tXkjoC6AaHs4Sfh0XbM29oBnqinni8qlGebbkVGmnG0ZMWOyj202W40/eJhxaajSKuQ8arhhraoGB2WN636iGKyG+PWB7M2+LqhfinTPwNFLldGyYubFWL6Fa5vLWX84lWTZCIPbDJ1NIrYAeN5GL84azMDgkYVr0 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Aug 16, 2026 at 12:30:37PM +0330, Kiarash Azarnia wrote: > kho_preserved_memory_reserve() computes the size of a preserved > reservation as: > > sz = 1 << (order + PAGE_SHIFT); > > `1` is a signed int, so the shift is signed-int arithmetic. For order > 19 (a 2 GiB region) it produces 1 << 31, which is unrepresentable in > int and is undefined behavior; in practice it yields 0x80000000, > sign-extended on the assignment to the u64 sz. For order >= 20 the > shift count exceeds the width of int, which is also undefined. The > return value of memblock_reserve() is ignored and memblock_cap_size() > clamps the bogus size, so the kernel silently reserves the wrong > amount of memory for the preserved region. > > kho_alloc_preserve() caps order at MAX_PAGE_ORDER and cannot reach > order 19, but a boot-time reserve_mem= region of at least 2 GiB drives > kho_preserve_pages() to compute order 19, and kho_preserve_pages() is > EXPORT_SYMBOL_GPL(), so the path is reachable. This looks like LLM generated, please make sure to add Assisted-by tag next time. > Cast the shift operand to u64 so the arithmetic is done in 64 bits: > > sz = (u64)1 << (order + PAGE_SHIFT); > > Fixes: 3f2ad90060f6 ("kho: adopt radix tree for preserved memory tracking") > Cc: stable@vger.kernel.org > Signed-off-by: Kiarash Azarnia > --- > kernel/liveupdate/kexec_handover.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > index 175c08a6e41e..c79f48bd64ac 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -501,7 +501,7 @@ static int __init kho_preserved_memory_reserve(phys_addr_t phys, > struct page *page; > u64 sz; > > - sz = 1 << (order + PAGE_SHIFT); > + sz = (u64)1 << (order + PAGE_SHIFT); > page = kho_get_preserved_page(phys, order); This is already fixed: https://patch.msgid.link/20260727150240.889555-1-pratyush@kernel.org > /* Reserve the memory preserved in KHO in memblock */ > -- > 2.53.0 > -- Sincerely yours, Mike.