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Sun, 16 Aug 2026 02:25:35 -0700 (PDT) Received: from zen ([37.203.152.61]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49996176b8asm27309575e9.11.2026.08.16.02.25.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 16 Aug 2026 02:25:35 -0700 (PDT) From: Kiarash Azarnia To: rppt@kernel.org, pasha.tatashin@soleen.com, pratyush@kernel.org Cc: graf@amazon.com, kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] kho: fix signed shift UB in kho_preserved_memory_reserve() Date: Sun, 16 Aug 2026 12:55:34 +0330 Message-ID: <20260816092534.3333563-1-kiarash.azarnia@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260816090038.3117276-1-kiarash.azarnia@gmail.com> References: <20260816090038.3117276-1-kiarash.azarnia@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260816_022537_453114_17A784C6 X-CRM114-Status: UNSURE ( 6.25 ) X-CRM114-Notice: Please train this message. X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org Here is how I reproduced this, in case it is useful for review. Minimal reproducer (prints what the function computes, both ways): #include #define PAGE_SHIFT 12 int main(void) { int order; for (order = 18; order <= 20; order++) { unsigned long long before = 1 << (order + PAGE_SHIFT); unsigned long long after = (unsigned long long)1 << (order + PAGE_SHIFT); printf("order=%2d before=0x%llx after=0x%llx\n", order, before, after); } return 0; } prints: order=18 before=0x40000000 after=0x40000000 order=19 before=0xffffffff80000000 after=0x80000000 order=20 before=0x1 after=0x100000000 Order 19 is a 2 GiB region, reachable from a reserve_mem=2G boot. It also shows on a real boot: with CONFIG_KEXEC_HANDOVER=y, CONFIG_LIVEUPDATE=y, CONFIG_UBSAN unset, and reserve_mem=2G:2G:khotest kho_scratch=128M,128M,128M kho=on liveupdate=on kexec -l -s --reuse-cmdline --append=" luo_stage=2" stage 2 warned in memblock_add_range and lost ~820 MB (MemTotal 5181908 kB vs 6004928 kB in stage 1); after the fix, no WARN, MemTotal 6004884 kB.