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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766262569; bh=3djAmIY/bVZRGmdUxEHr+Zlvw5SAngNGjsGgg06NI6I=; h=From:To:Cc:Subject:Date:From; b=KlzGev4gP45f+/xC+1UTrC3rgFPVQkqGxSimB3iSE6vnu8awn62WEKEfZtumSrnMJ o/RitvRyR7pqNC8ZPX/VhqbpHv9CzTFypt+oOEwsYC+KeUo1wjt6T68RQBihAVL85k 9WNptPhsVsT+6tuBqfZbtpKIikPccd15iqUXcJFu2eRbtUUigMe4JOYlXGF/VUsIx6 cEyN4jNEzFPOy2F5CZi59YcVRR+bO8M+U4VX2shuigZ5IKOYkCmzyRmjf0IFLs5zB7 ldVlqVpm9cVfK/oamhWyOYHTiWfdby5wIujPQ1vSNCMzs5oyTUBU6HpyRzmtJF7g1X 4AdVlTj0+jF9w== From: Sasha Levin To: akpm@linux-foundation.org, david@kernel.org Cc: xu.xin16@zte.com.cn, chengming.zhou@linux.dev, pedrodemargomes@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sasha Levin Subject: [PATCH] mm/ksm: fix pte_unmap_unlock of wrong address in break_ksm_pmd_entry Date: Sat, 20 Dec 2025 15:29:26 -0500 Message-ID: <20251220202926.318366-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 3C7A81A000C X-Rspamd-Server: rspam03 X-Stat-Signature: ueqyku7phxjqb7iqtkoquxa8net8ub1h X-Rspam-User: X-HE-Tag: 1766262571-486923 X-HE-Meta: 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 c+iB3pQs F2vKkVILzqlM+p2G8aKaSfVo3t6YUSaoN8xdIODzaodr2ItQfNPZnXxj5iVbWkNHNocaz006lccdVSqVf8h+yVm2KOQWVU+7QsefzZt30HUQ3PbM01IE3js/UmvF3lZ5Ikghn+8fmjL0mtd2ad0s0efjLrreVOJ50y55qE81Fkd6gYmiwUuEikWLPYZ/0XcL4+aMAhSbJqG55/GbwdDQWvlucUR5Ab/rLHVPY3wQ5dCwuan5S9IvuwQ0UC1a6VZYr/PLYabKxxkfUo2Nae4Qss5VZqA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On ARM32 with HIGHMEM/HIGHPTE, break_ksm_pmd_entry() triggers a BUG during KSM unmerging because pte_unmap_unlock() is passed a pointer that may be beyond the mapped PTE page. The issue occurs when the PTE iteration loop completes without finding a KSM page. After the loop, 'ptep' has been incremented past the last PTE entry. On ARM32 LPAE with 512 PTEs per page (512 * 8 = 4096 bytes), this means ptep points to the next page, outside the kmap'd region. When pte_unmap_unlock(ptep, ptl) calls kunmap_local(ptep), it unmaps the wrong page address, leaving the original kmap slot still mapped. The next kmap_local then finds this slot unexpectedly occupied: WARNING: mm/highmem.c:622 kunmap_local_indexed (address mismatch) kernel BUG at mm/highmem.c:564 __kmap_local_pfn_prot (slot not empty) Fix this by passing start_ptep to pte_unmap_unlock(), which always points within the originally mapped PTE page. Reproducer: Run LTP ksm03 test on ARM32 with HIGHMEM enabled. The test triggers KSM merging followed by unmerging (writing 0 then 2 to /sys/kernel/mm/ksm/run), which exercises break_ksm_pmd_entry(). Fixes: 5d4939fc2258 ("ksm: perform a range-walk in break_ksm") Assisted-by: claude-opus-4-5-20251101 Signed-off-by: Sasha Levin --- mm/ksm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/ksm.c b/mm/ksm.c index cfc182255c7b..2d89a7c8b4eb 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -650,7 +650,7 @@ static int break_ksm_pmd_entry(pmd_t *pmdp, unsigned long addr, unsigned long en } } out_unlock: - pte_unmap_unlock(ptep, ptl); + pte_unmap_unlock(start_ptep, ptl); return found; } -- 2.51.0