From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E2ECD58F066 for ; Thu, 10 Sep 2026 19:08:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789067325; cv=none; b=BjI8WvsNb4xp/FVEVMtcJCCNQKwKNGBYTHM9sLYfzAYL17flIOz+8VuPRdQ1+bzTCBJKQZ5r8FeW+izxd+ZgJCn0vcDDtGQWBhy2tzu14fCXyqwoDzWnRg/2u8k3o62ZI9blUIS5XSzu8y857CbGgUIW1+up9uOWzB6g4EoOXZ8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789067325; c=relaxed/simple; bh=RiPsCQPituENL53gccxkXUYYXp7BHFy5sxzaHNDbXRg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UMBZZlpzm8M/rtJ8XsnItfgw1ZA/u7PaZ7iedaf7sHXo08/ZGd0i8lPVncTdyBa+ZZpW0KJ6xjVc+08cy+IYD2YmDwh00KDo8B5+bC1Kf45nAnodFWSX4BL46YHslJ8Vi17p+9ATO1dExJEE2DWGdmDijVsR/hrKHNxPbEB7gFM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fhD2aXGZ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fhD2aXGZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13A7E1F00898; Thu, 10 Sep 2026 19:08:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789067323; bh=q/gk/YpLPeRqTFdCdODsQWsh+oCQnScR+9+xqn9RSHY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=fhD2aXGZdFncJl5o2HvL85bDWMWV5eOTjO1HLmgJUq6qMu/TOlLmDoD3VYQvFFT/s wiqQ+T2AsfDJd8hqOqmZZX2p5T74mYaT19Kq/ZT9ovRjVYDsFO3qxc6yo+xyrGUuvT fku+VeiL1NDgxgIm2J9vb4ffxNsrdjBRFIScBBHaw1HTOQ+DVG7RP4Tnz6qtlfnukD eAPJLBaBwZNwjXXFU5hwbJ7IxGHFibYnUYMgrEnRFPsqVsxvSX/w4Et44/1KpfEMz3 SifdumPyijvQWdIraw+n7Jtn6V/RwY+2uQBGgwVyeEQSEtnoIiqZPeZItoouGXcDmm rb1eff7J96URA== From: Sasha Levin To: stable@vger.kernel.org Cc: Karl Mehltretter , Will Deacon , Sasha Levin Subject: [PATCH 5.15.y 2/2] arm64: mm: Fix the lockless page-table walk in show_pte() Date: Thu, 10 Sep 2026 15:08:37 -0400 Message-ID: <20260910190837.1453363-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260910190837.1453363-1-sashal@kernel.org> References: <2026090941-average-edition-4184@gregkh> <20260910190837.1453363-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Karl Mehltretter [ Upstream commit a77644d009dece1104b6fcc6e322b0e4503db0d6 ] show_pte() walks page tables locklessly and can run with interrupts enabled. A concurrent teardown can free a table page while it is being walked. It can also clear a parent entry after show_pte() checked it; the regular pXd_offset() helpers then reread the cleared entry and can derive a bogus lower-level pointer and fault again. Use the lockless offset helpers with the saved parent entries, as gup_fast() does, and pass the saved PMD to pte_offset_map(). For task page tables, arm64 selects MMU_GATHER_RCU_TABLE_FREE. Disable local interrupts around the walk to hold off RCU-deferred table frees and block the tlb_remove_table_sync_one() IPI until the walk is finished. Place the IRQ guard after the header print. This does not make the output a consistent snapshot, but prevents the task page-table walk from dereferencing a released table page or deriving a pointer from a different parent value. Fixes: 1d18c47c735e ("arm64: MMU fault handling and page table management") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Karl Mehltretter Signed-off-by: Will Deacon [ replaced guard(irqsave)() with explicit local_irq_save()/local_irq_restore() calls to avoid declarations after statements. ] Signed-off-by: Sasha Levin --- arch/arm64/mm/fault.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 39f03d18717eb..0155330b9d0da 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include #include @@ -123,6 +124,7 @@ static void show_pte(unsigned long addr) struct mm_struct *mm; pgd_t *pgdp; pgd_t pgd; + unsigned long flags; if (is_ttbr0_addr(addr)) { /* TTBR0 */ @@ -144,6 +146,9 @@ static void show_pte(unsigned long addr) pr_alert("%s pgtable: %luk pages, %llu-bit VAs, pgdp=%016lx\n", mm == &init_mm ? "swapper" : "user", PAGE_SIZE / SZ_1K, vabits_actual, mm_to_pgd_phys(mm)); + + local_irq_save(flags); + pgdp = pgd_offset(mm, addr); pgd = READ_ONCE(*pgdp); pr_alert("[%016lx] pgd=%016llx", addr, pgd_val(pgd)); @@ -157,25 +162,25 @@ static void show_pte(unsigned long addr) if (pgd_none(pgd) || pgd_bad(pgd)) break; - p4dp = p4d_offset(pgdp, addr); + p4dp = p4d_offset_lockless(pgdp, pgd, addr); p4d = READ_ONCE(*p4dp); pr_cont(", p4d=%016llx", p4d_val(p4d)); if (p4d_none(p4d) || p4d_bad(p4d)) break; - pudp = pud_offset(p4dp, addr); + pudp = pud_offset_lockless(p4dp, p4d, addr); pud = READ_ONCE(*pudp); pr_cont(", pud=%016llx", pud_val(pud)); if (pud_none(pud) || pud_bad(pud)) break; - pmdp = pmd_offset(pudp, addr); + pmdp = pmd_offset_lockless(pudp, pud, addr); pmd = READ_ONCE(*pmdp); pr_cont(", pmd=%016llx", pmd_val(pmd)); if (pmd_none(pmd) || pmd_bad(pmd)) break; - ptep = pte_offset_map(pmdp, addr); + ptep = pte_offset_map(&pmd, addr); if (!ptep) break; @@ -185,6 +190,7 @@ static void show_pte(unsigned long addr) } while(0); pr_cont("\n"); + local_irq_restore(flags); } /* -- 2.53.0