From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793210746; b=d7acpUU0kwq/i1oH53PtDPOo3oEAVabht7G82twba7/6UrrC12l+7j+PmiKXPkJD3fE+ BQqP7F+Zct/ApU8NqngeGZGi3JYokcnrGhrx29kL8M1RRP0NLDnHvuXXp1depZXvEd0iR Bru7KsxdhGN13qYWjW7qMVnHzBOqqhzypkUQptlTZfjAqQM3IHrTD4SgB16s2DtSZsZBb bc87FpZdi1YtxzIiOKgG5pduNGGPU0m/rfCuVG6WKH6I4G3HeaVD3wVfzwB7sScxp+DWy J+h64hHgHDmSKLBRA0ZAb6W4ngADh8NIqptq96IYUOyPS4NazItN32/1XUG3WEhQMsw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793210746; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=yExc0Il9Reo6gCpt5psJAMXOXesZM4iSWUeDRDCT0z4=; b=KdkSnQgbYmPCdLU4By56Es+mGN22nnyl/yuzJIKQsBNizvZ+FBMHiTH/F1QWc/NUjR2k fgRGnOge0MELn4sq5mXEDKk1NrnUC2lLqEsL27PLxI8Udellj3gsyBeRjye4LPptRobPJ QB0uRHW9ecqqkZ84mIl2WILvesqBw1Vym4UQE1xHv7AzyiNkq2TlyNK1eEjfFI89VwG/T uTplig/RNKEqgWMiCxTOLlH/1WvT0iINELQO8ShJoqJwkr/7/t62npEewx1bgYykOBQaS EvDZ4Xm6Q9KY6P7BcIWqx4vBaygdXOOpfvsVKa966hvDqHSxXeFGUIUuNd0XhuXElAg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=QxXWWXrt; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 86ECE606A31A; Wed, 28 Oct 2026 18:05:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=QxXWWXrt Received: by smtp.kernel.org (Postfix) with ESMTPSA id A05701F01825; Wed, 28 Oct 2026 18:05:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793210746; bh=yExc0Il9Reo6gCpt5psJAMXOXesZM4iSWUeDRDCT0z4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=QxXWWXrt2wZXuPH7bDpnQ2sdUgniivCKLL2F0b0lawlajmcBRFN1WsoLyTZEPPBFF 5IAbiXPQhQJ/2mC1gHL2cbXyN1vfmsFbMGDaPBhWTC9eBs7ub7XScYPaDIHuRz2RY+ jd0daiJ5xGrnQ07TKKStfdj6h2nxUA29LsuapKmU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Karl Mehltretter , Will Deacon , Sasha Levin Subject: [PATCH 5.15 080/571] arm64: mm: Fix the lockless page-table walk in show_pte() Date: Wed, 28 Oct 2026 17:53:47 +0100 Message-ID: <20261028170009.925111657@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170008.009143722@linuxfoundation.org> References: <20261028170008.009143722@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ 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