From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 23ECC197A76 for ; Thu, 25 Jul 2024 09:03:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721898232; cv=none; b=SA9unSrg4isXu9o3r7yS3WEqfTEkoo3fqbv6HnRzHuX1ojgLuvaAxxNUQZlfPE0D7xKbJwzS4RK68E1Rc6t2HGx8VyHYvHeiM/FHDQ4VrlcMOeDP5G+s2sz5FJzGPH/OOA18048jQwep3q/S5AKma5SlRMwLkMRcJAHIWX9INzc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721898232; c=relaxed/simple; bh=ktq7M3foSa4aHhEmT7CQctdVVEd8++vnRRMJLYqAi+A=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=tnhBuqJnzHsSgNj/kwlOq/fU471iFFKLO0DVEoaW7a0QBA3OiDeGvElQE2hCBWAeoBdEnCmVRcuSSq/ljRqyX4tB3RZGF9nPNHU3WOptai65klCoTl1+hw0KoHyRYWH3fPxUNMm7i8Vjp02P3S7dz1q/NL/6V616TXC2pMCIygE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ey08YAgW; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ey08YAgW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C80AC32786; Thu, 25 Jul 2024 09:03:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721898231; bh=ktq7M3foSa4aHhEmT7CQctdVVEd8++vnRRMJLYqAi+A=; h=From:To:Cc:Subject:Date:From; b=ey08YAgWZlA+LDmC0EVMst7itd4EbUyEmIxbMcRw1XcZmSE+klIO6UOZV3jRJOTGV w1a2+BJBRE8X/iEX7wkJkyXe2dJpVymNUAnmeXzIlhUgevIM5nYznmwwMnM87+wjeW WL4vOSR1ECpCeylnwJaZvIFA+u7lNLzTZdg1tznZKRjF61WNRT/DHtJMgUhuENxiEK 6ebv555mTHnaGJ30K230oG2hfjqmSnMb7WgzEuIAXMHEqbeHuEFNMDk1suLBn3tOAc spsPBWUI6IfPOEKGazox3iTdipDapJfhq6MxMFx1gxXEadnydn+EsDsDhxQKrljWWD jdmEVjJDzqdKw== From: Will Deacon To: linux-arm-kernel@lists.infradead.org Cc: Will Deacon , Catalin Marinas , Ard Biesheuvel , stable@vger.kernel.org, Asahi Lina Subject: [PATCH] arm64: mm: Fix lockless walks with static and dynamic page-table folding Date: Thu, 25 Jul 2024 10:03:45 +0100 Message-Id: <20240725090345.28461-1-will@kernel.org> X-Mailer: git-send-email 2.20.1 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Lina reports random oopsen originating from the fast GUP code when 16K pages are used with 4-level page-tables, the fourth level being folded at runtime due to lack of LPA2. In this configuration, the generic implementation of p4d_offset_lockless() will return a 'p4d_t *' corresponding to the 'pgd_t' allocated on the stack of the caller, gup_fast_pgd_range(). This is normally fine, but when the fourth level of page-table is folded at runtime, pud_offset_lockless() will offset from the address of the 'p4d_t' to calculate the address of the PUD in the same page-table page. This results in a stray stack read when the 'p4d_t' has been allocated on the stack and can send the walker into the weeds. Fix the problem by providing our own definition of p4d_offset_lockless() when CONFIG_PGTABLE_LEVELS <= 4 which returns the real page-table pointer rather than the address of the local stack variable. Cc: Catalin Marinas Cc: Ard Biesheuvel Cc: Link: https://lore.kernel.org/r/50360968-13fb-4e6f-8f52-1725b3177215@asahilina.net Fixes: 0dd4f60a2c76 ("arm64: mm: Add support for folding PUDs at runtime") Reported-by: Asahi Lina Signed-off-by: Will Deacon --- arch/arm64/include/asm/pgtable.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index f8efbc128446..7a4f5604be3f 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1065,6 +1065,28 @@ static inline bool pgtable_l5_enabled(void) { return false; } #define p4d_offset_kimg(dir,addr) ((p4d_t *)dir) +static inline +p4d_t *p4d_offset_lockless_folded(pgd_t *pgdp, pgd_t pgd, unsigned long addr) +{ + /* + * With runtime folding of the pud, pud_offset_lockless() passes + * the 'pgd_t *' we return here to p4d_to_folded_pud(), which + * will offset the pointer assuming that it points into + * a page-table page. However, the fast GUP path passes us a + * pgd_t allocated on the stack and so we must use the original + * pointer in 'pgdp' to construct the p4d pointer instead of + * using the generic p4d_offset_lockless() implementation. + * + * Note: reusing the original pointer means that we may + * dereference the same (live) page-table entry multiple times. + * This is safe because it is still only loaded once in the + * context of each level and the CPU guarantees same-address + * read-after-read ordering. + */ + return p4d_offset(pgdp, addr); +} +#define p4d_offset_lockless p4d_offset_lockless_folded + #endif /* CONFIG_PGTABLE_LEVELS > 4 */ #define pgd_ERROR(e) \ -- 2.45.2.1089.g2a221341d9-goog