From nobody Fri Sep 25 10:39:52 2026 Received: from mxhk.zte.com.cn (mxhk.zte.com.cn [160.30.148.34]) (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 5B3FA371D1D for ; Mon, 14 Sep 2026 08:21:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=160.30.148.34 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789374103; cv=none; b=W+SbKlp9DVJ0KB9DHdwI5EMZ3OxSTNb4tV0tmawmbi/trBoqZhYsAbCtEk6TXSMe4fHtmPloFLUcxtpNohB1RGuVHowBnoGANCMX3tnkPAUh1MdlLWDdl+BUcnRQmWWqXv/dHnx9qb84oLsl3Do/oUi8s5cSTQc/umsi2UW8Pk4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789374103; c=relaxed/simple; bh=4FpH8k3grOvU88n2kU6neA3o39/hf/xYJXr/8JrAAoY=; h=Message-ID:Date:Mime-Version:From:To:Cc:Subject:Content-Type; b=ZdVWA0xybY6Rkz9pHqwDqKwUezxYVBa1N4AWHhvkQ97yPBeM0cQhYrE8VuVIGPbWIfaudS50TJ7ZP3K4OHt0gfzep8jlGqMQcVK9WE0CoMMdt9iLvX3ibIR7eJLY4QWYRPL3jtrpOnX/gFySZBaKj7f8Rh6vuYeTrNlGDalrxXM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zte.com.cn; spf=pass smtp.mailfrom=zte.com.cn; arc=none smtp.client-ip=160.30.148.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zte.com.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zte.com.cn Received: from mse-fl1.zte.com.cn (unknown [10.5.228.132]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mxhk.zte.com.cn (FangMail) with ESMTPS id 4hjymD2zYyz4yjjJ; Mon, 14 Sep 2026 16:21:32 +0800 (CST) Received: from xaxapp04.zte.com.cn ([10.99.98.157]) by mse-fl1.zte.com.cn with SMTP id 68E8LKW7034385; Mon, 14 Sep 2026 16:21:21 +0800 (+08) (envelope-from shao.mingyin@zte.com.cn) Received: from mapi (xaxapp02[null]) by mapi (Zmail) with MAPI id mid32; Mon, 14 Sep 2026 16:21:23 +0800 (CST) X-Zmail-TransId: 2afa6aa7ae83156-d7034 X-Mailer: Zmail v1.0 Message-ID: <20260914162123230u1y1M4UHrO8E-cU-opJ_7@zte.com.cn> Date: Mon, 14 Sep 2026 16:21:23 +0800 (CST) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 From: To: , Cc: , , , , , , , , , Subject: =?UTF-8?B?W1BBVENIIHYzXSByaXNjdjogbGliOiBGaXggWkJCIHN0cm5sZW4gd3JhcC1hcm91bmQgcmVncmVzc2lvbiBvbsKgaHVnZSBjb3VudHM=?= X-MAIL: mse-fl1.zte.com.cn 68E8LKW7034385 X-TLS: YES X-ENVELOPE-SENDER: shao.mingyin@zte.com.cn X-SOURCE-IP: 10.5.228.132 unknown Mon, 14 Sep 2026 16:21:32 +0800 X-CLEAN: YES X-Fangmail-Anti-Spam-Filtered: true X-Fangmail-MID-QID: 6AA7AE8C.000/4hjymD2zYyz4yjjJ Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Shao Mingyin The aligned scan boundary is derived from the last valid byte, (s + count - 1). When count is huge (e.g. SIZE_MAX, which FORTIFY strcat/strlcat pass when the destination size is not known at compile time), s + count wraps around and the boundary lands before s, so the ZBB path returns a bogus length. The original implementation (5ba15d419fab) had the same wrap-around in its (s + count) & ~7 boundary computation; after 5d588c684833 the wrapped boundary is caught by the pre-loop guard "bgeu t0, t4, 2f", which then always exits for aligned strings of 8 or more characters and strnlen() returns 8 instead of the real length. This silently truncates strings built by fortified strcat: the dm sysfs name attribute shows "live-bas" instead of "live-base", the truncated name pollutes the udev database, and blivet/anaconda (as well as LVM/dm-crypt/multipath userspace) break on RISC-V systems. Detect the wrap-around and saturate the boundary to the top of the address space, making the scan equivalent to strlen(). The saturation is branchless (sltu/mask/or), so the normal path does not carry a taken branch. Normal counts are unaffected. Fixes: 5ba15d419fab ("riscv: lib: add strnlen() implementation") Cc: stable@vger.kernel.org Suggested-by: David Laight Signed-off-by: Shao Mingyin Acked-by: Michael Neuling --- Changes in v3: - Replace the taken branch in the saturation with a branchless sltu/mask/or sequence (David Laight). - Update the Clobbers list for the additional t5 register. - Michael's Acked-by is kept: the patch semantics are unchanged, only the saturation sequence is branchless now. Changes in v2: - Point Fixes: at the original implementation (5ba15d419fab) and reword the commit message accordingly: the wrap-around exists since the original implementation, 5d588c684833 only changed how it surfaces (Michael Neuling). - Add Acked-by from Michael Neuling. v2: https://lore.kernel.org/all/20260914145205778-sZJbZc1D-XBfWRXO2f-o@zte.= com.cn/ v1: https://lore.kernel.org/all/20260828145152578tXQPUG9lxxgbJjmfpuaQz@zte.= com.cn/ arch/riscv/lib/strnlen.S | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/arch/riscv/lib/strnlen.S b/arch/riscv/lib/strnlen.S index a8911605c248..528ee7995969 100644 --- a/arch/riscv/lib/strnlen.S +++ b/arch/riscv/lib/strnlen.S @@ -67,7 +67,7 @@ strnlen_zbb: * a1 - Max length of string * * Clobbers - * t0, t1, t2, t3, t4 + * t0, t1, t2, t3, t4, t5 */ /* If maxlen is 0, return 0. */ @@ -87,9 +87,22 @@ strnlen_zbb: * Aligned boundary. Use the address of the last valid byte * (s + count - 1) to avoid loading a word past the count * boundary in the loop below. count =3D=3D 0 is handled above. + * + * Saturate the boundary when s + count wraps around (very large + * counts, e.g. SIZE_MAX passed by FORTIFY strcat/strlcat with a + * destination whose size is unknown at compile time). Without + * this, the wrapped boundary lands before s and the pre-loop + * guard below always exits, returning a truncated length. + * Saturating makes the scan equivalent to strlen(). + * + * Keep the saturation branchless so that the normal path does + * not carry a taken branch that could be mispredicted. */ add t4, a0, a1 addi t4, t4, -1 + sltu t5, t4, a0 /* Did s + count wrap around? */ + sub t5, zero, t5 /* -1 if wrapped, 0 otherwise */ + or t4, t4, t5 /* Saturate to the top of the address space */ andi t4, t4, -SZREG /* Get the first word. */ --=20 2.27.0