From nobody Wed Feb 11 10:54:29 2026 Received: from mail-pl1-f170.google.com (mail-pl1-f170.google.com [209.85.214.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3056416FF30 for ; Sat, 9 Mar 2024 20:24:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710015893; cv=none; b=vEcGxsPMQpwHMcZsoF9+By9mQ/hEPbzHDBEMNjKB5L5UyeO3/XFvvMujeDUMmfETSd/28yG0NAuaSw7qdp1FsEVRv7ZgfRIZJccW+GktBz/OtlFbx1RIQD0gjL0UkkZyVMguRMsah13kH0wfv02UcB5xsgneqgsSZszJ6NBH3wM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710015893; c=relaxed/simple; bh=K9RoT73X71QnB+uU8sWtSEx1Mtsrf1E5zhfyiv3p1ZE=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=DTvy3KzbtTw5fJ7mraJIwpaPZSgK32ikbhcTotQb1vzuzoVzpYLq/hnmO0ECCT0gvbaN8uH2rAu6cC1BEgkE2FXvQVWLdkP16ztjgVQ0TK8Q2imDkQeCcf/hl7QZO4xH/23wcWBhsMgwkKKb6VOvDMmqTWl4RLzamv3MaYFMkFg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=chromium.org; spf=pass smtp.mailfrom=chromium.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b=YX3h28jB; arc=none smtp.client-ip=209.85.214.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=chromium.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=chromium.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="YX3h28jB" Received: by mail-pl1-f170.google.com with SMTP id d9443c01a7336-1dd10ae77d8so26162875ad.0 for ; Sat, 09 Mar 2024 12:24:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1710015891; x=1710620691; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=pzdoSSC7M3Gn4nXch6enCVEFVBAir+v+I5+bn35uJJU=; b=YX3h28jB4WRGi8wJ7maxuIUdu3IA/SyxGwsGyKSysTuUxqt4RdCWISSRKrBb73+omm 8LrXJU8Q152eXWTVi2ap6yN+wg1jxk38dZHEfU/1xDUPkdqEwEyCqBHFVAoO1FrqnZbv ccDXNWMXlkJiG1ACdvW+Ay71rFBL8lSPTFkr8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1710015891; x=1710620691; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=pzdoSSC7M3Gn4nXch6enCVEFVBAir+v+I5+bn35uJJU=; b=HCUT6KTpknH73hzc/ie3XORFRtTXs4Es8mYYl+FXNXRW2iD72ReJq2tnZCaSlDw8Jd 4hS3ZIfyD1jpQFwws+jG5b5jKFyOWgCvvSiNa+LABAvXiV/rfBwSA6vqmtfuDq7QZ7KQ ySjHjEJzRX3F9hwh4Ec99241ijOR4G/7Zl3UUR3hbVCOrOcTy7stny7RKZEl6zalt6Mz kyq0DDoIaMsFf7l4O+Ef26Rv90EuI1bUHExoC3eAbv1sfqbIwSLxwC/NTnU4yP5Zs52C 4CNzV8JCvV5Pu4YXoWq615QC3nldREcUUJPpo4SOLK45Ve8ezaFcjHAl42IoEQC0jpsM 2HRQ== X-Forwarded-Encrypted: i=1; AJvYcCWkJh9PyktQN+e99MTalg5ECOYVt3KkeB1hNOWcTUcbD5aw+0d6qOilAidiBGEglYa9mrjEnw8vCJ/ncs2+S70mpTjQweKCCvOmhNfO X-Gm-Message-State: AOJu0YymHyVOqNPVdw/T5IyG6h7hPDinsQU8Cis+jSPIaa78cgjetaPp IIZghkW1Ealq4jn4DGRVruQ/XdYaiHdf3xBZASJl6G6ahNlbjETQ1XIqvaKjag== X-Google-Smtp-Source: AGHT+IHS3V/gDLEjjvi9Itvln/GKgAbneox6bx5epnt2P+RSO7WF1SQOAKdmHYGasuxFgTMM+KSrxg== X-Received: by 2002:a17:902:ee51:b0:1dc:abf0:14ee with SMTP id 17-20020a170902ee5100b001dcabf014eemr1783343plo.22.1710015891485; Sat, 09 Mar 2024 12:24:51 -0800 (PST) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id kv13-20020a17090328cd00b001dc91b4081dsm1689004plb.271.2024.03.09.12.24.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 09 Mar 2024 12:24:51 -0800 (PST) From: Kees Cook To: Jeremy Linton Cc: Kees Cook , Arnd Bergmann , "Gustavo A. R. Silva" , linux-hardening@vger.kernel.org, Elena Reshetova , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH] randomize_kstack: Improve entropy diffusion Date: Sat, 9 Mar 2024 12:24:48 -0800 Message-Id: <20240309202445.work.165-kees@kernel.org> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1133; i=keescook@chromium.org; h=from:subject:message-id; bh=K9RoT73X71QnB+uU8sWtSEx1Mtsrf1E5zhfyiv3p1ZE=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBl7MWQSFajPauij2zI2NqidKesJzjt4bPzfLCaH yknBCinsCGJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZezFkAAKCRCJcvTf3G3A Jmw7D/9F0pyXIKqu9kZmrjuYv8/kfrd8EBz4K3EsSJ877q3bmqlQxMfJwm/KOL/Wt6HVE0a/P8a dHAS5wUM14FBGvPkoEmUPu2kuxeegqRC2FCKCuvx2JiiXFVoQ/YF3RHw6XNosQUi465oFMZHf7i wArtIwAloVlVK5fvYEvDoYP/fmZ+cgUxuraqrTDQZRQq637paFp+HGthtvdQd81bV4mrwDoKrpm FFPbq5uvAKued3ymyZ4XFRYy7ryBz8reIgIyxACSnBX8PG5ZY/JX9eFX5Dgglyd+epZ+wkeOV3Q y8mk8G+7vK/3CInx+EXsjU2biIIRKgHSYaCa2G79XRL6YiJH5y4HgONJVCZ5EgG2F91yhGuCYsi zyNVm77/4EQ1EFjhP0qSritGVorn3HavQlWvSnk//b2z+VcZVQ5168aImJCyhI5IbTdKyjjxfGC WnPMAnkqPIkPvhM2o9C8I7fP5FLY09G/hcZNW7pz+3G7tbOd5eEe4NqaUKqchu4KT+/3gnuWYE6 pmEruvww9YJn5ZcMteecUkWWHrUDMOwLu/lROpmnh00fUcs0zfg58ynqC1v0UPacrXxZH31MYzW YnRnu++vJJEhejWU18Lxkc8JugyphNk95dSlnqhKjCnXnvU5qgxbV4ieXmq4OWM6J3uhbLHAZEr aXbZzcE j2hbFSUQ== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The kstack_offset variable was really only ever using the low bits for kernel stack offset entropy. Add a ror32() to increase bit diffusion. Suggested-by: Arnd Bergmann Fixes: 39218ff4c625 ("stack: Optionally randomize kernel stack offset each = syscall") Signed-off-by: Kees Cook --- Cc: Jeremy Linton Cc: "Gustavo A. R. Silva" Cc: linux-hardening@vger.kernel.org --- include/linux/randomize_kstack.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kst= ack.h index 5d868505a94e..6d92b68efbf6 100644 --- a/include/linux/randomize_kstack.h +++ b/include/linux/randomize_kstack.h @@ -80,7 +80,7 @@ DECLARE_PER_CPU(u32, kstack_offset); if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ &randomize_kstack_offset)) { \ u32 offset =3D raw_cpu_read(kstack_offset); \ - offset ^=3D (rand); \ + offset =3D ror32(offset, 5) ^ (rand); \ raw_cpu_write(kstack_offset, offset); \ } \ } while (0) --=20 2.34.1