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 D994129CA for ; Wed, 22 May 2024 06:20:31 +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=1716358831; cv=none; b=nGYpwH15KCZXzwepHD7yIGnGzNrJ5wz/VoWgS/gj3hdhceioad6DdKI5Hcl0y1HyEkdxCmSJbwtxlbpzNKlaT9Rhc3dDf/uZO/GswWwOLpow2r422L7tlSjsvUFZOhOhMU87aUiFhtdLtsaZ2dUFhxLnsDLYhqSbhE2Gs0Hx4CE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716358831; c=relaxed/simple; bh=20ELcvi6tJD9wCKOkxbQ+LrNmTICVNTdyqG+yBEzaJk=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=EHtjKni7sfANT6opurCdyqKLC2zb/jUL4Ga/jUotgPvHG63wFEOk6VmziK7vU6ZsRLdp21z+yXDMqTfPPGCgJ2ipm52m8gzfv1MGwnlehPGxC2Aykxyp+tbukCYK/vr7Q/fDQEB+8Z9ul3G0iGOEmQXsK5Al0vCyMQGKezrCHN8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=2J+Ai7U6; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="2J+Ai7U6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 58746C2BD11; Wed, 22 May 2024 06:20:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1716358831; bh=20ELcvi6tJD9wCKOkxbQ+LrNmTICVNTdyqG+yBEzaJk=; h=From:To:Cc:Subject:Date:Reply-to:From; b=2J+Ai7U6M7rRae/ZEBbN9uLmyyjMnOLK/8Fe3Iex9w6FWfJS+iClmDK/m46+W6ss/ CA4DfGNnsEwIkuxi2HYtSaGeIpvChs2n1y3ugAbXMXblpli1xSXZD1X2vA6glXmElx +/Yzn3WPoOU1dFsDX8qigAtM8xOVJwwTb6apLBi8= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2021-47454: powerpc/smp: do not decrement idle task preempt count in CPU offline Date: Wed, 22 May 2024 08:19:57 +0200 Message-ID: <2024052243-CVE-2021-47454-e852@gregkh> X-Mailer: git-send-email 2.45.1 Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Reply-to: , X-Developer-Signature: v=1; a=openpgp-sha256; l=3109; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=20ELcvi6tJD9wCKOkxbQ+LrNmTICVNTdyqG+yBEzaJk=; b=owGbwMvMwCRo6H6F97bub03G02pJDGm+ffW2J8LeWazbxnYvN7yvNrZdT0FUOpD1+JVlrydce PDu+r7tHbEsDIJMDLJiiixftvEc3V9xSNHL0PY0zBxWJpAhDFycAjARDjmGBRMv3pin39S8cNLm IptD3qHzZmdt7GFYsFtfvyXq1SKXnSXt8Vf7n9r3qZ/5DgA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit Description =========== In the Linux kernel, the following vulnerability has been resolved: powerpc/smp: do not decrement idle task preempt count in CPU offline With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we get: BUG: scheduling while atomic: swapper/1/0/0x00000000 no locks held by swapper/1/0. CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100 Call Trace: dump_stack_lvl+0xac/0x108 __schedule_bug+0xac/0xe0 __schedule+0xcf8/0x10d0 schedule_idle+0x3c/0x70 do_idle+0x2d8/0x4a0 cpu_startup_entry+0x38/0x40 start_secondary+0x2ec/0x3a0 start_secondary_prolog+0x10/0x14 This is because powerpc's arch_cpu_idle_dead() decrements the idle task's preempt count, for reasons explained in commit a7c2bb8279d2 ("powerpc: Re-enable preemption before cpu_die()"), specifically "start_secondary() expects a preempt_count() of 0." However, since commit 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug") and commit f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled"), that justification no longer holds. The idle task isn't supposed to re-enable preemption, so remove the vestigial preempt_enable() from the CPU offline path. Tested with pseries and powernv in qemu, and pseries on PowerVM. The Linux kernel CVE team has assigned CVE-2021-47454 to this issue. Affected and fixed versions =========================== Issue introduced in 5.10.50 with commit bdf4d33e8342 and fixed in 5.10.76 with commit 53770a411559 Issue introduced in 5.14 with commit 2c669ef6979c and fixed in 5.14.15 with commit 3ea0b497a7a2 Issue introduced in 5.14 with commit 2c669ef6979c and fixed in 5.15 with commit 787252a10d94 Issue introduced in 5.12.17 with commit 2b6148ef2bd6 Issue introduced in 5.13.2 with commit 20a015e948b8 Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2021-47454 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: arch/powerpc/kernel/smp.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/53770a411559cf7bc0906d1df319cc533d2f4f58 https://git.kernel.org/stable/c/3ea0b497a7a2fff6a4b7090310c9f52c91975934 https://git.kernel.org/stable/c/787252a10d9422f3058df9a4821f389e5326c440