Received-SPF: pass (google.com: domain of linux-kernel+bounces-126929-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Message-ID: <133312c4-6ddb-4752-a7fa-3e7e526e9335@amd.com>
Date: Mon, 1 Apr 2024 12:57:03 -0500
User-Agent: Mozilla Thunderbird
Reply-To: babu.moger@amd.com
Subject: Re: [PATCH] x86/resctrl: Fix uninitialized memory read when last CPU
 of domain goes offline
To: Reinette Chatre <reinette.chatre@intel.com>, fenghua.yu@intel.com,
 bp@alien8.de, james.morse@arm.com, tony.luck@intel.com,
 peternewman@google.com, tglx@linutronix.de, mingo@redhat.com,
 dave.hansen@linux.intel.com, x86@kernel.org
Cc: hpa@zytor.com, james.greenhalgh@arm.com, linux-kernel@vger.kernel.org
References: <979cfd9522021aa6001f8995cd36fb56e1c9cd39.1711659804.git.reinette.chatre@intel.com>
Content-Language: en-US
From: "Moger, Babu" <babu.moger@amd.com>
In-Reply-To: <979cfd9522021aa6001f8995cd36fb56e1c9cd39.1711659804.git.reinette.chatre@intel.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0:
	=?utf-8?B?U1FtY3kvRlJLNlRvR1dnNU5GSUdFUm42R3NoU0NRZFhyWWdjaXR5WGp1UFdt?=
 =?utf-8?B?Nk1iMFFrOUN4UWpULzhvWTJPY21hUjMwVHFxUnYwVzU4RGNlaFB4MG04bkVw?=
 =?utf-8?B?UTNVWnNYdU9nT0tBREpNUmRCUU5RYTRweGRWdjhhUzlwYU5mYVNuUE1SaStR?=
 =?utf-8?B?Y3VXbGNjZWZxbXcyYUxJMG5QdnNiUFBSdjJJM1RCMkVOZ1R4VzFiM0hSMXlE?=
 =?utf-8?B?TFBJTWYrNUl0ZFhiVHh1eklEUE43djV6VlQ3NitRRDFYR04zZWl2VEd0NHo0?=
 =?utf-8?B?SWtLcERPNVZGVThCYkx0ZHZTYmVsa3d4VzJWOVVhVDNHVDNQMTZZeHlZZ3hr?=
 =?utf-8?B?bEpNclZzbysxdlk4NHk4RElub3ZNSHpjMkFUSWt3MTIyY1F4NDNtTXRHeEFN?=
 =?utf-8?B?ZEFndWNneFFNUXZVNDdUUEhwTEJzOU9Dd1h5bm1Nelg5Yk5oUXAxVk9ud0E2?=
 =?utf-8?B?QjA3UjdZNXpDTllUc0twL3o3Qjd6VjlBUy9YQkdaaHBJSFNjVldGOEhROWh6?=
 =?utf-8?B?akc2alNpTnNJRmxRQWg2QkhtZmFUSUhOQjZoMlJFRXNlUDhhNDRIQUlpK2Zr?=
 =?utf-8?B?eE0vTG5tUXkyWGd3ZW9wL2syZEJzQnN0U25aeDFlWVdHNVVoMWZ1NDFJSUV0?=
 =?utf-8?B?VU9RaUlHV2FCUk1ydnYzSmF5SWY1L295UndXS2EraHlWNThaRHpzMGlLSzBF?=
 =?utf-8?B?QUFHWVJBQXg5V3RNdi90Vld4eTJqeWd6V2lqbFRHZ2ZtcCtLYU1ad0xNaklO?=
 =?utf-8?B?Zk5rNzh5SDhPb0FBVjNZNVBpczZXM05jTjVMemVrQnlIYS9PbzdJZlc4WWU3?=
 =?utf-8?B?dmNWTGsvU0lObGZMcjBTdFVQc2pMNTlBaWNrT0lFdzluR0NoamQ3WWdESzBm?=
 =?utf-8?B?M1pOU1I0eE1ha2cxc3llZTI5d29OV2dGZ2ZDRWZZVE1GUnR3eHN5dlh1RHla?=
 =?utf-8?B?cS9QNWY1UlU5YnlteVUxT3ZvS1d2dEZ6dUZhSW04UFcxOVVpZ0lMMUNoYjlt?=
 =?utf-8?B?NmNpZmJETDN3QmtrYktyd2FvRGJOVjZSc3FvVmNNWk9CU1VYelI4SHVLWEhW?=
 =?utf-8?B?R0JGU2hqU0p1QTk3S1RiZXlDZzhBSSt5REVEVkxzc2hHcDNyQXNYNWNLd1lj?=
 =?utf-8?B?OUNIUFF1eVpqcnJPam4xMHJOSzhRTmIxdCtvcmxmSW1LT0dFbU51aS9MeHpK?=
 =?utf-8?B?SmNWTTNCMzRzbzhaZ2J2MGhsbTdsUVk5NjdScGhLWUUxZEh1UTc2MDlTNmdS?=
 =?utf-8?B?TFZXM2IzdFRNUmJNd0Z1c1lhazRqOW5ubGNoWGFIYVU2K0JsRUNuZGVWemU4?=
 =?utf-8?B?MUNVUndIQXFBZEc2b081Z3lKZXZGZUdQYTdwT0owWFZxR0Qvb2N6Vk54OUNU?=
 =?utf-8?B?N3dkbHpMWXBLM3M4UjNDaVYvQ1VINzNCNHFyWGVuSmN3NGVwVmVHUG8yTmoy?=
 =?utf-8?B?aEQ3aHNEbWxCTVpYNTl2QWVSSUQxSzh5VmRTdGprSWZJRlBzUnZMMFRvYTRn?=
 =?utf-8?B?YWJzVm9rbFV1bU41MmQ2ZTJ0cElhWWxlVThMbS84V0ZraXUwbGxWdHVzRHRx?=
 =?utf-8?B?cEUvdC9XbWMvZjFsWTROem9zek5KaEdLd3BpNnJPcXh1ZlI1Wmt3ZGF4cm1j?=
 =?utf-8?B?azJnd3MxVzlrT2NHQzF5eXVRb1ErWUJrNTJsMWxlWjJXQUVWZUlpaTV3MmI4?=
 =?utf-8?B?eVRxdkRjNlVSVlM2ZkZkY1AwTkRvc3NNaG5nYXdLRXlrb1c5L2lPRzRUYnhr?=
 =?utf-8?B?VzFwb0pjRzREL0dqeVVXcCtBZlc0aktsN1AvQzhnenNhSm83cCtpbUFtbXlj?=
 =?utf-8?B?NkR3dWNGa0o3ay9jUVcvbzhVdHVleU1YdENMNnppajZkVzBBdzBqNTg2bENR?=
 =?utf-8?B?YUNYdWpaT1U0L2ZOcjFoeENYZDZhVnYvSjVvK2huM1lRc242YWtvS3JKaTlo?=
 =?utf-8?B?bmNXcHI0blJGdnpVMGIwMnd6ck1YRitrTnp2a3F1cjk0UkN2L3BMY3NZSFRh?=
 =?utf-8?B?RXBuWWtKVEExczlyVlBsakZzbzdaSVRMWEtqU1RtSFRoalMxUk10RWk4Rm1K?=
 =?utf-8?B?YXRmYXN3c3pyS05hZ0dzSnQ3cldISUZMUVNRWVlqZzN5YnhvN1c1dURCRktz?=
 =?utf-8?Q?QQcI=3D?=
X-OriginatorOrg: amd.com
X-MS-Exchange-CrossTenant-Network-Message-Id: fb794cdb-2a37-4eff-85d7-08dc527524a8
X-MS-Exchange-CrossTenant-AuthSource: MW3PR12MB4553.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Apr 2024 17:57:06.0709
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: BruQ1HANRuAVsnAvUA9b2EG5KMdqhQSup2B0neStOyL1qmQN9Z2AzV1EmHuYmHMH
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR12MB6377

Hi Reinette,

On 3/28/24 16:12, Reinette Chatre wrote:
> Tony encountered the OOPS below when the last CPU of a domain goes
> offline while running a kernel built with CONFIG_NO_HZ_FULL:
> 
>     BUG: kernel NULL pointer dereference, address: 0000000000000000
>     #PF: supervisor read access in kernel mode
>     #PF: error_code(0x0000) - not-present page
>     PGD 0
>     Oops: 0000 [#1] PREEMPT SMP NOPTI
>     ...
>     RIP: 0010:__find_nth_andnot_bit+0x66/0x110
>     ...
>     Call Trace:
>      <TASK>
>      ? __die+0x1f/0x60
>      ? page_fault_oops+0x176/0x5a0
>      ? exc_page_fault+0x7f/0x260
>      ? asm_exc_page_fault+0x22/0x30
>      ? __pfx_resctrl_arch_offline_cpu+0x10/0x10
>      ? __find_nth_andnot_bit+0x66/0x110
>      ? __cancel_work+0x7d/0xc0
>      cpumask_any_housekeeping+0x55/0x110
>      mbm_setup_overflow_handler+0x40/0x70
>      resctrl_offline_cpu+0x101/0x110
>      resctrl_arch_offline_cpu+0x19/0x260
>      cpuhp_invoke_callback+0x156/0x6b0
>      ? cpuhp_thread_fun+0x5f/0x250
>      cpuhp_thread_fun+0x1ca/0x250
>      ? __pfx_smpboot_thread_fn+0x10/0x10
>      smpboot_thread_fn+0x184/0x220
>      kthread+0xe0/0x110
>      ? __pfx_kthread+0x10/0x10
>      ret_from_fork+0x2d/0x50
>      ? __pfx_kthread+0x10/0x10
>      ret_from_fork_asm+0x1a/0x30
>      </TASK>
> 
> The NULL pointer dereference is encountered while searching for another
> online CPU in the domain (of which there are none) that can be used to
> run the MBM overflow handler.
> 
> Because the kernel is configured with CONFIG_NO_HZ_FULL the search for
> another CPU (in its effort to prefer those CPUs that aren't marked
> nohz_full) consults the mask representing the nohz_full CPUs,
> tick_nohz_full_mask. On a kernel with CONFIG_CPUMASK_OFFSTACK=y
> tick_nohz_full_mask is not allocated unless the kernel is booted with
> the "nohz_full=" parameter and because of that any access to
> tick_nohz_full_mask needs to be guarded with tick_nohz_full_enabled().
> 
> Add a tick_nohz_full_enabled() check to ensure that tick_nohz_full_mask
> has been initialized and can thus be accessed safely.
> 
> Fixes: a4846aaf3945 ("x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow")
> Reported-by: Tony Luck <tony.luck@intel.com>
> Closes: https://lore.kernel.org/lkml/ZgIFT5gZgIQ9A9G7@agluck-desk3/
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
>  arch/x86/kernel/cpu/resctrl/internal.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index c99f26ebe7a6..4f9ef35626a7 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -85,6 +85,10 @@ cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
>  	if (cpu < nr_cpu_ids && !tick_nohz_full_cpu(cpu))
>  		return cpu;
>  
> +	/* Only continue if tick_nohz_full_mask has been initialized. */
> +	if (!tick_nohz_full_enabled())
> +		return cpu;
> +

I am curious why this below check didn't fail?

if (cpu < nr_cpu_ids && !tick_nohz_full_cpu(cpu))
  		return cpu;

The tick_nohz_full_cpu() already checks tick_nohz_full_enabled().

It should returned 'false' and  returned cpu already.

Did i miss something?

-- 
Thanks
Babu Moger