Re: [PATCH v6 01/10] capabilities: introduce CAP_PERFMON to kernel and user space

[Alexey Budankov]

On 06.02.2020 21:23, Stephen Smalley wrote:
> On 2/5/20 12:30 PM, Alexey Budankov wrote:
>>
>> Introduce CAP_PERFMON capability designed to secure system performance
>> monitoring and observability operations so that CAP_PERFMON would assist
>> CAP_SYS_ADMIN capability in its governing role for performance monitoring
>> and observability subsystems.
>>
>> CAP_PERFMON hardens system security and integrity during performance
>> monitoring and observability operations by decreasing attack surface that
>> is available to a CAP_SYS_ADMIN privileged process [2]. Providing the access
>> to system performance monitoring and observability operations under CAP_PERFMON
>> capability singly, without the rest of CAP_SYS_ADMIN credentials, excludes
>> chances to misuse the credentials and makes the operation more secure.
>> Thus, CAP_PERFMON implements the principal of least privilege for performance
>> monitoring and observability operations (POSIX IEEE 1003.1e: 2.2.2.39 principle
>> of least privilege: A security design principle that states that a process
>> or program be granted only those privileges (e.g., capabilities) necessary
>> to accomplish its legitimate function, and only for the time that such
>> privileges are actually required)
>>
>> CAP_PERFMON meets the demand to secure system performance monitoring and
>> observability operations for adoption in security sensitive, restricted,
>> multiuser production environments (e.g. HPC clusters, cloud and virtual compute
>> environments), where root or CAP_SYS_ADMIN credentials are not available to
>> mass users of a system, and securely unblocks accessibility of system performance monitoring and observability operations beyond root and CAP_SYS_ADMIN use cases.
>>
>> CAP_PERFMON takes over CAP_SYS_ADMIN credentials related to system performance
>> monitoring and observability operations and balances amount of CAP_SYS_ADMIN
>> credentials following the recommendations in the capabilities man page [1]
>> for CAP_SYS_ADMIN: "Note: this capability is overloaded; see Notes to kernel
>> developers, below." For backward compatibility reasons access to system
>> performance monitoring and observability subsystems of the kernel remains
>> open for CAP_SYS_ADMIN privileged processes but CAP_SYS_ADMIN capability
>> usage for secure system performance monitoring and observability operations
>> is discouraged with respect to the designed CAP_PERFMON capability.
>>
>> Although the software running under CAP_PERFMON can not ensure avoidance
>> of related hardware issues, the software can still mitigate these issues
>> following the official hardware issues mitigation procedure [2]. The bugs
>> in the software itself can be fixed following the standard kernel development
>> process [3] to maintain and harden security of system performance monitoring
>> and observability operations.
>>
>> [1] http://man7.org/linux/man-pages/man7/capabilities.7.html
>> [2] https://www.kernel.org/doc/html/latest/process/embargoed-hardware-issues.html
>> [3] https://www.kernel.org/doc/html/latest/admin-guide/security-bugs.html
>>
>> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
> 
> This will require a small update to the selinux-testsuite to correctly reflect the new capability requirements, but that's easy enough.

Is the suite a part of the kernel sources or something else?

~Alexey

> 
> Acked-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
> 
>> ---
>> Â include/linux/capability.hÂÂÂÂÂÂÂÂÂ | 4 ++++
>> Â include/uapi/linux/capability.hÂÂÂÂ | 8 +++++++-
>> Â security/selinux/include/classmap.h | 4 ++--
>> Â 3 files changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/capability.h b/include/linux/capability.h
>> index ecce0f43c73a..027d7e4a853b 100644
>> --- a/include/linux/capability.h
>> +++ b/include/linux/capability.h
>> @@ -251,6 +251,10 @@ extern bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct
>> Â extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
>> Â extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
>> Â extern bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns);
>> +static inline bool perfmon_capable(void)
>> +{
>> +ÂÂÂ return capable(CAP_PERFMON) || capable(CAP_SYS_ADMIN);
>> +}
>> Â Â /* audit system wants to get cap info from files as well */
>> Â extern int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps);
>> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
>> index 240fdb9a60f6..8b416e5f3afa 100644
>> --- a/include/uapi/linux/capability.h
>> +++ b/include/uapi/linux/capability.h
>> @@ -366,8 +366,14 @@ struct vfs_ns_cap_data {
>> Â Â #define CAP_AUDIT_READÂÂÂÂÂÂÂ 37
>> Â +/*
>> + * Allow system performance and observability privileged operations
>> + * using perf_events, i915_perf and other kernel subsystems
>> + */
>> +
>> +#define CAP_PERFMONÂÂÂÂÂÂÂ 38
>> Â -#define CAP_LAST_CAPÂÂÂÂÂÂÂÂ CAP_AUDIT_READ
>> +#define CAP_LAST_CAPÂÂÂÂÂÂÂÂ CAP_PERFMON
>> Â Â #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
>> Â diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
>> index 7db24855e12d..c599b0c2b0e7 100644
>> --- a/security/selinux/include/classmap.h
>> +++ b/security/selinux/include/classmap.h
>> @@ -27,9 +27,9 @@
>> ÂÂÂÂÂÂÂÂÂ "audit_control", "setfcap"
>> Â Â #define COMMON_CAP2_PERMSÂ "mac_override", "mac_admin", "syslog", \
>> -ÂÂÂÂÂÂÂ "wake_alarm", "block_suspend", "audit_read"
>> +ÂÂÂÂÂÂÂ "wake_alarm", "block_suspend", "audit_read", "perfmon"
>> Â -#if CAP_LAST_CAP > CAP_AUDIT_READ
>> +#if CAP_LAST_CAP > CAP_PERFMON
>> Â #error New capability defined, please update COMMON_CAP2_PERMS.
>> Â #endif
>> Â
>