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Message-ID: <CABXk95AO_nxb+xFqJuU8r3mzx+oVJrRcJcYBF3xM=c7krCapwQ@mail.gmail.com>
Date: Sat, 4 Jun 2016 13:56:54 -0700
From: Jeffrey Vander Stoep <jeffv@...gle.com>
To: kernel-hardening@...ts.openwall.com
Cc: "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] security,perf: Allow further
restriction of perf_event_open
Acked-by: Jeff Vander Stoep <jeffv@...gle.com>
In addition to Debian, this patch has been merged into AOSP and is a
requirement for Android:
https://android-review.googlesource.com/#/q/topic:CONFIG_SECURITY_PERF_EVENTS_RESTRICT
On Wed, Apr 13, 2016 at 9:12 AM, Kees Cook <keescook@...omium.org> wrote:
> On Mon, Jan 11, 2016 at 7:23 AM, Ben Hutchings <ben@...adent.org.uk> wrote:
>> When kernel.perf_event_open is set to 3 (or greater), disallow all
>> access to performance events by users without CAP_SYS_ADMIN.
>> Add a Kconfig symbol CONFIG_SECURITY_PERF_EVENTS_RESTRICT that
>> makes this value the default.
>>
>> This is based on a similar feature in grsecurity
>> (CONFIG_GRKERNSEC_PERF_HARDEN). This version doesn't include making
>> the variable read-only. It also allows enabling further restriction
>> at run-time regardless of whether the default is changed.
>>
>> Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
>
> Whoops, I entirely missed this email! Just found it now.
>
> Ben, can you resend this with Perf maintainers in CC? This seems
> sensible enough to me.
>
> -Kees
>
>> ---
>> I made a similar change to Debian's kernel packages in August,
>> including the more restrictive default, and no-one has complained yet.
>>
>> Ben.
>>
>> Documentation/sysctl/kernel.txt | 4 +++-
>> include/linux/perf_event.h | 5 +++++
>> kernel/events/core.c | 8 ++++++++
>> security/Kconfig | 9 +++++++++
>> 4 files changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
>> index 88a2c8e..76e2ca8 100644
>> --- a/Documentation/sysctl/kernel.txt
>> +++ b/Documentation/sysctl/kernel.txt
>> @@ -629,12 +629,14 @@ allowed to execute.
>> perf_event_paranoid:
>>
>> Controls use of the performance events system by unprivileged
>> -users (without CAP_SYS_ADMIN). The default value is 1.
>> +users (without CAP_SYS_ADMIN). The default value is 3 if
>> +CONFIG_SECURITY_PERF_EVENTS_RESTRICT is set, or 1 otherwise.
>>
>> -1: Allow use of (almost) all events by all users
>> >=0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
>> >=1: Disallow CPU event access by users without CAP_SYS_ADMIN
>> >=2: Disallow kernel profiling by users without CAP_SYS_ADMIN
>> +>=3: Disallow all event access by users without CAP_SYS_ADMIN
>>
>> ==============================================================
>>
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index f9828a4..aa72940 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -989,6 +989,11 @@ extern int perf_cpu_time_max_percent_handler(struct ctl_table *table, int write,
>> loff_t *ppos);
>>
>>
>> +static inline bool perf_paranoid_any(void)
>> +{
>> + return sysctl_perf_event_paranoid > 2;
>> +}
>> +
>> static inline bool perf_paranoid_tracepoint_raw(void)
>> {
>> return sysctl_perf_event_paranoid > -1;
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index cfc227c..85bc810 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -175,8 +175,13 @@ static struct srcu_struct pmus_srcu;
>> * 0 - disallow raw tracepoint access for unpriv
>> * 1 - disallow cpu events for unpriv
>> * 2 - disallow kernel profiling for unpriv
>> + * 3 - disallow all unpriv perf event use
>> */
>> +#ifdef CONFIG_SECURITY_PERF_EVENTS_RESTRICT
>> +int sysctl_perf_event_paranoid __read_mostly = 3;
>> +#else
>> int sysctl_perf_event_paranoid __read_mostly = 1;
>> +#endif
>>
>> /* Minimum for 512 kiB + 1 user control page */
>> int sysctl_perf_event_mlock __read_mostly = 512 + (PAGE_SIZE / 1024); /* 'free' kiB per user */
>> @@ -8265,6 +8270,9 @@ SYSCALL_DEFINE5(perf_event_open,
>> if (flags & ~PERF_FLAG_ALL)
>> return -EINVAL;
>>
>> + if (perf_paranoid_any() && !capable(CAP_SYS_ADMIN))
>> + return -EACCES;
>> +
>> err = perf_copy_attr(attr_uptr, &attr);
>> if (err)
>> return err;
>> diff --git a/security/Kconfig b/security/Kconfig
>> index e452378..30a2603 100644
>> --- a/security/Kconfig
>> +++ b/security/Kconfig
>> @@ -18,6 +18,15 @@ config SECURITY_DMESG_RESTRICT
>>
>> If you are unsure how to answer this question, answer N.
>>
>> +config SECURITY_PERF_EVENTS_RESTRICT
>> + bool "Restrict unprivileged use of performance events"
>> + depends on PERF_EVENTS
>> + help
>> + If you say Y here, the kernel.perf_event_paranoid sysctl
>> + will be set to 3 by default, and no unprivileged use of the
>> + perf_event_open syscall will be permitted unless it is
>> + changed.
>> +
>> config SECURITY
>> bool "Enable different security models"
>> depends on SYSFS
>
>
>
> --
> Kees Cook
> Chrome OS & Brillo Security
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