Re: [PATCH V34 24/29] Lock down perf when in confidentiality mode

Kees Cook
2019-06-23T00:12:41Z

On Fri, Jun 21, 2019 at 05:03:53PM -0700, Matthew Garrett wrote:
> From: David Howells <dhowells@redhat.com>
>
> Disallow the use of certain perf facilities that might allow userspace to
> access kernel data.
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Signed-off-by: Matthew Garrett <mjg59@google.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> ---
> include/linux/security.h | 1 +
> kernel/events/core.c | 7 +++++++
> security/lockdown/lockdown.c | 1 +
> 3 files changed, 9 insertions(+)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index de0d37b1fe79..53ea85889a48 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -98,6 +98,7 @@ enum lockdown_reason {
> LOCKDOWN_KCORE,
> LOCKDOWN_KPROBES,
> LOCKDOWN_BPF_READ,
> + LOCKDOWN_PERF,
> LOCKDOWN_CONFIDENTIALITY_MAX,
> };
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 72d06e302e99..77f36551756e 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -10731,6 +10731,13 @@ SYSCALL_DEFINE5(perf_event_open,
> return -EINVAL;
> }
>
> + err = security_locked_down(LOCKDOWN_PERF);
> + if (err && (attr.sample_type & PERF_SAMPLE_REGS_INTR))
> + /* REGS_INTR can leak data, lockdown must prevent this */
> + return err;
> + else
> + err = 0;
> +
> /* Only privileged users can get physical addresses */
> if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
> perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))

With moar capable() ordering fixed...

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index 2eea2cc13117..a7e75c614416 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -34,6 +34,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
> [LOCKDOWN_KCORE] = "/proc/kcore access",
> [LOCKDOWN_KPROBES] = "use of kprobes",
> [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
> + [LOCKDOWN_PERF] = "unsafe use of perf",
> [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
> };
>
> --
> 2.22.0.410.gd8fdbe21b5-goog
>

--
Kees Cook