[PATCH V33 25/30] Lock down perf when in confidentiality mode

[Matthew Garrett]

From: David Howells <dhowe...@redhat.com>

Disallow the use of certain perf facilities that might allow userspace to
access kernel data.

Signed-off-by: David Howells <dhowe...@redhat.com>
Signed-off-by: Matthew Garrett <mj...@google.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
---
 include/linux/security.h     | 1 +
 kernel/events/core.c         | 5 +++++
 security/lockdown/lockdown.c | 1 +
 3 files changed, 7 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 8bf426cdd151..36a9daa13bb0 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -98,6 +98,7 @@ enum lockdown_reason {
        LOCKDOWN_KCORE,
        LOCKDOWN_KPROBES,
        LOCKDOWN_BPF,
+       LOCKDOWN_PERF,
        LOCKDOWN_CONFIDENTIALITY_MAX,
 };
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 72d06e302e99..ac1045caa44d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10731,6 +10731,11 @@ SYSCALL_DEFINE5(perf_event_open,
                        return -EINVAL;
        }
 
+       if ((attr.sample_type & PERF_SAMPLE_REGS_INTR) &&
+           security_is_locked_down(LOCKDOWN_PERF))
+               /* REGS_INTR can leak data, lockdown must prevent this */
+               return -EPERM;
+
        /* Only privileged users can get physical addresses */
        if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
            perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 0a3bbf1ba01d..14edc475d75c 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] = "use of bpf",
+       [LOCKDOWN_PERF] = "unsafe use of perf",
        [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
 
-- 
2.22.0.410.gd8fdbe21b5-goog