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

[Matthew Garrett]

From: David Howells <dhowells@xxxxxxxxxx>

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

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 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