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

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 <redacted>
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))

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