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

Matthew Garrett
2019-06-22T00:05:08Z

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))
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