[PATCH V35 24/29] 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>
Reviewed-by: Kees Cook <keesc...@chromium.org>
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         | 7 +++++++
 security/lockdown/lockdown.c | 1 +
 3 files changed, 9 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 8dd1741a52cd..8ef366de70b0 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -119,6 +119,7 @@ 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 785d708f8553..738d6f1cf5ec 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10806,6 +10806,13 @@ SYSCALL_DEFINE5(perf_event_open,
            perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
                return -EACCES;
 
+       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;
+
+       err = 0;
+
        /*
         * In cgroup mode, the pid argument is used to pass the fd
         * opened to the cgroup directory in cgroupfs. The cpu argument
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index d14b89784412..e43c9d001e49 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",
 };
 
-- 
2.22.0.510.g264f2c817a-goog