diff mbox series

[v6,24/24] bpf: Fail bpf_probe_write_user() while mm is switched

Message ID 20190426232303.28381-25-nadav.amit@gmail.com (mailing list archive)
State New, archived
Headers show
Series x86: text_poke() fixes and executable lockdowns | expand

Commit Message

Nadav Amit April 26, 2019, 11:23 p.m. UTC 
From: Nadav Amit <namit@vmware.com>

When using a temporary mm, bpf_probe_write_user() should not be able to
write to user memory, since user memory addresses may be used to map
kernel memory.  Detect these cases and fail bpf_probe_write_user() in
such cases.

Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Reported-by: Jann Horn <jannh@google.com>
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 kernel/trace/bpf_trace.c | 8 ++++++++
 1 file changed, 8 insertions(+)
diff mbox series

Patch

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d64c00afceb5..94b0e37d90ef 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -14,6 +14,8 @@ 
 #include <linux/syscalls.h>
 #include <linux/error-injection.h>
 
+#include <asm/tlb.h>
+
 #include "trace_probe.h"
 #include "trace.h"
 
@@ -163,6 +165,10 @@  BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src,
 	 * access_ok() should prevent writing to non-user memory, but in
 	 * some situations (nommu, temporary switch, etc) access_ok() does
 	 * not provide enough validation, hence the check on KERNEL_DS.
+	 *
+	 * nmi_uaccess_okay() ensures the probe is not run in an interim
+	 * state, when the task or mm are switched. This is specifically
+	 * required to prevent the use of temporary mm.
 	 */
 
 	if (unlikely(in_interrupt() ||
@@ -170,6 +176,8 @@  BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src,
 		return -EPERM;
 	if (unlikely(uaccess_kernel()))
 		return -EPERM;
+	if (unlikely(!nmi_uaccess_okay()))
+		return -EPERM;
 	if (!access_ok(unsafe_ptr, size))
 		return -EPERM;