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Date: Mon, 22 Apr 2019 11:58:05 -0700
From: Rick Edgecombe <rick.p.edgecombe@...el.com>
To: Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>,
	Ingo Molnar <mingo@...hat.com>
Cc: linux-kernel@...r.kernel.org,
	x86@...nel.org,
	hpa@...or.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux_dti@...oud.com,
	linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	akpm@...ux-foundation.org,
	kernel-hardening@...ts.openwall.com,
	linux-mm@...ck.org,
	will.deacon@....com,
	ard.biesheuvel@...aro.org,
	kristen@...ux.intel.com,
	deneen.t.dock@...el.com,
	Nadav Amit <namit@...are.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...nel.org>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: [PATCH v4 23/23] bpf: Fail bpf_probe_write_user() while mm is switched

From: Nadav Amit <namit@...are.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@...earbox.net>
Cc: Alexei Starovoitov <ast@...nel.org>
Reported-by: Jann Horn <jannh@...gle.com>
Suggested-by: Jann Horn <jannh@...gle.com>
Signed-off-by: Nadav Amit <namit@...are.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
---
 kernel/trace/bpf_trace.c | 8 ++++++++
 1 file changed, 8 insertions(+)

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;
 
-- 
2.17.1

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