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Message-ID: <20190426001143.4983-24-namit@vmware.com>
Date: Thu, 25 Apr 2019 17:11:43 -0700
From: Nadav Amit <namit@...are.com>
To: Peter Zijlstra <peterz@...radead.org>, 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>, <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>, Rick Edgecombe
<rick.p.edgecombe@...el.com>, Nadav Amit <namit@...are.com>, Daniel Borkmann
<daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>
Subject: [PATCH v5 23/23] bpf: Fail bpf_probe_write_user() while mm is switched
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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