|
Jiri Slaby |
2e024a |
From: Dave Hansen <dave.hansen@linux.intel.com>
|
|
Jiri Slaby |
2e024a |
Date: Tue, 21 Feb 2023 12:30:15 -0800
|
|
Jiri Slaby |
2e024a |
Subject: [PATCH] uaccess: Add speculation barrier to copy_from_user()
|
|
Jiri Slaby |
2e024a |
References: bsc#1012628
|
|
Jiri Slaby |
2e024a |
Patch-mainline: 6.2.1
|
|
Jiri Slaby |
2e024a |
Git-commit: 74e19ef0ff8061ef55957c3abd71614ef0f42f47
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
commit 74e19ef0ff8061ef55957c3abd71614ef0f42f47 upstream.
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
The results of "access_ok()" can be mis-speculated. The result is that
|
|
Jiri Slaby |
2e024a |
you can end speculatively:
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
if (access_ok(from, size))
|
|
Jiri Slaby |
2e024a |
// Right here
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
even for bad from/size combinations. On first glance, it would be ideal
|
|
Jiri Slaby |
2e024a |
to just add a speculation barrier to "access_ok()" so that its results
|
|
Jiri Slaby |
2e024a |
can never be mis-speculated.
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
But there are lots of system calls just doing access_ok() via
|
|
Jiri Slaby |
2e024a |
"copy_to_user()" and friends (example: fstat() and friends). Those are
|
|
Jiri Slaby |
2e024a |
generally not problematic because they do not _consume_ data from
|
|
Jiri Slaby |
2e024a |
userspace other than the pointer. They are also very quick and common
|
|
Jiri Slaby |
2e024a |
system calls that should not be needlessly slowed down.
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
"copy_from_user()" on the other hand uses a user-controller pointer and
|
|
Jiri Slaby |
2e024a |
is frequently followed up with code that might affect caches. Take
|
|
Jiri Slaby |
2e024a |
something like this:
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
if (!copy_from_user(&kernelvar, uptr, size))
|
|
Jiri Slaby |
2e024a |
do_something_with(kernelvar);
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
If userspace passes in an evil 'uptr' that *actually* points to a kernel
|
|
Jiri Slaby |
2e024a |
addresses, and then do_something_with() has cache (or other)
|
|
Jiri Slaby |
2e024a |
side-effects, it could allow userspace to infer kernel data values.
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
Add a barrier to the common copy_from_user() code to prevent
|
|
Jiri Slaby |
2e024a |
mis-speculated values which happen after the copy.
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
Also add a stub for architectures that do not define barrier_nospec().
|
|
Jiri Slaby |
2e024a |
This makes the macro usable in generic code.
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
Since the barrier is now usable in generic code, the x86 #ifdef in the
|
|
Jiri Slaby |
2e024a |
BPF code can also go away.
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
Reported-by: Jordy Zomer <jordyzomer@google.com>
|
|
Jiri Slaby |
2e024a |
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
|
|
Jiri Slaby |
2e024a |
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
|
|
Jiri Slaby |
2e024a |
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
|
|
Jiri Slaby |
2e024a |
Acked-by: Daniel Borkmann <daniel@iogearbox.net> # BPF bits
|
|
Jiri Slaby |
2e024a |
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Jiri Slaby |
2e024a |
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
|
|
Jiri Slaby |
2e024a |
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
|
|
Jiri Slaby |
2e024a |
---
|
|
Jiri Slaby |
2e024a |
include/linux/nospec.h | 4 ++++
|
|
Jiri Slaby |
2e024a |
kernel/bpf/core.c | 2 --
|
|
Jiri Slaby |
2e024a |
lib/usercopy.c | 7 +++++++
|
|
Jiri Slaby |
2e024a |
3 files changed, 11 insertions(+), 2 deletions(-)
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
diff --git a/include/linux/nospec.h b/include/linux/nospec.h
|
|
Jiri Slaby |
2e024a |
index c1e79f72..9f0af4f1 100644
|
|
Jiri Slaby |
2e024a |
--- a/include/linux/nospec.h
|
|
Jiri Slaby |
2e024a |
+++ b/include/linux/nospec.h
|
|
Jiri Slaby |
2e024a |
@@ -11,6 +11,10 @@
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
struct task_struct;
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
+#ifndef barrier_nospec
|
|
Jiri Slaby |
2e024a |
+# define barrier_nospec() do { } while (0)
|
|
Jiri Slaby |
2e024a |
+#endif
|
|
Jiri Slaby |
2e024a |
+
|
|
Jiri Slaby |
2e024a |
/**
|
|
Jiri Slaby |
2e024a |
* array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
|
|
Jiri Slaby |
2e024a |
* @index: array element index
|
|
Jiri Slaby |
2e024a |
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
|
|
Jiri Slaby |
2e024a |
index ba3fff17..430c66d5 100644
|
|
Jiri Slaby |
2e024a |
--- a/kernel/bpf/core.c
|
|
Jiri Slaby |
2e024a |
+++ b/kernel/bpf/core.c
|
|
Jiri Slaby |
2e024a |
@@ -1910,9 +1910,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
|
|
Jiri Slaby |
2e024a |
* reuse preexisting logic from Spectre v1 mitigation that
|
|
Jiri Slaby |
2e024a |
* happens to produce the required code on x86 for v4 as well.
|
|
Jiri Slaby |
2e024a |
*/
|
|
Jiri Slaby |
2e024a |
-#ifdef CONFIG_X86
|
|
Jiri Slaby |
2e024a |
barrier_nospec();
|
|
Jiri Slaby |
2e024a |
-#endif
|
|
Jiri Slaby |
2e024a |
CONT;
|
|
Jiri Slaby |
2e024a |
#define LDST(SIZEOP, SIZE) \
|
|
Jiri Slaby |
2e024a |
STX_MEM_##SIZEOP: \
|
|
Jiri Slaby |
2e024a |
diff --git a/lib/usercopy.c b/lib/usercopy.c
|
|
Jiri Slaby |
2e024a |
index 1505a52f..d29fe29c 100644
|
|
Jiri Slaby |
2e024a |
--- a/lib/usercopy.c
|
|
Jiri Slaby |
2e024a |
+++ b/lib/usercopy.c
|
|
Jiri Slaby |
2e024a |
@@ -3,6 +3,7 @@
|
|
Jiri Slaby |
2e024a |
#include <linux/fault-inject-usercopy.h>
|
|
Jiri Slaby |
2e024a |
#include <linux/instrumented.h>
|
|
Jiri Slaby |
2e024a |
#include <linux/uaccess.h>
|
|
Jiri Slaby |
2e024a |
+#include <linux/nospec.h>
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
/* out-of-line parts */
|
|
Jiri Slaby |
2e024a |
|
|
Jiri Slaby |
2e024a |
@@ -12,6 +13,12 @@ unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n
|
|
Jiri Slaby |
2e024a |
unsigned long res = n;
|
|
Jiri Slaby |
2e024a |
might_fault();
|
|
Jiri Slaby |
2e024a |
if (!should_fail_usercopy() && likely(access_ok(from, n))) {
|
|
Jiri Slaby |
2e024a |
+ /*
|
|
Jiri Slaby |
2e024a |
+ * Ensure that bad access_ok() speculation will not
|
|
Jiri Slaby |
2e024a |
+ * lead to nasty side effects *after* the copy is
|
|
Jiri Slaby |
2e024a |
+ * finished:
|
|
Jiri Slaby |
2e024a |
+ */
|
|
Jiri Slaby |
2e024a |
+ barrier_nospec();
|
|
Jiri Slaby |
2e024a |
instrument_copy_from_user_before(to, from, n);
|
|
Jiri Slaby |
2e024a |
res = raw_copy_from_user(to, from, n);
|
|
Jiri Slaby |
2e024a |
instrument_copy_from_user_after(to, from, n, res);
|
|
Jiri Slaby |
2e024a |
--
|
|
Jiri Slaby |
2e024a |
2.35.3
|
|
Jiri Slaby |
2e024a |
|