[PATCH v3 2/4] uaccess: always export _copy_[from|to]_user with CONFIG_RUST

Alice Ryhl
2024-03-11T10:47:28Z

From: Arnd Bergmann <arnd@arndb.de>

Rust code needs to be able to access _copy_from_user and _copy_to_user
so that it can skip the check_copy_size check in cases where the length
is known at compile-time, mirroring the logic for when C code will skip
check_copy_size. To do this, we ensure that exported versions of these
methods are available when CONFIG_RUST is enabled.

Alice has verified that this patch passes the CONFIG_TEST_USER_COPY test
on x86 using the Android cuttlefish emulator.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
include/linux/uaccess.h | 38 ++++++++++++++++++++++++--------------
lib/usercopy.c | 30 ++++--------------------------
2 files changed, 28 insertions(+), 40 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 3064314f4832..2ebfce98b5cc 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -5,6 +5,7 @@
#include <linux/fault-inject-usercopy.h>
#include <linux/instrumented.h>
#include <linux/minmax.h>
+#include <linux/nospec.h>
#include <linux/sched.h>
#include <linux/thread_info.h>

@@ -138,13 +139,18 @@ __copy_to_user(void __user *to, const void *from, unsigned long n)
return raw_copy_to_user(to, from, n);
}

-#ifdef INLINE_COPY_FROM_USER
static inline __must_check unsigned long
-_copy_from_user(void *to, const void __user *from, unsigned long n)
+_inline_copy_from_user(void *to, const void __user *from, unsigned long n)
{
unsigned long res = n;
might_fault();
if (!should_fail_usercopy() && likely(access_ok(from, n))) {
+ /*
+ * Ensure that bad access_ok() speculation will not
+ * lead to nasty side effects *after* the copy is
+ * finished:
+ */
+ barrier_nospec();
instrument_copy_from_user_before(to, from, n);
res = raw_copy_from_user(to, from, n);
instrument_copy_from_user_after(to, from, n, res);
@@ -153,14 +159,11 @@ _copy_from_user(void *to, const void __user *from, unsigned long n)
memset(to + (n - res), 0, res);
return res;
}
-#else
extern __must_check unsigned long
_copy_from_user(void *, const void __user *, unsigned long);
-#endif

-#ifdef INLINE_COPY_TO_USER
static inline __must_check unsigned long
-_copy_to_user(void __user *to, const void *from, unsigned long n)
+_inline_copy_to_user(void __user *to, const void *from, unsigned long n)
{
might_fault();
if (should_fail_usercopy())
@@ -171,25 +174,32 @@ _copy_to_user(void __user *to, const void *from, unsigned long n)
}
return n;
}
-#else
extern __must_check unsigned long
_copy_to_user(void __user *, const void *, unsigned long);
-#endif

static __always_inline unsigned long __must_check
copy_from_user(void *to, const void __user *from, unsigned long n)
{
- if (check_copy_size(to, n, false))
- n = _copy_from_user(to, from, n);
- return n;
+ if (!check_copy_size(to, n, false))
+ return n;
+#ifdef INLINE_COPY_FROM_USER
+ return _inline_copy_from_user(to, from, n);
+#else
+ return _copy_from_user(to, from, n);
+#endif
}

static __always_inline unsigned long __must_check
copy_to_user(void __user *to, const void *from, unsigned long n)
{
- if (check_copy_size(from, n, true))
- n = _copy_to_user(to, from, n);
- return n;
+ if (!check_copy_size(from, n, true))
+ return n;
+
+#ifdef INLINE_COPY_TO_USER
+ return _inline_copy_to_user(to, from, n);
+#else
+ return _copy_to_user(to, from, n);
+#endif
}

#ifndef copy_mc_to_kernel
diff --git a/lib/usercopy.c b/lib/usercopy.c
index d29fe29c6849..de7f30618293 100644
--- a/lib/usercopy.c
+++ b/lib/usercopy.c
@@ -7,40 +7,18 @@

/* out-of-line parts */

-#ifndef INLINE_COPY_FROM_USER
+#if !defined(INLINE_COPY_FROM_USER) || defined(CONFIG_RUST)
unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
{
- unsigned long res = n;
- might_fault();
- if (!should_fail_usercopy() && likely(access_ok(from, n))) {
- /*
- * Ensure that bad access_ok() speculation will not
- * lead to nasty side effects *after* the copy is
- * finished:
- */
- barrier_nospec();
- instrument_copy_from_user_before(to, from, n);
- res = raw_copy_from_user(to, from, n);
- instrument_copy_from_user_after(to, from, n, res);
- }
- if (unlikely(res))
- memset(to + (n - res), 0, res);
- return res;
+ return _inline_copy_from_user(to, from, n);
}
EXPORT_SYMBOL(_copy_from_user);
#endif

-#ifndef INLINE_COPY_TO_USER
+#if !defined(INLINE_COPY_TO_USER) || defined(CONFIG_RUST)
unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
{
- might_fault();
- if (should_fail_usercopy())
- return n;
- if (likely(access_ok(to, n))) {
- instrument_copy_to_user(to, from, n);
- n = raw_copy_to_user(to, from, n);
- }
- return n;
+ return _inline_copy_to_user(to, from, n);
}
EXPORT_SYMBOL(_copy_to_user);
#endif

--
2.44.0.278.ge034bb2e1d-goog