4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mark Rutland <mark.rutland@xxxxxxx>
From: Robin Murphy <robin.murphy@xxxxxxx>
commit 4d8efc2d5ee4c9ccfeb29ee8afd47a8660d0c0ce upstream.
Similarly to x86, mitigate speculation past an access_ok() check by
masking the pointer against the address limit before use.
Even if we don't expect speculative writes per se, it is plausible that
a CPU may still speculate at least as far as fetching a cache line for
writing, hence we also harden put_user() and clear_user() for peace of
mind.
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> [v4.9 backport]
Tested-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/uaccess.h | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -129,6 +129,26 @@ static inline unsigned long __range_ok(u
" .popsection\n"
/*
+ * Sanitise a uaccess pointer such that it becomes NULL if above the
+ * current addr_limit.
+ */
+#define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
+static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
+{
+ void __user *safe_ptr;
+
+ asm volatile(
+ " bics xzr, %1, %2\n"
+ " csel %0, %1, xzr, eq\n"
+ : "=&r" (safe_ptr)
+ : "r" (ptr), "r" (current_thread_info()->addr_limit)
+ : "cc");
+
+ csdb();
+ return safe_ptr;
+}
+
+/*
* The "__xxx" versions of the user access functions do not verify the address
* space - it must have been done previously with a separate "access_ok()"
* call.
@@ -202,7 +222,7 @@ do { \
__typeof__(*(ptr)) __user *__p = (ptr); \
might_fault(); \
access_ok(VERIFY_READ, __p, sizeof(*__p)) ? \
- __get_user((x), __p) : \
+ __p = uaccess_mask_ptr(__p), __get_user((x), __p) : \
((x) = 0, -EFAULT); \
})
@@ -270,7 +290,7 @@ do { \
__typeof__(*(ptr)) __user *__p = (ptr); \
might_fault(); \
access_ok(VERIFY_WRITE, __p, sizeof(*__p)) ? \
- __put_user((x), __p) : \
+ __p = uaccess_mask_ptr(__p), __put_user((x), __p) : \
-EFAULT; \
})
@@ -331,7 +351,7 @@ static inline unsigned long __must_check
static inline unsigned long __must_check clear_user(void __user *to, unsigned long n)
{
if (access_ok(VERIFY_WRITE, to, n))
- n = __clear_user(to, n);
+ n = __clear_user(__uaccess_mask_ptr(to), n);
return n;
}