From: Robin Murphy robin.murphy@arm.com
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@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Mark Rutland mark.rutland@arm.com [v4.9 backport] --- arch/arm64/include/asm/uaccess.h | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index 0f05ba51531c..a9db051b967f 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -129,6 +129,26 @@ static inline unsigned long __range_ok(unsigned long addr, unsigned long size) " .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 copy_in_user(void __user *to, const voi 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; }