On Wed, Apr 18, 2018 at 08:53:12PM +0200, Andrey Konovalov wrote:
> @@ -238,12 +239,15 @@ static inline void uaccess_enable_not_uao(void)
> /*
> * Sanitise a uaccess pointer such that it becomes NULL if above the
> * current addr_limit.
> + * Also untag user pointers that have the top byte tag set.
> */
> #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;
>
> + ptr = untagged_addr(ptr);
> +
> asm volatile(
> " bics xzr, %1, %2\n"
> " csel %0, %1, xzr, eq\n"
First of all, passing a tagged user pointer throughout the kernel is
safe with uaccess routines but not suitable for find_vma() etc.
With this change, we may have an inconsistent behaviour on the tag
masking, depending on whether the entry code uses __uaccess_mask_ptr()
or not. We could preserve the tag with something like:
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index e66b0fca99c2..ed15bfcbd797 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -244,10 +244,11 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
void __user *safe_ptr;
asm volatile(
- " bics xzr, %1, %2\n"
+ " bics xzr, %3, %2\n"
" csel %0, %1, xzr, eq\n"
: "=&r" (safe_ptr)
- : "r" (ptr), "r" (current_thread_info()->addr_limit)
+ : "r" (ptr), "r" (current_thread_info()->addr_limit),
+ "r" (untagged_addr(ptr))
: "cc");
csdb();
--
Catalin
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