Messages in this thread Patch in this message | | | Date | Thu, 10 Oct 2019 02:56:06 +0100 | From | Al Viro <> | Subject | Re: [PATCH] xtensa: fix {get,put}_user() for 64bit values |
| |
On Wed, Oct 09, 2019 at 06:38:12PM -0700, Max Filippov wrote:
> There's also the following code in the callers of this macro, e.g. in > __get_user_nocheck: > > long __gu_err, __gu_val; \ > __get_user_size(__gu_val, (ptr), (size), __gu_err); \ > (x) = (__force __typeof__(*(ptr)))__gu_val; \ > > the last line is important for sizes 1..4, because it takes care of > sign extension of the value loaded by the assembly. > At the same time the first line doesn't make sense for the size 8 > as it will result in value truncation.
Right you are...
> + long __gu_err; \ > + __typeof__(*(ptr) + 0) __gu_val; \
What would __u64 __gu_val; end up with for smaller sizes? I don't have xtensa cross-toolchain at the moment, so I can't check it easily; what does =r constraint generate in such case?
Another thing is, you want to zero it on failure, to avoid an uninitialized value ending up someplace interesting....
> @@ -198,7 +200,7 @@ do { > \ > case 1: __get_user_asm(x, ptr, retval, 1, "l8ui", __cb); break;\ > case 2: __get_user_asm(x, ptr, retval, 2, "l16ui", __cb); break;\ > case 4: __get_user_asm(x, ptr, retval, 4, "l32i", __cb); break;\ > - case 8: retval = __copy_from_user(&x, ptr, 8); break; \ > + case 8: retval = __copy_from_user(&x, ptr, 8) ? -EFAULT : 0; > break; \ > default: (x) = __get_user_bad(); \ > } \ > } while (0) > > Here __typeof__(*(ptr) + 0) makes enough room for all cases > in the __get_user_size and the "+0" part takes care of pointers > to const data.
| |