> On Apr 23, 2019, at 1:24 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > >> On Fri, Apr 19, 2019 at 09:36:46PM -0700, Randy Dunlap wrote: >>> On 4/19/19 2:53 PM, akpm@xxxxxxxxxxxxxxxxxxxx wrote: >>> The mm-of-the-moment snapshot 2019-04-19-14-53 has been uploaded to >>> >>> http://www.ozlabs.org/~akpm/mmotm/ >>> >>> mmotm-readme.txt says >>> >>> README for mm-of-the-moment: >>> >>> http://www.ozlabs.org/~akpm/mmotm/ >>> >>> This is a snapshot of my -mm patch queue. Uploaded at random hopefully >>> more than once a week. >> >> on x86_64: >> >> CC lib/strncpy_from_user.o >> lib/strncpy_from_user.o: warning: objtool: strncpy_from_user()+0x315: call to __ubsan_handle_add_overflow() with UACCESS enabled >> CC lib/strnlen_user.o >> lib/strnlen_user.o: warning: objtool: strnlen_user()+0x337: call to __ubsan_handle_sub_overflow() with UACCESS enabled > > Lemme guess, you're using GCC < 8 ? That had a bug where UBSAN > considered signed overflow UB when using -fno-strict-overflow or > -fwrapv. > > Now, we could of course allow this symbol, but I found only the below > was required to make allyesconfig build without issue. > > Andy, Linus? > > (note: the __put_user thing is from this one: > > drivers/gpu/drm/i915/i915_gem_execbuffer.c: if (unlikely(__put_user(offset, &urelocs[r-stack].presumed_offset))) { > > where (ptr) ends up non-trivial due to UBSAN) > > --- > > diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h > index 22ba683afdc2..c82abd6e4ca3 100644 > --- a/arch/x86/include/asm/uaccess.h > +++ b/arch/x86/include/asm/uaccess.h > @@ -427,10 +427,11 @@ do { \ > ({ \ > __label__ __pu_label; \ > int __pu_err = -EFAULT; \ > - __typeof__(*(ptr)) __pu_val; \ > - __pu_val = x; \ > + __typeof__(*(ptr)) __pu_val = (x); \ > + __typeof__(ptr) __pu_ptr = (ptr); \ Hmm. I wonder if this forces the address calculation to be done before STAC, which means that gcc can’t use mov ..., %gs:(fancy stuff). It probably depends on how clever the optimizer is. Have you looked at the generated code? Other than that, it seems reasonable to me. > + __typeof__(size) __pu_size = (size); \ > __uaccess_begin(); \ > - __put_user_size(__pu_val, (ptr), (size), __pu_label); \ > + __put_user_size(__pu_val, __pu_ptr, __pu_size, __pu_label); \ > __pu_err = 0; \ > __pu_label: \ > __uaccess_end(); \ > diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c > index 58eacd41526c..07045bc4872e 100644 > --- a/lib/strncpy_from_user.c > +++ b/lib/strncpy_from_user.c > @@ -26,7 +26,7 @@ > static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max) > { > const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; > - long res = 0; > + unsigned long res = 0; > > /* > * Truncate 'max' to the user-specified limit, so that > diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c > index 1c1a1b0e38a5..0729378ad3e9 100644 > --- a/lib/strnlen_user.c > +++ b/lib/strnlen_user.c > @@ -28,7 +28,7 @@ > static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max) > { > const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; > - long align, res = 0; > + unsigned long align, res = 0; > unsigned long c; > > /* >
