On Wed, Aug 28, 2019 at 03:01:34PM -0500, Josh Poimboeuf wrote: > On Wed, Aug 28, 2019 at 10:56:25AM -0700, Randy Dunlap wrote: > > >> drivers/xen/gntdev.o: warning: objtool: gntdev_copy()+0x229: call to __ubsan_handle_out_of_bounds() with UACCESS enabled > > > > > > Easy one :-) > > > > > > diff --git a/tools/objtool/check.c b/tools/objtool/check.c > > > index 0c8e17f946cd..6a935ab93149 100644 > > > --- a/tools/objtool/check.c > > > +++ b/tools/objtool/check.c > > > @@ -483,6 +483,7 @@ static const char *uaccess_safe_builtin[] = { > > > "ubsan_type_mismatch_common", > > > "__ubsan_handle_type_mismatch", > > > "__ubsan_handle_type_mismatch_v1", > > > + "__ubsan_handle_out_of_bounds", > > > /* misc */ > > > "csum_partial_copy_generic", > > > "__memcpy_mcsafe", > > > > > > > > > then I get this one: > > > > lib/ubsan.o: warning: objtool: __ubsan_handle_out_of_bounds()+0x5d: call to ubsan_prologue() with UACCESS enabled > > And of course I jinxed it by calling it easy. > > Peter, how do you want to handle this? > > Should we just disable UACCESS checking in lib/ubsan.c? No, that is actually unsafe and could break things (as would you patch above). I'm thinking the below patch ought to cure things: --- Subject: x86/uaccess: Don't leak the AC flags into __get_user() argument evalidation Identical to __put_user(); the __get_user() argument evalution will too leak UBSAN crud into the __uaccess_begin() / __uaccess_end() region. While uncommon this was observed to happen for: drivers/xen/gntdev.c: if (__get_user(old_status, batch->status[i])) where UBSAN added array bound checking. This complements commit: 6ae865615fc4 ("x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation") Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Cc: luto@xxxxxxxxxx --- arch/x86/include/asm/uaccess.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 9c4435307ff8..35c225ede0e4 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -444,8 +444,10 @@ __pu_label: \ ({ \ int __gu_err; \ __inttype(*(ptr)) __gu_val; \ + __typeof__(ptr) __gu_ptr = (ptr); \ + __typeof__(size) __gu_size = (size); \ __uaccess_begin_nospec(); \ - __get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT); \ + __get_user_size(__gu_val, __gu_ptr, __gu_size, __gu_err, -EFAULT); \ __uaccess_end(); \ (x) = (__force __typeof__(*(ptr)))__gu_val; \ __builtin_expect(__gu_err, 0); \