Messages in this thread | | | Date | Tue, 9 Feb 2021 12:24:23 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH] ubsan: Require GCC-8+ or Clang to use UBSAN |
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On Mon, Jan 18, 2021 at 11:53:37AM -0600, Josh Poimboeuf wrote: > On Thu, Jan 14, 2021 at 02:09:28PM +0300, Andrey Ryabinin wrote: > > > > > > On 1/14/21 1:59 PM, Peter Zijlstra wrote: > > > On Mon, Jan 04, 2021 at 04:13:17PM +0100, Peter Zijlstra wrote: > > >> On Tue, Dec 22, 2020 at 11:04:54PM -0600, Josh Poimboeuf wrote: > > >>> GCC 7 has a known bug where UBSAN ignores '-fwrapv' and generates false > > >>> signed-overflow-UB warnings. The type mismatch between 'i' and > > >>> 'nr_segs' in copy_compat_iovec_from_user() is causing such a warning, > > >>> which also happens to violate uaccess rules: > > >>> > > >>> lib/iov_iter.o: warning: objtool: iovec_from_user()+0x22d: call to __ubsan_handle_add_overflow() with UACCESS enabled > > >>> > > >>> Fix it by making the variable types match. > > >>> > > >>> This is similar to a previous commit: > > >>> > > >>> 29da93fea3ea ("mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions") > > >> > > >> Maybe it's time we make UBSAN builds depend on GCC-8+ ? > > > > > > --- > > > Subject: ubsan: Require GCC-8+ or Clang to use UBSAN > > > > > > Just like how we require GCC-8.2 for KASAN due to compiler bugs, require > > > a sane version of GCC for UBSAN. > > > > > > Specifically, before GCC-8 UBSAN doesn't respect -fwrapv and thinks > > > signed arithmetic is buggered. > > > > > > > Actually removing CONFIG_UBSAN_SIGNED_OVERFLOW would give us the same > > effect without restricting GCC versions. > > Is that preferable? Always happy to remove code, just need some > justification behind it.
Andrey,
Is Peter's patch acceptable or do you want to do something else?
-- Josh
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