Messages in this thread Patch in this message | | | Date | Thu, 14 Jan 2021 11:59:01 +0100 | From | Peter Zijlstra <> | Subject | [PATCH] ubsan: Require GCC-8+ or Clang to use UBSAN |
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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.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- lib/Kconfig.ubsan | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan index 8b635fd75fe4..acc3df62460e 100644 --- a/lib/Kconfig.ubsan +++ b/lib/Kconfig.ubsan @@ -2,8 +2,13 @@ config ARCH_HAS_UBSAN_SANITIZE_ALL bool +# UBSAN prior to GCC-8 gets -fwrapv wrong, we rely on that +config UBSAN_SANE + def_bool !CC_IS_GCC || GCC_VERSION >= 80000 + menuconfig UBSAN bool "Undefined behaviour sanity checker" + depends on UBSAN_SANE help This option enables the Undefined Behaviour sanity checker. Compile-time instrumentation is used to detect various undefined
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