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From: Kees Cook <keescook@chromium.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Nathan Chancellor <nathan@kernel.org>,
Masahiro Yamada <masahiroy@kernel.org>,
Joe Perches <joe@perches.com>, Arnd Bergmann <arnd@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
llvm@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] raise minimum GCC version to 5.1
Date: Fri, 10 Sep 2021 19:19:50 -0700 [thread overview]
Message-ID: <202109101917.5BA95B87E0@keescook> (raw)
In-Reply-To: <20210910234047.1019925-1-ndesaulniers@google.com>
On Fri, Sep 10, 2021 at 04:40:37PM -0700, Nick Desaulniers wrote:
> commit fad7cd3310db ("nbd: add the check to prevent overflow in
> __nbd_ioctl()")
>
> raised an issue from the fallback helpers added in
>
> commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and add fallback code")
>
> Specifically, the helpers for checking whether the results of a
> multiplication overflowed (__unsigned_mul_overflow,
> __signed_add_overflow) use the division operator when
> !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW. This is problematic for 64b
> operands on 32b hosts.
>
> Also, because the macro is type agnostic, it is very difficult to write
> a similarly type generic macro that dispatches to one of:
> * div64_s64
> * div64_u64
> * div_s64
> * div_u64
Given that it's all compile-time type-aware goo, this isn't so bad. The
gist[1] you linked off the bug report is pretty close. Needs some
bikeshedding. ;)
> Raising the minimum supported versions allows us to remove all of the
> fallback helpers for !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW, instead
> dispatching the compiler builtins.
>
> arm64 has already raised the minimum supported GCC version to 5.1, do
> this for all targets now. See the link below for the previous
> discussion.
That said, I'd much prefer raising the minimum GCC -- no one appears
to actually be building on 4.9 -- there are close to 200 errors (neé
warnings) on x86_64 allmodconfig there currently.
-Kees
[1] https://gist.github.com/nickdesaulniers/2479818f4983bbf2d688cebbab435863
--
Kees Cook
next prev parent reply other threads:[~2021-09-11 2:19 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-10 23:40 [PATCH 00/10] raise minimum GCC version to 5.1 Nick Desaulniers
2021-09-10 23:40 ` [PATCH 01/10] Documentation: raise minimum supported version of GCC " Nick Desaulniers
2021-09-10 23:55 ` Nathan Chancellor
2021-09-11 0:16 ` Nick Desaulniers
2021-09-13 16:22 ` Kees Cook
2021-09-10 23:40 ` [PATCH 02/10] compiler.h: drop fallback overflow checkers Nick Desaulniers
2021-09-11 0:04 ` Nathan Chancellor
2021-09-14 15:33 ` Nick Desaulniers
2021-09-14 16:04 ` Nathan Chancellor
2021-09-13 16:21 ` Kees Cook
2021-09-10 23:40 ` [PATCH 03/10] mm/ksm: remove old GCC 4.9+ check Nick Desaulniers
2021-09-11 0:07 ` Nathan Chancellor
2021-09-13 16:22 ` Kees Cook
2021-09-10 23:40 ` [PATCH 04/10] Kconfig.debug: drop GCC 5+ version check for DWARF5 Nick Desaulniers
2021-09-11 0:08 ` Nathan Chancellor
2021-09-13 16:23 ` Kees Cook
2021-09-10 23:40 ` [PATCH 05/10] riscv: remove Kconfig check for GCC version for ARCH_RV64I Nick Desaulniers
2021-09-11 0:09 ` Nathan Chancellor
2021-09-13 16:23 ` Kees Cook
2021-10-05 0:40 ` Palmer Dabbelt
2021-10-05 0:50 ` Kees Cook
2021-10-05 0:57 ` Palmer Dabbelt
2021-09-10 23:40 ` [PATCH 06/10] powerpc: remove GCC version check for UPD_CONSTR Nick Desaulniers
2021-09-10 23:48 ` Nathan Chancellor
2021-09-11 10:43 ` Michael Ellerman
2021-09-11 15:34 ` Christophe Leroy
2021-09-10 23:40 ` [PATCH 07/10] arm64: remove GCC version check for ARCH_SUPPORTS_INT128 Nick Desaulniers
2021-09-11 0:10 ` Nathan Chancellor
2021-09-13 16:25 ` Kees Cook
2021-09-16 13:23 ` Catalin Marinas
2021-09-10 23:40 ` [PATCH 08/10] Makefile: drop GCC < 5 -fno-var-tracking-assignments workaround Nick Desaulniers
2021-09-11 0:11 ` Nathan Chancellor
2021-09-13 16:25 ` Kees Cook
2021-09-10 23:40 ` [PATCH 09/10] compiler-gcc.h: drop checks for older GCC versions Nick Desaulniers
2021-09-11 0:12 ` Nathan Chancellor
2021-09-13 16:26 ` Kees Cook
2021-09-10 23:40 ` [PATCH 10/10] vmlinux.lds.h: remove old check for GCC 4.9 Nick Desaulniers
2021-09-10 23:50 ` Nathan Chancellor
2021-09-14 15:21 ` Nick Desaulniers
2021-09-13 16:28 ` Kees Cook
2021-09-11 2:19 ` Kees Cook [this message]
2021-09-11 10:42 ` [PATCH 00/10] raise minimum GCC version to 5.1 Michael Ellerman
2021-09-13 9:49 ` Pavel Machek
2021-09-13 16:20 ` Kees Cook
2021-09-13 11:27 ` Arnd Bergmann
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