Re: [PATCH 00/10] raise minimum GCC version to 5.1

[PATCH 00/10] raise minimum GCC version to 5.1 · Nick Desaulniers <hidden> · 2021-09-10
[PATCH 01/10] Documentation: raise minimum supported version of GCC to 5.1 · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 01/10] Documentation: raise minimum supported version of GCC to 5.1 · Nathan Chancellor <nathan@kernel.org> · 2021-09-10
Re: [PATCH 01/10] Documentation: raise minimum supported version of GCC to 5.1 · Nick Desaulniers <hidden> · 2021-09-11
Re: [PATCH 01/10] Documentation: raise minimum supported version of GCC to 5.1 · Kees Cook <hidden> · 2021-09-13
[PATCH 03/10] mm/ksm: remove old GCC 4.9+ check · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 03/10] mm/ksm: remove old GCC 4.9+ check · Nathan Chancellor <nathan@kernel.org> · 2021-09-11
Re: [PATCH 03/10] mm/ksm: remove old GCC 4.9+ check · Kees Cook <hidden> · 2021-09-13
[PATCH 02/10] compiler.h: drop fallback overflow checkers · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 02/10] compiler.h: drop fallback overflow checkers · Nathan Chancellor <nathan@kernel.org> · 2021-09-11
Re: [PATCH 02/10] compiler.h: drop fallback overflow checkers · Nick Desaulniers <hidden> · 2021-09-14
Re: [PATCH 02/10] compiler.h: drop fallback overflow checkers · Nathan Chancellor <nathan@kernel.org> · 2021-09-14
Re: [PATCH 02/10] compiler.h: drop fallback overflow checkers · Kees Cook <hidden> · 2021-09-13
[PATCH 04/10] Kconfig.debug: drop GCC 5+ version check for DWARF5 · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 04/10] Kconfig.debug: drop GCC 5+ version check for DWARF5 · Nathan Chancellor <nathan@kernel.org> · 2021-09-11
Re: [PATCH 04/10] Kconfig.debug: drop GCC 5+ version check for DWARF5 · Kees Cook <hidden> · 2021-09-13
[PATCH 05/10] riscv: remove Kconfig check for GCC version for ARCH_RV64I · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 05/10] riscv: remove Kconfig check for GCC version for ARCH_RV64I · Nathan Chancellor <nathan@kernel.org> · 2021-09-11
Re: [PATCH 05/10] riscv: remove Kconfig check for GCC version for ARCH_RV64I · Kees Cook <hidden> · 2021-09-13
Re: [PATCH 05/10] riscv: remove Kconfig check for GCC version for ARCH_RV64I · Palmer Dabbelt <palmer@dabbelt.com> · 2021-10-05
Re: [PATCH 05/10] riscv: remove Kconfig check for GCC version for ARCH_RV64I · Kees Cook <hidden> · 2021-10-05
Re: [PATCH 05/10] riscv: remove Kconfig check for GCC version for ARCH_RV64I · Palmer Dabbelt <palmer@dabbelt.com> · 2021-10-05
[PATCH 06/10] powerpc: remove GCC version check for UPD_CONSTR · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 06/10] powerpc: remove GCC version check for UPD_CONSTR · Nathan Chancellor <nathan@kernel.org> · 2021-09-10
Re: [PATCH 06/10] powerpc: remove GCC version check for UPD_CONSTR · Michael Ellerman <mpe@ellerman.id.au> · 2021-09-11
Re: [PATCH 06/10] powerpc: remove GCC version check for UPD_CONSTR · Christophe Leroy <hidden> · 2021-09-11
[PATCH 07/10] arm64: remove GCC version check for ARCH_SUPPORTS_INT128 · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 07/10] arm64: remove GCC version check for ARCH_SUPPORTS_INT128 · Nathan Chancellor <nathan@kernel.org> · 2021-09-11
Re: [PATCH 07/10] arm64: remove GCC version check for ARCH_SUPPORTS_INT128 · Kees Cook <hidden> · 2021-09-13
Re: [PATCH 07/10] arm64: remove GCC version check for ARCH_SUPPORTS_INT128 · Catalin Marinas <catalin.marinas@arm.com> · 2021-09-16
[PATCH 08/10] Makefile: drop GCC < 5 -fno-var-tracking-assignments workaround · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 08/10] Makefile: drop GCC < 5 -fno-var-tracking-assignments workaround · Nathan Chancellor <nathan@kernel.org> · 2021-09-11
Re: [PATCH 08/10] Makefile: drop GCC < 5 -fno-var-tracking-assignments workaround · Kees Cook <hidden> · 2021-09-13
[PATCH 10/10] vmlinux.lds.h: remove old check for GCC 4.9 · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 10/10] vmlinux.lds.h: remove old check for GCC 4.9 · Nathan Chancellor <nathan@kernel.org> · 2021-09-10
Re: [PATCH 10/10] vmlinux.lds.h: remove old check for GCC 4.9 · Nick Desaulniers <hidden> · 2021-09-14
Re: [PATCH 10/10] vmlinux.lds.h: remove old check for GCC 4.9 · Kees Cook <hidden> · 2021-09-13
[PATCH 09/10] compiler-gcc.h: drop checks for older GCC versions · Nick Desaulniers <hidden> · 2021-09-10
Re: [PATCH 09/10] compiler-gcc.h: drop checks for older GCC versions · Nathan Chancellor <nathan@kernel.org> · 2021-09-11
Re: [PATCH 09/10] compiler-gcc.h: drop checks for older GCC versions · Kees Cook <hidden> · 2021-09-13
Re: [PATCH 00/10] raise minimum GCC version to 5.1 · Kees Cook <hidden> · 2021-09-11
Re: [PATCH 00/10] raise minimum GCC version to 5.1 · Michael Ellerman <mpe@ellerman.id.au> · 2021-09-11
Re: [PATCH 00/10] raise minimum GCC version to 5.1 · Pavel Machek <hidden> · 2021-09-13
Re: [PATCH 00/10] raise minimum GCC version to 5.1 · Kees Cook <hidden> · 2021-09-13
Re: [PATCH 00/10] raise minimum GCC version to 5.1 · Arnd Bergmann <arnd@kernel.org> · 2021-09-13

From: Kees Cook <hidden>
Date: 2021-09-13 16:20:36
Also in: lkml

On Mon, Sep 13, 2021 at 11:49:48AM +0200, Pavel Machek wrote:

Hi!

quoted

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.

Please don't. gcc 4.9.2 is still in use here.

Plus, someone will want to prevent overflow in -stable, too, and you
can't really raise gcc version there.

These changes won't go to prior stable kernels.

-- 
Kees Cook

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