Re: [PATCH] riscv: defconfig: Disable COMPAT_BRK

[Paul Walmsley <pjw@kernel.org>]

On Thu, 29 Oct 2026, Michael Ellerman wrote:

> COMPAT_BRK defaults to y, which disables brk (heap) randomisation by
> default (ie. randomize_va_space=1 by default) for compatibility with
> "ancient" binaries, in particular libc5 based binaries.
> 
> libc5 predates RISC-V, so there can't be any libc5 binaries for RISC-V.
> 
> COMPAT_BRK was introduced in 2008, commit 32a932332c8b
> ("brk randomization: introduce CONFIG_COMPAT_BRK"). But even then the
> only non-libc5 binaries mentioned as being broken were ~5 year old
> versions of emacs (see commit c1d171a00294 ("x86: randomize brk")).
> 
> Distro kernels for riscv64 also disable it, including Debian, Fedora,
> openSUSE and Ubuntu. So even if there were riscv binaries out there
> that rely on it, no mainstream distro would support them.
> 
> Most other architectures already disable COMPAT_BRK in their primary
> defconfigs, including arm64, x86_64, powerpc, s390, loongarch and
> sparc64, as do the riscv nommu defconfigs. It is also disabled in
> kernel/configs/hardening.config.
> 
> So disable COMPAT_BRK in the riscv defconfig so that brk is randomised
> by default, matching distro and other arch configs.
> 
> Signed-off-by: Michael Ellerman <mpe@kernel.org>

Thanks, queued for v7.4-rc.


- Paul