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[203.219.139.206]) by smtp.gmail.com with ESMTPSA id h8sm5230340pgj.26.2021.12.09.02.43.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Dec 2021 02:43:38 -0800 (PST) Date: Thu, 09 Dec 2021 20:43:32 +1000 From: Nicholas Piggin Subject: Re: [PATCH v4 09/10] powerpc/mm: Convert to default topdown mmap layout To: "alex@ghiti.fr" , Benjamin Herrenschmidt , Christophe Leroy , Michael Ellerman , Paul Mackerras Cc: "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linuxppc-dev@lists.ozlabs.org" References: <1639044621.jeow25j0pr.astroid@bobo.none> <360e2a3e-63c6-3ce2-f481-695ad0ec4880@csgroup.eu> In-Reply-To: <360e2a3e-63c6-3ce2-f481-695ad0ec4880@csgroup.eu> MIME-Version: 1.0 Message-Id: <1639046542.qkwu4mjtew.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Excerpts from Christophe Leroy's message of December 9, 2021 8:22 pm: >=20 >=20 > Le 09/12/2021 =C3=A0 11:15, Nicholas Piggin a =C3=A9crit=C2=A0: >> Excerpts from Christophe Leroy's message of December 9, 2021 3:18 am: >>> Select CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and >>> remove arch/powerpc/mm/mmap.c >>> >>> This change provides standard randomisation of mmaps. >>> >>> See commit 8b8addf891de ("x86/mm/32: Enable full randomization on i386 >>> and X86_32") for all the benefits of mmap randomisation. >>=20 >> The justification seems pretty reasonable. >>=20 >>> >>> Comparison between powerpc implementation and the generic one: >>> - mmap_is_legacy() is identical. >>> - arch_mmap_rnd() does exactly the same allthough it's written >>> slightly differently. >>> - MIN_GAP and MAX_GAP are identical. >>> - mmap_base() does the same but uses STACK_RND_MASK which provides >>> the same values as stack_maxrandom_size(). >>> - arch_pick_mmap_layout() is almost identical. The only difference >>> is that it also adds the random factor to mm->mmap_base in legacy mode. >>> >>> That last point is what provides the standard randomisation of mmaps. >>=20 >> Thanks for describing it. Could you add random_factor to mmap_base for >> the legacy path for powerpc as a 2-line change that adds the legacy >> randomisation. And then this bigger patch would be closer to a no-op. >>=20 >=20 > You mean you would like to see the following patch before doing the=20 > convert ? >=20 > https://patchwork.ozlabs.org/project/linuxppc-dev/patch/7dabf1cbde67a346a= 187881d4f0bd17347e0334a.1533732583.git.christophe.leroy@c-s.fr/ Yes. Thanks, Nick