From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter =?utf-8?q?M=C3=BCller?= To: development@lists.ipfire.org Subject: Re: [PATCH] linux: Do not allow slab caches to be merged Date: Tue, 02 Aug 2022 09:50:11 +0000 Message-ID: <8d253796-8a1b-9581-9891-7e6f50de10ed@ipfire.org> In-Reply-To: <6477003F-E0BE-41D3-8401-C3002A933230@ipfire.org> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="===============2262956953569846932==" List-Id: --===============2262956953569846932== Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Hello Michael, aside from increased kernel memory fragmentation, none I am aware of. Thanks, and best regards, Peter M=C3=BCller > And there are no downsides to this whatsoever? >=20 >> On 1 Aug 2022, at 18:39, Peter M=C3=BCller wr= ote: >> >> From the kernel documentation: >> >>> For reduced kernel memory fragmentation, slab caches can be >>> merged when they share the same size and other characteristics. >>> This carries a risk of kernel heap overflows being able to >>> overwrite objects from merged caches (and more easily control >>> cache layout), which makes such heap attacks easier to exploit >>> by attackers. By keeping caches unmerged, these kinds of exploits >>> can usually only damage objects in the same cache. [...] >> >> Thus, it is more sane to leave slab merging disabled. KSPP and ClipOS >> recommend this as well. >> >> Signed-off-by: Peter M=C3=BCller >> --- >> config/kernel/kernel.config.aarch64-ipfire | 2 +- >> config/kernel/kernel.config.armv6l-ipfire | 2 +- >> config/kernel/kernel.config.riscv64-ipfire | 2 +- >> config/kernel/kernel.config.x86_64-ipfire | 2 +- >> 4 files changed, 4 insertions(+), 4 deletions(-) >> >> diff --git a/config/kernel/kernel.config.aarch64-ipfire b/config/kernel/ke= rnel.config.aarch64-ipfire >> index 9232335ff..023c3d5aa 100644 >> --- a/config/kernel/kernel.config.aarch64-ipfire >> +++ b/config/kernel/kernel.config.aarch64-ipfire >> @@ -247,7 +247,7 @@ CONFIG_VM_EVENT_COUNTERS=3Dy >> # CONFIG_SLAB is not set >> CONFIG_SLUB=3Dy >> # CONFIG_SLOB is not set >> -CONFIG_SLAB_MERGE_DEFAULT=3Dy >> +# CONFIG_SLAB_MERGE_DEFAULT is not set >> CONFIG_SLAB_FREELIST_RANDOM=3Dy >> CONFIG_SLAB_FREELIST_HARDENED=3Dy >> CONFIG_SHUFFLE_PAGE_ALLOCATOR=3Dy >> diff --git a/config/kernel/kernel.config.armv6l-ipfire b/config/kernel/ker= nel.config.armv6l-ipfire >> index dc0aee51b..b4587826e 100644 >> --- a/config/kernel/kernel.config.armv6l-ipfire >> +++ b/config/kernel/kernel.config.armv6l-ipfire >> @@ -250,7 +250,7 @@ CONFIG_VM_EVENT_COUNTERS=3Dy >> # CONFIG_SLAB is not set >> CONFIG_SLUB=3Dy >> # CONFIG_SLOB is not set >> -CONFIG_SLAB_MERGE_DEFAULT=3Dy >> +# CONFIG_SLAB_MERGE_DEFAULT is not set >> CONFIG_SLAB_FREELIST_RANDOM=3Dy >> CONFIG_SLAB_FREELIST_HARDENED=3Dy >> CONFIG_SHUFFLE_PAGE_ALLOCATOR=3Dy >> diff --git a/config/kernel/kernel.config.riscv64-ipfire b/config/kernel/ke= rnel.config.riscv64-ipfire >> index 0801f4389..fb7cda4dd 100644 >> --- a/config/kernel/kernel.config.riscv64-ipfire >> +++ b/config/kernel/kernel.config.riscv64-ipfire >> @@ -230,7 +230,7 @@ CONFIG_VM_EVENT_COUNTERS=3Dy >> # CONFIG_SLAB is not set >> CONFIG_SLUB=3Dy >> # CONFIG_SLOB is not set >> -CONFIG_SLAB_MERGE_DEFAULT=3Dy >> +# CONFIG_SLAB_MERGE_DEFAULT is not set >> CONFIG_SLAB_FREELIST_RANDOM=3Dy >> CONFIG_SLAB_FREELIST_HARDENED=3Dy >> CONFIG_SHUFFLE_PAGE_ALLOCATOR=3Dy >> diff --git a/config/kernel/kernel.config.x86_64-ipfire b/config/kernel/ker= nel.config.x86_64-ipfire >> index 40975b5fc..d3792cbb7 100644 >> --- a/config/kernel/kernel.config.x86_64-ipfire >> +++ b/config/kernel/kernel.config.x86_64-ipfire >> @@ -270,7 +270,7 @@ CONFIG_VM_EVENT_COUNTERS=3Dy >> # CONFIG_SLAB is not set >> CONFIG_SLUB=3Dy >> # CONFIG_SLOB is not set >> -CONFIG_SLAB_MERGE_DEFAULT=3Dy >> +# CONFIG_SLAB_MERGE_DEFAULT is not set >> CONFIG_SLAB_FREELIST_RANDOM=3Dy >> CONFIG_SLAB_FREELIST_HARDENED=3Dy >> CONFIG_SHUFFLE_PAGE_ALLOCATOR=3Dy >> --=20 >> 2.35.3 >=20 --===============2262956953569846932==--