Re: [PATCH] linux: Do not allow slab caches to be merged

[Michael Tremer <michael.tremer@ipfire.org>]

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And there are no downsides to this whatsoever?

> On 1 Aug 2022, at 18:39, Peter Müller <peter.mueller(a)ipfire.org> wrote:
> 
> 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 Müller <peter.mueller(a)ipfire.org>
> ---
> 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/kernel.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=y
> # CONFIG_SLAB is not set
> CONFIG_SLUB=y
> # CONFIG_SLOB is not set
> -CONFIG_SLAB_MERGE_DEFAULT=y
> +# CONFIG_SLAB_MERGE_DEFAULT is not set
> CONFIG_SLAB_FREELIST_RANDOM=y
> CONFIG_SLAB_FREELIST_HARDENED=y
> CONFIG_SHUFFLE_PAGE_ALLOCATOR=y
> diff --git a/config/kernel/kernel.config.armv6l-ipfire b/config/kernel/kernel.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=y
> # CONFIG_SLAB is not set
> CONFIG_SLUB=y
> # CONFIG_SLOB is not set
> -CONFIG_SLAB_MERGE_DEFAULT=y
> +# CONFIG_SLAB_MERGE_DEFAULT is not set
> CONFIG_SLAB_FREELIST_RANDOM=y
> CONFIG_SLAB_FREELIST_HARDENED=y
> CONFIG_SHUFFLE_PAGE_ALLOCATOR=y
> diff --git a/config/kernel/kernel.config.riscv64-ipfire b/config/kernel/kernel.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=y
> # CONFIG_SLAB is not set
> CONFIG_SLUB=y
> # CONFIG_SLOB is not set
> -CONFIG_SLAB_MERGE_DEFAULT=y
> +# CONFIG_SLAB_MERGE_DEFAULT is not set
> CONFIG_SLAB_FREELIST_RANDOM=y
> CONFIG_SLAB_FREELIST_HARDENED=y
> CONFIG_SHUFFLE_PAGE_ALLOCATOR=y
> diff --git a/config/kernel/kernel.config.x86_64-ipfire b/config/kernel/kernel.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=y
> # CONFIG_SLAB is not set
> CONFIG_SLUB=y
> # CONFIG_SLOB is not set
> -CONFIG_SLAB_MERGE_DEFAULT=y
> +# CONFIG_SLAB_MERGE_DEFAULT is not set
> CONFIG_SLAB_FREELIST_RANDOM=y
> CONFIG_SLAB_FREELIST_HARDENED=y
> CONFIG_SHUFFLE_PAGE_ALLOCATOR=y
> -- 
> 2.35.3