linux-kernel - Re: [PATCH 2/2] x86/modules: Make x86 allocs to flush when free

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Message-ID: <CALCETrU+skBS0r6WtkwwMZJvb3s2vWB-JmDeZtVWV8pOkxKojQ@mail.gmail.com>
Date:   Wed, 28 Nov 2018 17:40:53 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Will Deacon <will.deacon@....com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, jeyu@...nel.org,
        Network Development <netdev@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jann Horn <jannh@...gle.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Dock, Deneen T" <deneen.t.dock@...el.com>
Subject: Re: [PATCH 2/2] x86/modules: Make x86 allocs to flush when free

> On Nov 27, 2018, at 4:07 PM, Rick Edgecombe <rick.p.edgecombe@...el.com> wrote:
>
> Change the module allocations to flush before freeing the pages.
>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---
> arch/x86/kernel/module.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
> index b052e883dd8c..1694daf256b3 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -87,8 +87,8 @@ void *module_alloc(unsigned long size)
>    p = __vmalloc_node_range(size, MODULE_ALIGN,
>                    MODULES_VADDR + get_module_load_offset(),
>                    MODULES_END, GFP_KERNEL,
> -                    PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
> -                    __builtin_return_address(0));
> +                    PAGE_KERNEL_EXEC, VM_IMMEDIATE_UNMAP,
> +                    NUMA_NO_NODE, __builtin_return_address(0));

Hmm. How awful is the resulting performance for heavy eBPF users?  I’m
wondering if the JIT will need some kind of cache to reuse
allocations.

>    if (p && (kasan_module_alloc(p, size) < 0)) {
>        vfree(p);
>        return NULL;
> --
> 2.17.1
>