linux-kernel - Re: [PATCH v3 04/13] mm/execmem, arch: convert remaining overrides of module

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Date:   Tue, 7 Nov 2023 10:44:47 +0000
From:   Will Deacon <will@...nel.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Björn Töpel <bjorn@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "David S. Miller" <davem@...emloft.net>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Helge Deller <deller@....de>,
        Huacai Chen <chenhuacai@...nel.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nadav Amit <nadav.amit@...il.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Puranjay Mohan <puranjay12@...il.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Russell King <linux@...linux.org.uk>,
        Song Liu <song@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>, bpf@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-modules@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev,
        netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v3 04/13] mm/execmem, arch: convert remaining overrides
 of module_alloc to execmem

On Mon, Oct 30, 2023 at 09:00:53AM +0200, Mike Rapoport wrote:
> On Thu, Oct 26, 2023 at 11:24:39AM +0100, Will Deacon wrote:
> > On Thu, Oct 26, 2023 at 11:58:00AM +0300, Mike Rapoport wrote:
> > > On Mon, Oct 23, 2023 at 06:14:20PM +0100, Will Deacon wrote:
> > > > On Mon, Sep 18, 2023 at 10:29:46AM +0300, Mike Rapoport wrote:
> > > > > diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
> > > > > index dd851297596e..cd6320de1c54 100644
> > > > > --- a/arch/arm64/kernel/module.c
> > > > > +++ b/arch/arm64/kernel/module.c
> 
> ...
> 
> > > > > -	if (module_direct_base) {
> > > > > -		p = __vmalloc_node_range(size, MODULE_ALIGN,
> > > > > -					 module_direct_base,
> > > > > -					 module_direct_base + SZ_128M,
> > > > > -					 GFP_KERNEL | __GFP_NOWARN,
> > > > > -					 PAGE_KERNEL, 0, NUMA_NO_NODE,
> > > > > -					 __builtin_return_address(0));
> > > > > -	}
> > > > > +	module_init_limits();
> > > > 
> > > > Hmm, this used to be run from subsys_initcall(), but now you're running
> > > > it _really_ early, before random_init(), so randomization of the module
> > > > space is no longer going to be very random if we don't have early entropy
> > > > from the firmware or the CPU, which is likely to be the case on most SoCs.
> > > 
> > > Well, it will be as random as KASLR. Won't that be enough?
> > 
> > I don't think that's true -- we have the 'kaslr-seed' property for KASLR,
> > but I'm not seeing anything like that for the module randomisation and I
> > also don't see why we need to set these limits so early.
> 
> x86 needs execmem initialized before ftrace_init() so I thought it would be
> best to setup execmem along with most of MM in mm_core_init().
> 
> I'll move execmem initialization for !x86 to a later point, say
> core_initcall.

Thanks, Mike.

Will