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

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Message-ID: <20231026102438.GA6924@willie-the-truck>
Date:   Thu, 26 Oct 2023 11:24:39 +0100
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 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
> > > @@ -20,6 +20,7 @@
> > >  #include <linux/random.h>
> > >  #include <linux/scs.h>
> > >  #include <linux/vmalloc.h>
> > > +#include <linux/execmem.h>
> > >  
> > >  #include <asm/alternative.h>
> > >  #include <asm/insn.h>
> > > @@ -108,46 +109,38 @@ static int __init module_init_limits(void)
> > >  
> > >  	return 0;
> > >  }
> > > -subsys_initcall(module_init_limits);
> > >  
> > > -void *module_alloc(unsigned long size)
> > > +static struct execmem_params execmem_params __ro_after_init = {
> > > +	.ranges = {
> > > +		[EXECMEM_DEFAULT] = {
> > > +			.flags = EXECMEM_KASAN_SHADOW,
> > > +			.alignment = MODULE_ALIGN,
> > > +		},
> > > +	},
> > > +};
> > > +
> > > +struct execmem_params __init *execmem_arch_params(void)
> > >  {
> > > -	void *p = NULL;
> > > +	struct execmem_range *r = &execmem_params.ranges[EXECMEM_DEFAULT];
> > >  
> > > -	/*
> > > -	 * Where possible, prefer to allocate within direct branch range of the
> > > -	 * kernel such that no PLTs are necessary.
> > > -	 */
> > 
> > Why are you removing this comment? I think you could just move it next
> > to the part where we set a 128MiB range.
>  
> Oops, my bad. Will add it back.

Thanks.

> > > -	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.

Will