Re: [PATCH v3 04/13] mm/execmem, arch: convert remaining overrides of module_alloc to execmem

[Will Deacon]

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