linux-kernel - Re: [PATCH v2 4/7] arm64/modules: Add rlimit checking for arm64 modules

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Message-ID: <a89e6d7bbcfba2ebaad927fac0da131ded59aa28.camel@intel.com>
Date:   Fri, 12 Oct 2018 22:01:45 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "jeyu@...nel.org" <jeyu@...nel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
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Subject: Re: [PATCH v2 4/7] arm64/modules: Add rlimit checking for arm64
 modules

On Fri, 2018-10-12 at 16:32 +0200, Jessica Yu wrote:
> +++ Dave Hansen [11/10/18 16:47 -0700]:
> > On 10/11/2018 04:31 PM, Rick Edgecombe wrote:
> > > +	if (check_inc_mod_rlimit(size))
> > > +		return NULL;
> > > +
> > >  	p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
> > >  				module_alloc_base + MODULES_VSIZE,
> > >  				gfp_mask, PAGE_KERNEL_EXEC, 0,
> > > @@ -65,6 +68,8 @@ void *module_alloc(unsigned long size)
> > >  		return NULL;
> > >  	}
> > > 
> > > +	update_mod_rlimit(p, size);
> > 
> > Is there a reason we couldn't just rename all of the existing per-arch
> > module_alloc() calls to be called, say, "arch_module_alloc()", then put
> > this new rlimit code in a generic helper that does:
> > 
> > 
> > 	if (check_inc_mod_rlimit(size))
> > 		return NULL;
> > 
> > 	p = arch_module_alloc(...);
> > 
> > 	...
> > 
> > 	update_mod_rlimit(p, size);
> > 
> 
> I second this suggestion. Just make module_{alloc,memfree} generic,
> non-weak functions that call the rlimit helpers in addition to the
> arch-specific arch_module_{alloc,memfree} functions.
> 
> Jessica

Ok, thanks. I am going to try another version of this with just a system wide
BPF JIT limit based on the problems Jann brought up. I think it would be nice to
have a module space limit, but as far as I know the only way today un-privlidged 
users could fill the space is from BPF JIT. Unless you see another purpose long
term?

Rick