linux-kernel - Re: [PATCH RFC] kprobes: Remove MODULES dependency

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Message-ID: <20200713054955.GC956284@linux.intel.com>
Date:   Mon, 13 Jul 2020 08:49:55 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>, Alexandre Ghiti <alex@...ti.fr>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jiri Olsa <jolsa@...hat.com>, hch@....de
Subject: Re: [PATCH RFC] kprobes: Remove MODULES dependency

On Fri, Jul 10, 2020 at 01:32:38PM +0200, Peter Zijlstra wrote:
> On Fri, Jul 10, 2020 at 07:32:57PM +0900, Masami Hiramatsu wrote:
> > > -	page = module_alloc(PAGE_SIZE);
> > > +	page = vmalloc(PAGE_SIZE);
> > 
> > No, you can not use vmalloc here. The reason why we use module_alloc()
> > is to allocate the executable memory for trampoline code.
> > So, you need to use vmalloc_exec() instead.
> 
> vmalloc_exec() would be broken too, also hch recently got rid of that
> thing.
> 
> module_alloc() really is the only sane choice here.
> 
> We should make module_alloc() unconditionally available, and maybe even
> rename it to text_alloc().

Thanks for the remarks.

The current module_alloc looks like this:

void * __weak module_alloc(unsigned long size)
{
	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
			GFP_KERNEL, PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS,
			NUMA_NO_NODE, __builtin_return_address(0));
}

What if I create inline functions for text_alloc() and text_memfree() and
convert this function as:

void * __weak module_alloc(unsigned long size)
{
	return text_alloc(size);
}

/Jarkko