linux-kernel - Re: [PATCH v3 1/3] kprobes: Add text_alloc() and text

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Date:   Wed, 15 Jul 2020 12:38:19 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        Jessica Yu <jeyu@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Alexandre Ghiti <alex@...ti.fr>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Stephen Boyd <sboyd@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Babu Moger <Babu.Moger@....com>,
        Omar Sandoval <osandov@...com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Marco Elver <elver@...gle.com>,
        Brian Gerst <brgerst@...il.com>, Jiri Kosina <jkosina@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCH v3 1/3] kprobes: Add text_alloc() and text_free()

On Wed, Jul 15, 2020 at 05:27:32PM +0900, Masami Hiramatsu wrote:
> 
> On Wed, 15 Jul 2020 01:32:27 +0300
> Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com> wrote:
> > [...]
> > -void *module_alloc(unsigned long size)
> > -{
> > -	void *p;
> > -
> > -	if (PAGE_ALIGN(size) > MODULES_LEN)
> > -		return NULL;
> > -
> > -	p = __vmalloc_node_range(size, MODULE_ALIGN,
> > -				    MODULES_VADDR + get_module_load_offset(),
> > -				    MODULES_END, GFP_KERNEL,
> > -				    PAGE_KERNEL, 0, NUMA_NO_NODE,
> > -				    __builtin_return_address(0));
> > -	if (p && (kasan_module_alloc(p, size) < 0)) {
> > -		vfree(p);
> > -		return NULL;
> > -	}
> > -
> > -	return p;
> > -}
> 
> Please don't touch this module_alloc() at all. Then we can
> just call __vmalloc_node_range() in the text_alloc().

Hm? I thought the requirement was that trampolines needed to stay within
a certain distance of kernel text and that the module_alloc() enforced
that?

-- 
Kees Cook