From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
David Laight <David.Laight@aculab.com>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [RFC PATCH 1/3] static_call: Add static call infrastructure
Date: Fri, 9 Nov 2018 18:33:03 +0100 [thread overview]
Message-ID: <CAKv+Gu-9XYOwAPJ5m6F4Cn9Uo6dvbtEG9p0knX+_XcjHp2QKGA@mail.gmail.com> (raw)
In-Reply-To: <20181109173106.kbghzsdsu7oachl6@treble>
On 9 November 2018 at 18:31, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Fri, Nov 09, 2018 at 06:25:24PM +0100, Ard Biesheuvel wrote:
>> On 9 November 2018 at 16:14, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>> > On 9 November 2018 at 16:10, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>> >> On Fri, Nov 09, 2018 at 02:39:17PM +0100, Ard Biesheuvel wrote:
>> >>> > + for (site = start; site < stop; site++) {
>> >>> > + struct static_call_key *key = static_call_key(site);
>> >>> > + unsigned long addr = static_call_addr(site);
>> >>> > +
>> >>> > + if (list_empty(&key->site_mods)) {
>> >>> > + struct static_call_mod *mod;
>> >>> > +
>> >>> > + mod = kzalloc(sizeof(*mod), GFP_KERNEL);
>> >>> > + if (!mod) {
>> >>> > + WARN(1, "Failed to allocate memory for static calls");
>> >>> > + return;
>> >>> > + }
>> >>> > +
>> >>> > + mod->sites = site;
>> >>> > + list_add_tail(&mod->list, &key->site_mods);
>> >>> > +
>> >>> > + /*
>> >>> > + * The trampoline should no longer be used. Poison it
>> >>> > + * it with a BUG() to catch any stray callers.
>> >>> > + */
>> >>> > + arch_static_call_poison_tramp(addr);
>> >>>
>> >>> This patches the wrong thing: the trampoline is at key->func not addr.
>> >>
>> >> If you look at the x86 implementation, it actually does poison the
>> >> trampoline.
>> >>
>> >> The address of the trampoline isn't actually known here. key->func
>> >> isn't the trampoline address; it's the destination func address.
>> >>
>> >> So instead I passed the address of the call instruction. The arch code
>> >> then reads the instruction to find the callee (the trampoline).
>> >>
>> >> The code is a bit confusing. To make it more obvious, maybe we should
>> >> add another arch function to read the call destination. Then this code
>> >> can pass that into arch_static_call_poison_tramp().
>> >>
>> >
>> > Ah right, so I am basically missing a dereference in my
>> > arch_static_call_poison_tramp() code if this breaks.
>> >
>>
>> Could we call it 'defuse' rather than 'poision'? On arm64, we will
>> need to keep it around to bounce function calls that are out of range,
>> and replace it with a PLT sequence.
>
> Ok, but doesn't that defeat the purpose of the inline approach?
>
It does. But this only occurs when a module is loaded far away, and
this will only happen if you have 2 GB range KASLR enabled, or your
128 MB module region gets exhausted for some reason, so the majority
of calls should use a single relative branch.
next prev parent reply other threads:[~2018-11-09 17:33 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-08 21:15 [PATCH RFC 0/3] Static calls Josh Poimboeuf
2018-11-08 21:15 ` [RFC PATCH 1/3] static_call: Add static call infrastructure Josh Poimboeuf
2018-11-09 9:51 ` Ard Biesheuvel
2018-11-09 14:55 ` Josh Poimboeuf
2018-11-09 13:39 ` Ard Biesheuvel
2018-11-09 15:10 ` Josh Poimboeuf
2018-11-09 15:14 ` Ard Biesheuvel
2018-11-09 17:25 ` Ard Biesheuvel
2018-11-09 17:31 ` Josh Poimboeuf
2018-11-09 17:33 ` Ard Biesheuvel [this message]
2018-11-09 17:46 ` Josh Poimboeuf
2018-11-09 17:52 ` Ard Biesheuvel
2018-11-09 17:53 ` Ard Biesheuvel
2018-11-09 19:03 ` Josh Poimboeuf
2018-11-09 19:12 ` Ard Biesheuvel
2018-11-09 17:33 ` Josh Poimboeuf
2018-11-09 18:33 ` Steven Rostedt
2018-11-09 19:35 ` Josh Poimboeuf
2018-11-09 19:57 ` Steven Rostedt
2018-11-09 20:34 ` Josh Poimboeuf
2018-11-10 5:10 ` Steven Rostedt
2018-11-10 11:58 ` Ard Biesheuvel
2018-11-10 13:09 ` Steven Rostedt
2018-11-12 3:07 ` Josh Poimboeuf
2018-11-12 4:39 ` Ard Biesheuvel
2018-11-12 4:56 ` Josh Poimboeuf
2018-11-12 5:02 ` Ard Biesheuvel
2018-11-10 11:56 ` Ard Biesheuvel
2018-11-08 21:15 ` [RFC PATCH 2/3] x86/static_call: Add x86 unoptimized static call implementation Josh Poimboeuf
2018-11-08 21:15 ` [RFC PATCH 3/3] x86/static_call: Add optimized static call implementation for 64-bit Josh Poimboeuf
2018-11-08 21:24 ` [PATCH RFC 0/3] Static calls Josh Poimboeuf
2018-11-09 7:28 ` Ingo Molnar
2018-11-09 7:50 ` Ingo Molnar
2018-11-09 13:50 ` Ard Biesheuvel
2018-11-09 15:20 ` Josh Poimboeuf
2018-11-10 23:20 ` Peter Zijlstra
2018-11-11 13:42 ` Ard Biesheuvel
2018-11-11 14:25 ` Peter Zijlstra
2018-11-09 14:45 ` Josh Poimboeuf
2018-11-12 5:02 ` Ingo Molnar
2018-11-12 5:30 ` Josh Poimboeuf
2018-11-12 9:39 ` Ard Biesheuvel
2018-11-12 22:52 ` Josh Poimboeuf
2018-11-12 17:03 ` Steven Rostedt
2018-11-12 22:56 ` Josh Poimboeuf
2018-11-12 5:34 ` Andy Lutomirski
2018-11-09 15:16 ` Andy Lutomirski
2018-11-09 15:21 ` Josh Poimboeuf
2018-11-09 16:41 ` Josh Poimboeuf
2018-11-09 18:42 ` Steven Rostedt
2018-11-09 19:05 ` Andy Lutomirski
2018-11-09 19:37 ` Steven Rostedt
2018-11-09 19:44 ` Josh Poimboeuf
2018-11-09 19:59 ` Steven Rostedt
2018-11-09 20:36 ` Josh Poimboeuf
2018-11-10 15:13 ` Masami Hiramatsu
2018-11-09 20:53 ` Rasmus Villemoes
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