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From: Nadav Amit <namit@vmware.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	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>, Julia Cartwright <julia@ni.com>,
	Jessica Yu <jeyu@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Edward Cree <ecree@solarflare.com>,
	Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [PATCH v3 0/6] Static calls
Date: Fri, 11 Jan 2019 15:48:59 +0000
Message-ID: <F6735FF5-4D62-4C4E-A145-751E6469CE9E@vmware.com> (raw)
In-Reply-To: <20190111151525.tf7lhuycyyvjjxez@treble>

> On Jan 11, 2019, at 7:15 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> 
> On Fri, Jan 11, 2019 at 01:47:01AM +0000, Nadav Amit wrote:
>> Here is an alternative idea (although similar to Steven’s and my code).
>> 
>> Assume that we always clobber R10, R11 on static-calls explicitly, as anyhow
>> should be done by the calling convention (and gcc plugin should allow us to
>> enforce). Also assume that we hold a table with all source RIP and the
>> matching target.
>> 
>> Now, in the int3 handler can you take the faulting RIP and search for it in
>> the “static-calls” table, writing the RIP+5 (offset) into R10 (return
>> address) and the target into R11. You make the int3 handler to divert the
>> code execution by changing pt_regs->rip to point to a new function that does:
>> 
>> 	push R10
>> 	jmp __x86_indirect_thunk_r11
>> 
>> And then you are done. No?
> 
> IIUC, that sounds pretty much like what Steven proposed:
> 
>  https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20181129122000.7fb4fb04%40gandalf.local.home&amp;data=02%7C01%7Cnamit%40vmware.com%7Ce3f0b96a1e83417af48808d677d7a147%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636828165370908292&amp;sdata=PFzrJQzoa21IRYmEuqHSSGYrNZt0zIo8TGOZa3NWbOE%3D&amp;reserved=0

Stupid me. I’ve remembered it slightly different (the caller saving the
target in a register).

> I liked the idea, BUT, how would it work for callee-saved PV ops?  In
> that case there's only one clobbered register to work with (rax).

That’s would be more tricky. How about using a per-CPU trampoline code to
hold a direct call to the target and temporarily disable preemption (which
might be simpler by disabling IRQs):

Static-call modifier:

        1. synchronize_sched() to ensure per-cpu trampoline is not used
	2. Patches the jmp in a per-cpu trampoline (see below)
	3. Saves the call source RIP in [per-cpu scratchpad RIP] (below) 
	4. Configures the int3 handler to use static-call int3 handler
	5. Patches the call target (as it currently does).

Static-call int3 handler:
	1. Changes flags on the stack to keep IRQs disabled on return
	2. Jumps to per-cpu trampoline on return

Per-cpu trampoline:
	push [per-CPU scratchpad RIP]
	sti
	jmp [ target ] (this one is patched)

Note that no IRQ should be possible between the STI and the JMP due to STI
blocking.

What do you say?


  reply index

Thread overview: 90+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-09 22:59 Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 1/6] compiler.h: Make __ADDRESSABLE() symbol truly unique Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 2/6] static_call: Add basic static call infrastructure Josh Poimboeuf
2019-01-10 14:03   ` Edward Cree
2019-01-10 18:37     ` Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 3/6] x86/static_call: Add out-of-line static call implementation Josh Poimboeuf
2019-01-10  0:16   ` Nadav Amit
2019-01-10 16:28     ` Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 4/6] static_call: Add inline static call infrastructure Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 5/6] x86/alternative: Use a single access in text_poke() where possible Josh Poimboeuf
2019-01-10  9:32   ` Nadav Amit
2019-01-10 17:20     ` Josh Poimboeuf
2019-01-10 17:29       ` Nadav Amit
2019-01-10 17:32       ` Steven Rostedt
2019-01-10 17:42         ` Sean Christopherson
2019-01-10 17:57           ` Steven Rostedt
2019-01-10 18:04             ` Sean Christopherson
2019-01-10 18:21               ` Josh Poimboeuf
2019-01-10 18:24               ` Steven Rostedt
2019-01-11 12:10               ` Alexandre Chartre
2019-01-11 15:28                 ` Josh Poimboeuf
2019-01-11 16:46                   ` Alexandre Chartre
2019-01-11 16:57                     ` Josh Poimboeuf
2019-01-11 17:41                       ` Jason Baron
2019-01-11 17:54                         ` Nadav Amit
2019-01-15 11:10                       ` Alexandre Chartre
2019-01-15 16:19                         ` Steven Rostedt
2019-01-15 16:45                           ` Alexandre Chartre
2019-01-11  0:59           ` hpa
2019-01-11  1:34             ` Sean Christopherson
2019-01-11  8:13               ` hpa
2019-01-09 22:59 ` [PATCH v3 6/6] x86/static_call: Add inline static call implementation for x86-64 Josh Poimboeuf
2019-01-10  1:21 ` [PATCH v3 0/6] Static calls Nadav Amit
2019-01-10 16:44   ` Josh Poimboeuf
2019-01-10 17:32     ` Nadav Amit
2019-01-10 18:18       ` Josh Poimboeuf
2019-01-10 19:45         ` Nadav Amit
2019-01-10 20:32           ` Josh Poimboeuf
2019-01-10 20:48             ` Nadav Amit
2019-01-10 20:57               ` Josh Poimboeuf
2019-01-10 21:47                 ` Nadav Amit
2019-01-10 17:31 ` Linus Torvalds
2019-01-10 20:51   ` H. Peter Anvin
2019-01-10 20:30 ` Peter Zijlstra
2019-01-10 20:52   ` Josh Poimboeuf
2019-01-10 23:02     ` Linus Torvalds
2019-01-11  0:56       ` Andy Lutomirski
2019-01-11  1:47         ` Nadav Amit
2019-01-11 15:15           ` Josh Poimboeuf
2019-01-11 15:48             ` Nadav Amit [this message]
2019-01-11 16:07               ` Josh Poimboeuf
2019-01-11 17:23                 ` Nadav Amit
2019-01-11 19:03             ` Linus Torvalds
2019-01-11 19:17               ` Nadav Amit
2019-01-11 19:23               ` hpa
2019-01-11 19:33                 ` Nadav Amit
2019-01-11 19:34                 ` Linus Torvalds
2019-01-13  0:34                   ` hpa
2019-01-13  0:36                   ` hpa
2019-01-11 19:39                 ` Jiri Kosina
2019-01-14  2:31                   ` H. Peter Anvin
2019-01-14  2:40                     ` H. Peter Anvin
2019-01-14 20:11                       ` Andy Lutomirski
2019-01-14 22:00                       ` H. Peter Anvin
2019-01-14 22:54                         ` H. Peter Anvin
2019-01-15  3:05                           ` Andy Lutomirski
2019-01-15  5:01                             ` H. Peter Anvin
2019-01-15  5:37                               ` H. Peter Anvin
2019-01-14 23:27                         ` Andy Lutomirski
2019-01-14 23:51                           ` Nadav Amit
2019-01-15  2:28                           ` hpa
2019-01-11 20:04               ` Josh Poimboeuf
2019-01-11 20:12                 ` Linus Torvalds
2019-01-11 20:31                   ` Josh Poimboeuf
2019-01-11 20:46                     ` Linus Torvalds
2019-01-11 21:05                       ` Andy Lutomirski
2019-01-11 21:10                         ` Linus Torvalds
2019-01-11 21:32                           ` Josh Poimboeuf
2019-01-14 12:28                         ` Peter Zijlstra
2019-01-11 21:22                       ` Josh Poimboeuf
2019-01-11 21:23                         ` Josh Poimboeuf
2019-01-11 21:25                         ` Josh Poimboeuf
2019-01-11 21:36                         ` Nadav Amit
2019-01-11 21:41                           ` Josh Poimboeuf
2019-01-11 21:55                             ` Steven Rostedt
2019-01-11 21:59                               ` Nadav Amit
2019-01-11 21:56                             ` Nadav Amit
2019-01-12 23:54                         ` Andy Lutomirski
2020-02-17 21:10     ` Jann Horn
2020-02-17 21:57       ` Steven Rostedt

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