From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>,
Sami Tolvanen <samitolvanen@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Andrew Cooper <Andrew.Cooper3@citrix.com>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Johannes Wikner <kwikner@ethz.ch>,
Alyssa Milburn <alyssa.milburn@linux.intel.com>,
Jann Horn <jannh@google.com>, "H.J. Lu" <hjl.tools@gmail.com>,
Joao Moreira <joao.moreira@intel.com>,
Joseph Nuzman <joseph.nuzman@intel.com>,
Steven Rostedt <rostedt@goodmis.org>,
Juergen Gross <jgross@suse.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [patch 00/38] x86/retbleed: Call depth tracking mitigation
Date: Wed, 20 Jul 2022 11:00:44 +0200 [thread overview]
Message-ID: <87y1wotayr.ffs@tglx> (raw)
In-Reply-To: <YtXx8r5zfqZ12M04@worktop.programming.kicks-ass.net>
On Tue, Jul 19 2022 at 01:51, Peter Zijlstra wrote:
> On Mon, Jul 18, 2022 at 03:48:04PM -0700, Sami Tolvanen wrote:
>> On Mon, Jul 18, 2022 at 2:18 PM Peter Zijlstra <peterz@infradead.org> wrote:
>> > Ofc, we can still put the whole:
>> >
>> > sarq $5, PER_CPU_VAR(__x86_call_depth);
>> > jmp \func_direct
>> >
>> > thing in front of that.
>>
>> Sure, that would work.
>
> So if we assume \func starts with ENDBR, and further assume we've fixed
> up every direct jmp/call to land at +4, we can overwrite the ENDBR with
> part of the SARQ, that leaves us 6 more byte, placing the immediate at
> -10 if I'm not mis-counting.
>
> Now, the call sites are:
>
> 41 81 7b fa 78 56 34 12 cmpl $0x12345678, -6(%r11)
> 74 02 je 1f
> 0f 0b ud2
> e8 00 00 00 00 1: call __x86_indirect_thunk_r11
>
> That means the offset of +10 lands in the middle of the CALL
> instruction, and since we only have 16 thunks there is a limited number
> of byte patterns available there.
>
> This really isn't as nice as the -6 but might just work well enough,
> hmm?
So I added a 32byte padding and put the thunk at the start:
sarq $5, PER_CPU_VAR(__x86_call_depth);
jmp \func_direct
For sockperf that costs about 1% performance vs. the 16 byte
variant. For mitigations=off it's a ~0.5% drop.
That's on a SKL. Did not check on other systems yet.
Thanks,
tglx
next prev parent reply other threads:[~2022-07-20 9:00 UTC|newest]
Thread overview: 142+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-16 23:17 [patch 00/38] x86/retbleed: Call depth tracking mitigation Thomas Gleixner
2022-07-16 23:17 ` [patch 01/38] x86/paravirt: Ensure proper alignment Thomas Gleixner
2022-07-16 23:17 ` [patch 02/38] x86/cpu: Use native_wrmsrl() in load_percpu_segment() Thomas Gleixner
2022-07-17 0:22 ` Andrew Cooper
2022-07-17 15:20 ` Linus Torvalds
2022-07-17 19:08 ` Thomas Gleixner
2022-07-17 20:08 ` Thomas Gleixner
2022-07-17 20:13 ` Thomas Gleixner
2022-07-17 21:54 ` Thomas Gleixner
2022-07-18 5:11 ` Juergen Gross
2022-07-18 6:54 ` Thomas Gleixner
2022-07-18 8:55 ` Thomas Gleixner
2022-07-18 9:31 ` Peter Zijlstra
2022-07-18 10:33 ` Thomas Gleixner
2022-07-18 11:42 ` Thomas Gleixner
2022-07-18 17:52 ` [patch 0/3] x86/cpu: Sanitize switch_to_new_gdt() Thomas Gleixner
2022-07-18 17:52 ` [patch 1/3] x86/cpu: Remove segment load from switch_to_new_gdt() Thomas Gleixner
2022-07-18 18:43 ` Linus Torvalds
2022-07-18 18:55 ` Thomas Gleixner
2022-07-18 17:52 ` [patch 2/3] x86/cpu: Get rid of redundant switch_to_new_gdt() invocations Thomas Gleixner
2022-07-18 17:52 ` [patch 3/3] x86/cpu: Re-enable stackprotector Thomas Gleixner
2022-07-16 23:17 ` [patch 03/38] x86/modules: Set VM_FLUSH_RESET_PERMS in module_alloc() Thomas Gleixner
2022-07-16 23:17 ` [patch 04/38] x86/vdso: Ensure all kernel code is seen by objtool Thomas Gleixner
2022-07-16 23:17 ` [patch 05/38] btree: Initialize early when builtin Thomas Gleixner
2022-07-16 23:17 ` [patch 06/38] objtool: Allow GS relative relocs Thomas Gleixner
2022-07-16 23:17 ` [patch 07/38] objtool: Track init section Thomas Gleixner
2022-07-16 23:17 ` [patch 08/38] objtool: Add .call_sites section Thomas Gleixner
2022-07-16 23:17 ` [patch 09/38] objtool: Add .sym_sites section Thomas Gleixner
2022-07-16 23:17 ` [patch 10/38] objtool: Add --hacks=skylake Thomas Gleixner
2022-07-16 23:17 ` [patch 11/38] objtool: Allow STT_NOTYPE -> STT_FUNC+0 tail-calls Thomas Gleixner
2022-07-16 23:17 ` [patch 12/38] x86/entry: Make sync_regs() invocation a tail call Thomas Gleixner
2022-07-16 23:17 ` [patch 13/38] x86/modules: Make module_alloc() generally available Thomas Gleixner
2022-07-16 23:17 ` [patch 14/38] x86/Kconfig: Add CONFIG_CALL_THUNKS Thomas Gleixner
2022-07-16 23:17 ` [patch 15/38] x86/retbleed: Add X86_FEATURE_CALL_DEPTH Thomas Gleixner
2022-07-16 23:17 ` [patch 16/38] modules: Make struct module_layout unconditionally available Thomas Gleixner
2022-07-16 23:17 ` [patch 17/38] module: Add arch_data to module_layout Thomas Gleixner
2022-07-16 23:17 ` [patch 18/38] mm/vmalloc: Provide huge page mappings Thomas Gleixner
2022-07-16 23:17 ` [patch 19/38] x86/module: Provide __module_alloc() Thomas Gleixner
2022-07-16 23:17 ` [patch 20/38] x86/alternatives: Provide text_poke_[copy|set]_locked() Thomas Gleixner
2022-07-16 23:17 ` [patch 21/38] x86/entry: Make some entry symbols global Thomas Gleixner
2022-07-16 23:17 ` [patch 22/38] x86/paravirt: Make struct paravirt_call_site unconditionally available Thomas Gleixner
2022-07-16 23:17 ` [patch 23/38] x86/callthunks: Add call patching for call depth tracking Thomas Gleixner
2022-07-16 23:17 ` [patch 24/38] module: Add layout for callthunks tracking Thomas Gleixner
2022-07-16 23:17 ` [patch 25/38] x86/modules: Add call thunk patching Thomas Gleixner
2022-07-16 23:17 ` [patch 26/38] x86/returnthunk: Allow different return thunks Thomas Gleixner
2022-07-16 23:17 ` [patch 27/38] x86/asm: Provide ALTERNATIVE_3 Thomas Gleixner
2022-07-16 23:17 ` [patch 28/38] x86/retbleed: Add SKL return thunk Thomas Gleixner
2022-07-16 23:17 ` [patch 29/38] x86/retpoline: Add SKL retthunk retpolines Thomas Gleixner
2022-07-16 23:17 ` [patch 30/38] x86/retbleed: Add SKL call thunk Thomas Gleixner
2022-07-16 23:18 ` [patch 31/38] x86/calldepth: Add ret/call counting for debug Thomas Gleixner
2022-07-16 23:18 ` [patch 32/38] static_call: Add call depth tracking support Thomas Gleixner
2022-07-16 23:18 ` [patch 33/38] kallsyms: Take callthunks into account Thomas Gleixner
2022-07-16 23:18 ` [patch 34/38] x86/orc: Make it callthunk aware Thomas Gleixner
2022-07-16 23:18 ` [patch 35/38] kprobes: Add callthunk blacklisting Thomas Gleixner
2022-07-16 23:18 ` [patch 36/38] x86/ftrace: Make it call depth tracking aware Thomas Gleixner
2022-07-18 21:01 ` Steven Rostedt
2022-07-19 8:46 ` Peter Zijlstra
2022-07-19 13:06 ` Steven Rostedt
2022-07-16 23:18 ` [patch 37/38] x86/bpf: Emit call depth accounting if required Thomas Gleixner
2022-07-19 5:30 ` Alexei Starovoitov
2022-07-19 8:34 ` Peter Zijlstra
2022-07-16 23:18 ` [patch 38/38] x86/retbleed: Add call depth tracking mitigation Thomas Gleixner
2022-07-17 9:45 ` [patch 00/38] x86/retbleed: Call " David Laight
2022-07-17 15:07 ` Thomas Gleixner
2022-07-17 17:56 ` David Laight
2022-07-17 19:15 ` Thomas Gleixner
2022-07-18 19:29 ` Thomas Gleixner
2022-07-18 19:30 ` Thomas Gleixner
2022-07-18 19:51 ` Linus Torvalds
2022-07-18 20:44 ` Thomas Gleixner
2022-07-18 21:01 ` Linus Torvalds
2022-07-18 21:43 ` Peter Zijlstra
2022-07-18 22:34 ` Linus Torvalds
2022-07-18 23:52 ` Peter Zijlstra
2022-07-18 21:18 ` Peter Zijlstra
2022-07-18 22:22 ` Thomas Gleixner
2022-07-18 22:47 ` Joao Moreira
2022-07-18 22:55 ` Sami Tolvanen
2022-07-18 23:08 ` Joao Moreira
2022-07-18 23:19 ` Thomas Gleixner
2022-07-18 23:42 ` Linus Torvalds
2022-07-18 23:52 ` Linus Torvalds
2022-07-18 23:57 ` Peter Zijlstra
2022-07-19 0:03 ` Linus Torvalds
2022-07-19 0:11 ` Linus Torvalds
2022-07-19 0:23 ` Peter Zijlstra
2022-07-19 1:02 ` Linus Torvalds
2022-07-19 17:19 ` Sami Tolvanen
2022-07-20 21:13 ` Peter Zijlstra
2022-07-21 8:21 ` David Laight
2022-07-21 10:56 ` David Laight
2022-07-21 15:54 ` Peter Zijlstra
2022-07-21 17:55 ` Peter Zijlstra
2022-07-21 18:06 ` Linus Torvalds
2022-07-21 18:27 ` Peter Zijlstra
2022-07-21 18:32 ` Linus Torvalds
2022-07-21 20:22 ` Joao Moreira
2022-07-22 0:16 ` Sami Tolvanen
2022-07-22 10:23 ` Peter Zijlstra
2022-07-22 15:38 ` Sami Tolvanen
2022-07-21 22:01 ` David Laight
2022-07-22 11:03 ` Peter Zijlstra
2022-07-22 13:27 ` David Laight
2022-07-23 9:50 ` Thomas Gleixner
2022-07-19 0:01 ` Linus Torvalds
2022-07-19 0:19 ` Joao Moreira
2022-07-19 17:21 ` Sami Tolvanen
2022-07-19 17:58 ` Joao Moreira
2022-07-19 8:26 ` David Laight
2022-07-19 16:27 ` Linus Torvalds
2022-07-19 17:23 ` Sami Tolvanen
2022-07-19 17:27 ` Linus Torvalds
2022-07-19 18:06 ` Sami Tolvanen
2022-07-19 20:10 ` Peter Zijlstra
2022-07-18 22:48 ` Sami Tolvanen
2022-07-18 22:59 ` Thomas Gleixner
2022-07-18 23:10 ` Sami Tolvanen
2022-07-18 23:39 ` Linus Torvalds
2022-07-18 23:51 ` Peter Zijlstra
2022-07-20 9:00 ` Thomas Gleixner [this message]
2022-07-20 16:55 ` Sami Tolvanen
2022-07-20 19:42 ` Sami Tolvanen
2022-07-22 20:11 ` Tim Chen
2022-07-22 22:18 ` Linus Torvalds
2022-07-18 19:55 ` Thomas Gleixner
2022-07-19 10:24 ` Virt " Andrew Cooper
2022-07-19 14:13 ` Thomas Gleixner
2022-07-19 16:23 ` Andrew Cooper
2022-07-19 21:17 ` Thomas Gleixner
2022-07-19 14:45 ` Michael Kelley (LINUX)
2022-07-19 20:16 ` Peter Zijlstra
2022-07-20 16:57 ` [patch 00/38] x86/retbleed: " Steven Rostedt
2022-07-20 17:09 ` Linus Torvalds
2022-07-20 17:24 ` Peter Zijlstra
2022-07-20 17:50 ` Steven Rostedt
2022-07-20 18:07 ` Linus Torvalds
2022-07-20 18:31 ` Steven Rostedt
2022-07-20 18:43 ` Linus Torvalds
2022-07-20 19:11 ` Steven Rostedt
2022-07-20 19:36 ` Kees Cook
2022-07-20 19:43 ` Steven Rostedt
2022-07-20 21:36 ` Peter Zijlstra
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