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From: Tim Chen <tim.c.chen@linux.intel.com>
To: Kevin Easton <kevin@guarana.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	linux-kernel@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andi Kleen <ak@linux.intel.com>,
	Arjan Van De Ven <arjan.van.de.ven@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Asit Mallick <asit.k.mallick@intel.com>,
	Jason Baron <jbaron@akamai.com>
Subject: Re: [PATCH 30/35] x86/speculation: Use Indirect Branch Prediction Barrier in context switch
Date: Fri, 19 Jan 2018 12:26:46 -0800	[thread overview]
Message-ID: <510876ab-97cd-9ec9-cc5e-0a2db038704b@linux.intel.com> (raw)
In-Reply-To: <20180119040329.GA21544@la.guarana.org>

On 01/18/2018 08:03 PM, Kevin Easton wrote:
> On Thu, Jan 18, 2018 at 04:38:32PM -0800, Tim Chen wrote:
>> On 01/18/2018 05:48 AM, Peter Zijlstra wrote:
>>>
>>> +		/*
>>> +		 * Avoid user/user BTB poisoning by flushing the branch predictor
>>> +		 * when switching between processes. This stops one process from
>>> +		 * doing spectre-v2 attacks on another process's data.
>>> +		 */
>>> +		indirect_branch_prediction_barrier();
>>> +
>>
>> Some optimizations can be done here to avoid overhead in barrier call.
>>
>> For example, don't do the barrier if prev and next mm are
>> the same.  If the two process trust each other, or the new process
>> already have rights to look into the previous process,
>> the barrier could be skipped.
> 
> Isn't it the other way around with the BTB poisoning? previous is
> potentially attacking next, so the barrier can be avoided only if previous
> is allowed to ptrace next?
> 

Yes, if the next process don't trust the previous process, then
doing a prediction barrier before the context switch makes sense.

Tim

  reply	other threads:[~2018-01-19 20:26 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-18 13:48 [PATCH 00/35] jump_label, objtool, IBRS and IBPB Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 01/35] jump_label: Add branch hints to static_branch_{un,}likely() Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 02/35] sched: Optimize ttwu_stat() Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 03/35] x86: Reindent _static_cpu_has Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 04/35] x86: Update _static_cpu_has to use all named variables Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 05/35] x86: Add a type field to alt_instr Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 06/35] objtool: Implement base jump_assert support Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 07/35] x86: Annotate static_cpu_has alternative Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 08/35] objtool: Implement jump_assert for _static_cpu_has() Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 09/35] objtool: Introduce special_type Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 10/35] x86/jump_label: Implement arch_static_assert() Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 11/35] objtool: Add retpoline validation Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 12/35] x86/paravirt: Annotate indirect calls Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 13/35] x86,nospec: Annotate indirect calls/jumps Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 14/35] x86: Annotate indirect jump in head_64.S Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 15/35] objtool: More complex static jump implementation Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 16/35] objtool: Use existing global variables for options Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 17/35] objtool: Even more complex static block checks Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 18/35] objtool: Another static block fail Peter Zijlstra, Peter Zijlstra
2018-01-19 16:42   ` Peter Zijlstra
2018-01-29 18:01     ` Josh Poimboeuf
2018-01-29 18:24       ` Peter Zijlstra
2018-01-18 13:48 ` [PATCH 19/35] objtool: Skip static assert when KCOV/KASAN Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 20/35] x86: Force asm-goto Peter Zijlstra, Peter Zijlstra
2018-01-18 16:25   ` David Woodhouse
2018-01-18 13:48 ` [PATCH 21/35] x86: Remove FAST_FEATURE_TESTS Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 22/35] x86/cpufeatures: Detect Speculation control feature Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 23/35] x86/speculation: Add basic speculation control code Peter Zijlstra, Peter Zijlstra
2018-01-18 16:37   ` Josh Poimboeuf
2018-01-18 17:08     ` Dave Hansen
2018-01-18 17:12       ` Paolo Bonzini
2018-01-18 18:24         ` Josh Poimboeuf
2018-01-18 19:08           ` Andrea Arcangeli
2018-01-18 23:25             ` Andy Lutomirski
2018-01-18 23:35               ` Andrew Cooper
2018-01-19  1:41               ` Andrea Arcangeli
2018-01-19  4:10                 ` Andy Lutomirski
2018-01-19  4:15                   ` Van De Ven, Arjan
2018-01-19 15:47                     ` Andrea Arcangeli
2018-01-18 13:48 ` [PATCH 24/35] x86/msr: Move native_*msr macros out of microcode.h Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 25/35] x86/speculation: Add inlines to control Indirect Branch Speculation Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 26/35] x86/enter: Create macros to stop/restart " Peter Zijlstra, Peter Zijlstra
2018-01-18 19:44   ` Tim Chen
2018-01-18 13:48 ` [PATCH 27/35] x86/enter: Use IBRS on syscall and interrupts Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 28/35] x86/idle: Control Indirect Branch Speculation in idle Peter Zijlstra, Peter Zijlstra
2018-01-18 19:52   ` Andrew Cooper
2018-01-18 13:48 ` [PATCH 29/35] x86/speculation: Add IPBP support Peter Zijlstra, Peter Zijlstra
2018-01-18 16:22   ` Josh Poimboeuf
2018-01-18 18:31   ` Borislav Petkov
2018-01-18 18:35     ` Josh Poimboeuf
2018-01-18 18:46       ` Borislav Petkov
2018-01-18 13:48 ` [PATCH 30/35] x86/speculation: Use Indirect Branch Prediction Barrier in context switch Peter Zijlstra, Peter Zijlstra
2018-01-19  0:38   ` Tim Chen
2018-01-19  4:03     ` Kevin Easton
2018-01-19 20:26       ` Tim Chen [this message]
2018-01-18 13:48 ` [PATCH 31/35] x86/ibrs: Add new helper macros to save/restore MSR_IA32_SPEC_CTRL Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 32/35] x86/vmx: Direct access to MSR_IA32_SPEC_CTRL Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 33/35] x86/svm: " Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 34/35] x86/kvm: Add IBPB support Peter Zijlstra, Peter Zijlstra
2018-01-18 15:32   ` Paolo Bonzini
2018-01-19 15:25     ` Paolo Bonzini
2018-01-19 16:08       ` David Woodhouse
2018-01-19 16:27         ` Andy Lutomirski
2018-01-19 16:48         ` Paolo Bonzini
2018-01-18 13:48 ` [PATCH 35/35] x86/nospec: Add static assertions Peter Zijlstra, Peter Zijlstra

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