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From: David Woodhouse <dwmw2@infradead.org>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH v6.5 11/26] x86: Support indirect thunks from assembly code
Date: Thu, 11 Jan 2018 13:46:55 +0000	[thread overview]
Message-ID: <1515678415.22302.342.camel@infradead.org> (raw)
In-Reply-To: <f3e145f0-6d53-a479-e536-d3e1a3e9fd87@citrix.com>


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On Thu, 2018-01-11 at 13:41 +0000, Andrew Cooper wrote:
> On 11/01/18 13:03, David Woodhouse wrote:
> > 
> > On Thu, 2018-01-04 at 00:15 +0000, Andrew Cooper wrote:
> > > 
> > > +         * We've got no usable stack so can't use a RETPOLINE thunk, and are
> > > +         * further than +- 2G from the high mappings so couldn't use JUMP_THUNK
> > > +         * even if was a non-RETPOLINE thunk.  Futhermore, an LFENCE isn't
> > > +         * necesserily safe to use at this point.
>
> > I count three typos, pedantry about ± and GiB aside.
> > Late night? :)
> Just one of many...
> 
> I've found furthermore and necessarily.  Where is the 3rd?

* even if IT was a … 


> > > -        asm volatile ( "call *%[stb]\n"
> > > +        asm volatile ( "CALL_THUNK %[stb]\n"
> > If you make that %V[stb] then...
> > ... you don't need this.
> That's fine in principle, except it isn't compatible with most of the
> compilers we support.  To use, the %V has to be hidden behind a
> conditional macro, and I can't think of any remotely-clean way to do
> that.

In at least one incarnation I ended up with something like

#ifndef CONFIG_RETPOLINE
#define CALL_THUNK(reg) "call *%[" #reg "]"
#else
#define CALL_THUNK(reg) "CALL_THUNK %V[" #reg "]"
#endif

Or maybe I just insisted that it was called %[thunk_target] and my
CALL_THUNK C macro doesn't even take an argument. I forget. Late night…

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  reply	other threads:[~2018-01-11 13:46 UTC|newest]

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-04  0:15 [PATCH v6.5 00/26] x86: Mitigations for SP2/CVE-2017-5715/Branch Target Injection Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 01/26] x86/alt: Break out alternative-asm into a separate header file Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 02/26] x86/alt: Introduce ALTERNATIVE{, _2} macros Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 03/26] x86/hvm: Rename update_guest_vendor() callback to cpuid_policy_changed() Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 04/26] x86: Introduce a common cpuid_policy_updated() Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 05/26] x86/entry: Remove support for partial cpu_user_regs frames Andrew Cooper
2018-01-04  8:51   ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 06/26] x86/entry: Rearrange RESTORE_ALL to restore register in stack order Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 07/26] x86/hvm: Use SAVE_ALL to construct the cpu_user_regs frame after VMExit Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 08/26] x86/entry: Erase guest GPR state on entry to Xen Andrew Cooper
2018-01-22 10:04   ` David Woodhouse
2018-01-22 10:18     ` Andrew Cooper
2018-01-22 10:27       ` David Woodhouse
2018-01-04  0:15 ` [PATCH v6.5 09/26] x86: Support compiling with indirect branch thunks Andrew Cooper
2018-01-04  9:02   ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 10/26] common/wait: Clarifications to wait infrastructure Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 11/26] x86: Support indirect thunks from assembly code Andrew Cooper
2018-01-04  9:23   ` Jan Beulich
2018-01-08 18:24     ` Andrew Cooper
2018-01-09  8:36       ` Jan Beulich
2018-01-09 11:23         ` Andrew Cooper
2018-01-09 13:18           ` Jan Beulich
2018-01-11 13:03   ` David Woodhouse
2018-01-11 13:41     ` Andrew Cooper
2018-01-11 13:46       ` David Woodhouse [this message]
2018-01-04  0:15 ` [PATCH v6.5 12/26] x86/boot: Report details of speculative mitigations Andrew Cooper
2018-01-04  9:29   ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 13/26] x86/amd: Try to set lfence as being Dispatch Serialising Andrew Cooper
2018-01-04  9:32   ` Jan Beulich
2018-01-08 19:01     ` Andrew Cooper
2018-01-09  8:38       ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 14/26] x86: Introduce alternative indirect thunks Andrew Cooper
2018-01-04  9:40   ` Jan Beulich
2018-01-09 11:44     ` Andrew Cooper
2018-01-09 13:24       ` Jan Beulich
2018-01-09 13:30         ` Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 15/26] x86/feature: Definitions for Indirect Branch Controls Andrew Cooper
2018-01-04  1:14   ` Doug Goldstein
2018-01-04  1:16     ` Andrew Cooper
2018-01-04  4:05     ` Anthony Liguori
2018-01-04  9:42   ` Jan Beulich
2018-01-04 18:51   ` Wei Liu
2018-01-04  0:15 ` [PATCH v6.5 16/26] x86/cmdline: Introduce a command line option to disable IBRS/IBPB, STIBP and IBPB Andrew Cooper
2018-01-04  9:43   ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 17/26] x86/msr: Emulation of MSR_{SPEC_CTRL, PRED_CMD} for guests Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 18/26] x86/migrate: Move MSR_SPEC_CTRL on migrate Andrew Cooper
2018-01-04  0:15 ` [PATCH v6.5 19/26] x86/hvm: Permit guests direct access to MSR_{SPEC_CTRL, PRED_CMD} Andrew Cooper
2018-01-04  9:52   ` Jan Beulich
2018-01-09 12:03     ` Andrew Cooper
2018-01-09 13:28       ` Jan Beulich
2018-01-09 13:34         ` Andrew Cooper
2018-01-09 13:58           ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 20/26] x86: Protect unaware domains from meddling hyperthreads Andrew Cooper
2018-01-04  9:59   ` Jan Beulich
2018-01-09 14:21     ` Andrew Cooper
2018-01-09 14:29       ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 21/26] x86/entry: Use MSR_SPEC_CTRL at each entry/exit point Andrew Cooper
2018-01-04 10:14   ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 22/26] x86/boot: Calculate the most appropriate BTI mitigation to use Andrew Cooper
2018-01-04 10:17   ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 23/26] x86/entry: Clobber the Return Stack Buffer on entry to Xen Andrew Cooper
2018-01-04 10:22   ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 24/26] x86/ctxt: Issue a speculation barrier between vcpu contexts Andrew Cooper
2018-01-04 10:25   ` Jan Beulich
2018-01-04  0:15 ` [PATCH v6.5 25/26] x86/cpuid: Offer Indirect Branch Controls to guests Andrew Cooper
2018-01-09 11:44   ` Wei Liu
2018-01-04  0:15 ` [PATCH v6.5 26/26] x86/idle: Clear SPEC_CTRL while idle Andrew Cooper
2018-01-04 10:29   ` Jan Beulich
2018-01-04 10:41   ` Jan Beulich

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