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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 08/26] x86/entry: Erase guest GPR state on entry to Xen
Date: Mon, 22 Jan 2018 10:27:36 +0000	[thread overview]
Message-ID: <1516616856.9814.152.camel@infradead.org> (raw)
In-Reply-To: <8ca02d70-46c2-fd71-05d8-dc53fbccc437@citrix.com>


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On Mon, 2018-01-22 at 10:18 +0000, Andrew Cooper wrote:
> On 22/01/2018 10:04, David Woodhouse wrote:
> > 
> > On Thu, 2018-01-04 at 00:15 +0000, Andrew Cooper wrote:
> > > 
> > > --- a/xen/include/asm-x86/asm_defns.h
> > > +++ b/xen/include/asm-x86/asm_defns.h
> > > @@ -217,22 +217,34 @@ static always_inline void stac(void)
> > >          addq  $-(UREGS_error_code-UREGS_r15), %rsp
> > >          cld
> > >          movq  %rdi,UREGS_rdi(%rsp)
> > > +        xor   %edi, %edi
> > >          movq  %rsi,UREGS_rsi(%rsp)
> > > +        xor   %esi, %esi
> > >          movq  %rdx,UREGS_rdx(%rsp)
> > > +        xor   %edx, %edx
> > >          movq  %rcx,UREGS_rcx(%rsp)
> > > +        xor   %ecx, %ecx
> > >          movq  %rax,UREGS_rax(%rsp)
> > > +        xor   %eax, %eax
> > You didn't want to erase all 64 bits?
>
> This does erase all 64 bits.  (We're in long mode, so the upper 32 bits
> are implicitly zeroed, without an added rex prefix.)

Eww. In the grand scheme of things, I'd rather the assembler knew that
(and happily omitted the rex prefix all by itself to use the more
efficient encoding of the instruction), and not me.

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  reply	other threads:[~2018-01-22 10:27 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 [this message]
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
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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