From: Andrew Cooper <andrew.cooper3@citrix.com>
To: "Wu, Feng" <feng.wu@intel.com>, Jan Beulich <JBeulich@suse.com>,
xen-devel <xen-devel@lists.xenproject.org>
Cc: Keir Fraser <keir@xen.org>
Subject: Re: [PATCH 2/4] x86: suppress SMAP and SMEP while running 32-bit PV guest code
Date: Wed, 9 Mar 2016 12:33:10 +0000 [thread overview]
Message-ID: <56E01806.7020602@citrix.com> (raw)
In-Reply-To: <E959C4978C3B6342920538CF579893F00C36A370@SHSMSX104.ccr.corp.intel.com>
On 09/03/16 12:27, Wu, Feng wrote:
>
>> -----Original Message-----
>> From: Andrew Cooper [mailto:andrew.cooper3@citrix.com]
>> Sent: Wednesday, March 9, 2016 6:46 PM
>> To: Wu, Feng <feng.wu@intel.com>; Jan Beulich <JBeulich@suse.com>; xen-
>> devel <xen-devel@lists.xenproject.org>
>> Cc: Keir Fraser <keir@xen.org>
>> Subject: Re: [PATCH 2/4] x86: suppress SMAP and SMEP while running 32-bit PV
>> guest code
>>
>> On 09/03/16 08:09, Wu, Feng wrote:
>>
>>>> --- a/xen/arch/x86/x86_64/entry.S
>>>> +++ b/xen/arch/x86/x86_64/entry.S
>>>> @@ -434,6 +434,7 @@ ENTRY(dom_crash_sync_extable)
>>>>
>>>> ENTRY(common_interrupt)
>>>> SAVE_ALL CLAC
>>>> + SMEP_SMAP_RESTORE
>>>> movq %rsp,%rdi
>>>> callq do_IRQ
>>>> jmp ret_from_intr
>>>> @@ -454,13 +455,64 @@ ENTRY(page_fault)
>>>> GLOBAL(handle_exception)
>>>> SAVE_ALL CLAC
>>>> handle_exception_saved:
>>>> + GET_CURRENT(%rbx)
>>>> testb $X86_EFLAGS_IF>>8,UREGS_eflags+1(%rsp)
>>>> jz exception_with_ints_disabled
>>>> - sti
>>>> +
>>>> +.Lsmep_smap_orig:
>>>> + jmp 0f
>>>> + .if 0 // GAS bug (affecting at least 2.22 ... 2.26)
>>>> + .org .Lsmep_smap_orig + (.Lsmep_smap_alt_end - .Lsmep_smap_alt),
>> 0xcc
>>>> + .else
>>>> + // worst case: rex + opcode + modrm + 4-byte displacement
>>>> + .skip (1 + 1 + 1 + 4) - 2, 0xcc
>>>> + .endif
>>>> + .pushsection .altinstr_replacement, "ax"
>>>> +.Lsmep_smap_alt:
>>>> + mov VCPU_domain(%rbx),%rax
>>>> +.Lsmep_smap_alt_end:
>>>> + .section .altinstructions, "a"
>>>> + altinstruction_entry .Lsmep_smap_orig, .Lsmep_smap_alt, \
>>>> + X86_FEATURE_SMEP, \
>>>> + (.Lsmep_smap_alt_end - .Lsmep_smap_alt), \
>>>> + (.Lsmep_smap_alt_end - .Lsmep_smap_alt)
>>>> + altinstruction_entry .Lsmep_smap_orig, .Lsmep_smap_alt, \
>>>> + X86_FEATURE_SMAP, \
>>>> + (.Lsmep_smap_alt_end - .Lsmep_smap_alt), \
>>>> + (.Lsmep_smap_alt_end - .Lsmep_smap_alt)
>>>> + .popsection
>>>> +
>>>> + testb $3,UREGS_cs(%rsp)
>>>> + jz 0f
>>>> + cmpb $0,DOMAIN_is_32bit_pv(%rax)
>>>> + je 0f
>>>> + call cr4_smep_smap_restore
>>>> + /*
>>>> + * An NMI or #MC may occur between clearing CR4.SMEP and
>> CR4.SMAP in
>>> Do you mean "before" when you typed "between" above?
>> The meaning is "between (clearing CR4.SMEP and CR4.SMAP in
>> compat_restore_all_guest) and (it actually returning to guest)"
>>
>> Nested lists in English are a source of confusion, even to native speakers.
> Oh, thanks for the clarification! Do you know how "An NMI or #MC may occur
> between clearing CR4.SMEP and CR4.SMAP in compat_restore_all_guest and
> it actually returning to guest context, in which case the guest would run with
> the two features enabled. " can happen? Especially how the guest can run
> with the two features enabled?
NMIs and MCEs can occur at any point, even if interrupts are disabled.
The bad situation is this sequence:
* Xen is returning to the guest and disables CR4.SMEP/SMAP
* NMI occurs while still in Xen
* NMI exit path sees it is returning to Xen and re-enabled CR4.SMEP/SMAP
* Xen ends up returning to guest with CR4.SMEP/SMAP enabled.
~Andrew
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next prev parent reply other threads:[~2016-03-09 12:33 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-04 11:08 [PATCH 0/4] x86: accommodate 32-bit PV guests with SMAP/SMEP handling Jan Beulich
2016-03-04 11:27 ` [PATCH 1/4] x86/alternatives: correct near branch check Jan Beulich
2016-03-07 15:43 ` Andrew Cooper
2016-03-07 15:56 ` Jan Beulich
2016-03-07 16:11 ` Andrew Cooper
2016-03-07 16:21 ` Jan Beulich
2016-03-08 17:33 ` Andrew Cooper
2016-03-04 11:27 ` [PATCH 2/4] x86: suppress SMAP and SMEP while running 32-bit PV guest code Jan Beulich
2016-03-07 16:59 ` Andrew Cooper
2016-03-08 7:57 ` Jan Beulich
2016-03-09 8:09 ` Wu, Feng
2016-03-09 14:09 ` Jan Beulich
2016-03-09 11:19 ` Andrew Cooper
2016-03-09 14:28 ` Jan Beulich
2016-03-09 8:09 ` Wu, Feng
2016-03-09 10:45 ` Andrew Cooper
2016-03-09 12:27 ` Wu, Feng
2016-03-09 12:33 ` Andrew Cooper [this message]
2016-03-09 12:36 ` Jan Beulich
2016-03-09 12:54 ` Wu, Feng
2016-03-09 13:35 ` Wu, Feng
2016-03-09 13:42 ` Andrew Cooper
2016-03-09 14:03 ` Jan Beulich
2016-03-09 14:07 ` Jan Beulich
2016-03-04 11:28 ` [PATCH 3/4] x86: use optimal NOPs to fill the SMAP/SMEP placeholders Jan Beulich
2016-03-07 17:43 ` Andrew Cooper
2016-03-08 8:02 ` Jan Beulich
2016-03-04 11:29 ` [PATCH 4/4] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
2016-03-07 17:45 ` Andrew Cooper
2016-03-10 9:44 ` [PATCH v2 0/3] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Jan Beulich
2016-03-10 9:53 ` [PATCH v2 1/3] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-05-13 15:48 ` Andrew Cooper
2016-03-10 9:54 ` [PATCH v2 2/3] x86: use optimal NOPs to fill the SMEP/SMAP placeholders Jan Beulich
2016-05-13 15:49 ` Andrew Cooper
2016-03-10 9:55 ` [PATCH v2 3/3] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
[not found] ` <56E9A0DB02000078000DD54C@prv-mh.provo.novell.com>
2016-03-17 7:50 ` [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Jan Beulich
2016-03-17 8:02 ` [PATCH v3 1/4] x86: move cached CR4 value to struct cpu_info Jan Beulich
2016-03-17 16:20 ` Andrew Cooper
2016-03-17 8:03 ` [PATCH v3 2/4] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-03-25 18:01 ` Konrad Rzeszutek Wilk
2016-03-29 6:55 ` Jan Beulich
2016-05-13 15:58 ` Andrew Cooper
2016-03-17 8:03 ` [PATCH v3 3/4] x86: use optimal NOPs to fill the SMEP/SMAP placeholders Jan Beulich
2016-05-13 15:57 ` Andrew Cooper
2016-05-13 16:06 ` Jan Beulich
2016-05-13 16:09 ` Andrew Cooper
2016-03-17 8:04 ` [PATCH v3 4/4] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
2016-03-25 18:02 ` Konrad Rzeszutek Wilk
2016-03-17 16:14 ` [PATCH v3 5/4] x86: reduce code size of struct cpu_info member accesses Jan Beulich
2016-03-25 18:47 ` Konrad Rzeszutek Wilk
2016-03-29 6:59 ` Jan Beulich
2016-03-30 14:28 ` Konrad Rzeszutek Wilk
2016-03-30 14:42 ` Jan Beulich
2016-05-13 16:11 ` Andrew Cooper
2016-05-03 13:58 ` Ping: [PATCH v3 2/4] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-05-03 14:10 ` Andrew Cooper
2016-05-03 14:25 ` Jan Beulich
2016-05-04 10:03 ` Andrew Cooper
2016-05-04 13:35 ` Jan Beulich
2016-05-04 3:07 ` Wu, Feng
2016-05-13 15:21 ` Wei Liu
2016-05-13 15:30 ` Jan Beulich
2016-05-13 15:33 ` Wei Liu
2016-05-13 17:02 ` [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Wei Liu
2016-05-13 17:21 ` Andrew Cooper
2016-06-21 6:19 ` Wu, Feng
2016-06-21 7:17 ` Jan Beulich
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