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From: Andy Lutomirski <luto@kernel.org>
To: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Brian Gerst <brgerst@gmail.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 02/18] x86/asm/64: Split the iret-to-user and iret-to-kernel paths
Date: Wed, 1 Nov 2017 04:32:43 -0700	[thread overview]
Message-ID: <CALCETrXUBUhxdLV4DT7_4n103FWPsP+q3wkVP2gPWgjEgM0Sqg@mail.gmail.com> (raw)
In-Reply-To: <20171027200447.GA12039@nazgul.tnic>

On Fri, Oct 27, 2017 at 1:04 PM, Borislav Petkov <bp@suse.de> wrote:
> On Thu, Oct 26, 2017 at 01:26:34AM -0700, Andy Lutomirski wrote:
>> These code paths will diverge soon.
>>
>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>> ---
>>  arch/x86/entry/entry_64.S        | 32 +++++++++++++++++++++++---------
>>  arch/x86/entry/entry_64_compat.S |  2 +-
>>  arch/x86/kernel/head_64.S        |  2 +-
>>  3 files changed, 25 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
>> index afe1f403fa0e..493e5e234d36 100644
>> --- a/arch/x86/entry/entry_64.S
>> +++ b/arch/x86/entry/entry_64.S
>> @@ -321,7 +321,7 @@ syscall_return_via_sysret:
>>
>>  opportunistic_sysret_failed:
>>       SWAPGS
>> -     jmp     restore_regs_and_iret
>> +     jmp     restore_regs_and_return_to_usermode
>
> rstor_regs_ret_user
>
> still sounds pretty ok to me and it is shorter and it is using the
> *RSTOR spelling the respective FPU insns use, so should be recognizable. :-)
>
> And the other one could be
>
> rstor_regs_ret_kernel
>
> of course.
>
>>  END(entry_SYSCALL_64)
>>
>>  ENTRY(stub_ptregs_64)
>> @@ -423,7 +423,7 @@ ENTRY(ret_from_fork)
>>       call    syscall_return_slowpath /* returns with IRQs disabled */
>>       TRACE_IRQS_ON                   /* user mode is traced as IRQS on */
>>       SWAPGS
>> -     jmp     restore_regs_and_iret
>> +     jmp     restore_regs_and_return_to_usermode
>>
>>  1:
>>       /* kernel thread */
>> @@ -612,7 +612,19 @@ GLOBAL(retint_user)
>>       call    prepare_exit_to_usermode
>>       TRACE_IRQS_IRETQ
>>       SWAPGS
>> -     jmp     restore_regs_and_iret
>> +
>> +GLOBAL(restore_regs_and_return_to_usermode)
>> +#ifdef CONFIG_DEBUG_ENTRY
>> +     testl   $3, CS(%rsp)
>
> testb
>
> ditto for the other spot.
>
>> +     jnz     1f
>> +     ud2
>> +1:
>> +#endif
>
> Why aren't we exploding here unconditionally? I mean, we don't want to
> return with RPL != 3 CS for whatever reason...

Performance?  I'll admit that both of these paths are extremely slow
no matter what, but it's nice to get a real dump if we screw it up.

I'll leave it as is for v2.  Feel free to argue more in v2 :)

  reply	other threads:[~2017-11-01 11:33 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-26  8:26 [PATCH 00/18] Pile o' entry/exit/sp0 changes Andy Lutomirski
2017-10-26  8:26 ` [PATCH 01/18] x86/asm/64: Remove the restore_c_regs_and_iret label Andy Lutomirski
2017-10-26 15:07   ` Borislav Petkov
2017-11-10  6:08   ` [01/18] " kemi
2017-10-26  8:26 ` [PATCH 02/18] x86/asm/64: Split the iret-to-user and iret-to-kernel paths Andy Lutomirski
2017-10-27 18:05   ` Dave Hansen
2017-11-01 11:34     ` Andy Lutomirski
2017-10-27 20:04   ` Borislav Petkov
2017-11-01 11:32     ` Andy Lutomirski [this message]
2017-10-26  8:26 ` [PATCH 03/18] x86/asm/64: Move SWAPGS into the common iret-to-usermode path Andy Lutomirski
2017-10-26 13:52   ` Brian Gerst
2017-10-26 14:13     ` Dave Hansen
2017-10-26 14:28       ` Borislav Petkov
2017-10-27 15:44         ` Andy Lutomirski
2017-10-27 18:08   ` Dave Hansen
2017-10-26  8:26 ` [PATCH 04/18] x86/asm/64: Simplify reg restore code in the standard IRET paths Andy Lutomirski
2017-10-26  8:26 ` [PATCH 05/18] x86/asm/64: Shrink paranoid_exit_restore and make labels local Andy Lutomirski
2017-10-27 20:07   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 06/18] x86/asm/64: Use pop instead of movq in syscall_return_via_sysret Andy Lutomirski
2017-10-27 20:11   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 07/18] x86/asm/64: Merge the fast and slow SYSRET paths Andy Lutomirski
2017-10-27 20:11   ` Borislav Petkov
2017-11-01 11:29     ` Andy Lutomirski
2017-11-01 12:35       ` Borislav Petkov
2017-11-01 17:26         ` Thomas Gleixner
2017-11-01 17:25   ` Brian Gerst
2017-11-01 20:35     ` Andy Lutomirski
2017-10-26  8:26 ` [PATCH 08/18] xen: add xen nmi trap entry Andy Lutomirski
2017-10-26  8:26 ` [PATCH 09/18] x86/asm/64: De-Xen-ify our NMI code Andy Lutomirski
2017-10-26  8:41   ` Juergen Gross
2017-10-27 20:11   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 10/18] x86/asm/32: Pull MSR_IA32_SYSENTER_CS update code out of native_load_sp0() Andy Lutomirski
2017-10-26 18:00   ` Brian Gerst
2017-10-27 13:51   ` Thomas Gleixner
2017-10-27 15:50     ` Andy Lutomirski
2017-10-27 20:11   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 11/18] x86/asm/64: Pass sp0 directly to load_sp0() Andy Lutomirski
2017-10-27 20:12   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 12/18] x86/asm: Add task_top_of_stack() to find the top of a task's stack Andy Lutomirski
2017-10-26  8:26 ` [PATCH 13/18] x86/xen/64: Clean up SP code in cpu_initialize_context() Andy Lutomirski
2017-10-26  8:43   ` Juergen Gross
2017-10-26  8:26 ` [PATCH 14/18] x86/boot/64: Stop initializing TSS.sp0 at boot Andy Lutomirski
2017-10-27 18:21   ` Dave Hansen
2017-10-28  8:10     ` Andy Lutomirski
2017-10-26  8:26 ` [PATCH 15/18] x86/asm/64: Remove all remaining direct thread_struct::sp0 reads Andy Lutomirski
2017-11-01 10:08   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 16/18] x86/boot/32: Fix cpu_current_top_of_stack initialization at boot Andy Lutomirski
2017-11-01 10:18   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 17/18] x86/asm/64: Remove thread_struct::sp0 Andy Lutomirski
2017-10-28  0:52   ` Brian Gerst
2017-11-01 10:23   ` Borislav Petkov
2017-11-01 10:40     ` Andy Lutomirski
2017-10-26  8:26 ` [PATCH 18/18] x86/traps: Use a new on_thread_stack() helper to clean up an assertion Andy Lutomirski
2017-11-01 10:31   ` Borislav Petkov
2017-11-01 10:45     ` Andy Lutomirski
2017-10-26 15:55 ` [PATCH 00/18] Pile o' entry/exit/sp0 changes Linus Torvalds
2017-10-28  7:31   ` Andy Lutomirski

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