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From: Borislav Petkov <bp@suse.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: 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 v2 02/20] x86/asm/64: Split the iret-to-user and iret-to-kernel paths
Date: Thu, 2 Nov 2017 11:50:18 +0100	[thread overview]
Message-ID: <20171102105018.gdpjhixuf2f5v5e5@pd.tnic> (raw)
In-Reply-To: <dccf8c7b3750199b4b30383c812d4e2931811509.1509609304.git.luto@kernel.org>

On Thu, Nov 02, 2017 at 12:58:59AM -0700, Andy Lutomirski wrote:
> These code paths will diverge soon.
> 
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>  arch/x86/entry/entry_64.S        | 34 +++++++++++++++++++++++++---------
>  arch/x86/entry/entry_64_compat.S |  2 +-
>  arch/x86/kernel/head_64.S        |  2 +-
>  3 files changed, 27 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index afe1f403fa0e..07fe816f0d28 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
>  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 +612,20 @@ 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
> +	/* Assert that pt_regs indicates user mode. */
> +	testl	$3, CS(%rsp)
> +	jnz	1f
> +	ud2
> +1:
> +#endif

Here's me arguing in v2:

If these paths are slow and adding a TEST and a Jcc would give us the
additional sanity-checking, then I don't see any downside to it.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

  parent reply	other threads:[~2017-11-02 10:50 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-02  7:58 [PATCH v2 00/20] Pile o' entry/exit/sp0 changes Andy Lutomirski
2017-11-02  7:58 ` [PATCH v2 01/20] x86/asm/64: Remove the restore_c_regs_and_iret label Andy Lutomirski
2017-11-02 10:49   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:58 ` [PATCH v2 02/20] x86/asm/64: Split the iret-to-user and iret-to-kernel paths Andy Lutomirski
2017-11-02 10:49   ` [tip:x86/asm] x86/entry/64: Split the IRET-to-user and IRET-to-kernel paths tip-bot for Andy Lutomirski
2017-11-02 10:50   ` Borislav Petkov [this message]
2017-11-02 12:09     ` [PATCH] x86/entry/64: Shorten TEST instructions Borislav Petkov
2017-11-02 12:48       ` [tip:x86/asm] " tip-bot for Borislav Petkov
2017-11-02  7:59 ` [PATCH v2 03/20] x86/asm/64: Move SWAPGS into the common iret-to-usermode path Andy Lutomirski
2017-11-02 10:49   ` [tip:x86/asm] x86/entry/64: Move SWAPGS into the common IRET-to-usermode path tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 04/20] x86/asm/64: Simplify reg restore code in the standard IRET paths Andy Lutomirski
2017-11-02 10:50   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 05/20] x86/asm/64: Shrink paranoid_exit_restore and make labels local Andy Lutomirski
2017-11-02 10:50   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 06/20] x86/asm/64: Use pop instead of movq in syscall_return_via_sysret Andy Lutomirski
2017-11-02 10:51   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 07/20] x86/asm/64: Merge the fast and slow SYSRET paths Andy Lutomirski
2017-11-02 10:51   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 08/20] x86/entry/64: Use POP instead of MOV to restore regs on NMI return Andy Lutomirski
2017-11-02 10:51   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 09/20] x86/entry/64: Remove the RESTORE_..._REGS infrastructure Andy Lutomirski
2017-11-02 10:52   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 10/20] xen: add xen nmi trap entry Andy Lutomirski
2017-11-02 10:52   ` [tip:x86/asm] xen, x86/entry/64: Add xen NMI " tip-bot for Juergen Gross
2017-11-02  7:59 ` [PATCH v2 11/20] x86/asm/64: De-Xen-ify our NMI code Andy Lutomirski
2017-11-02 10:53   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 12/20] x86/asm/32: Pull MSR_IA32_SYSENTER_CS update code out of native_load_sp0() Andy Lutomirski
2017-11-02 10:53   ` [tip:x86/asm] x86/entry/32: Pull the " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 13/20] x86/asm/64: Pass sp0 directly to load_sp0() Andy Lutomirski
2017-11-02  9:48   ` Ingo Molnar
2017-11-02  9:53     ` Ingo Molnar
2017-11-02 10:32     ` Andy Lutomirski
2017-11-02 10:53   ` [tip:x86/asm] x86/entry/64: Pass SP0 " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 14/20] x86/asm: Add task_top_of_stack() to find the top of a task's stack Andy Lutomirski
2017-11-02 10:54   ` [tip:x86/asm] x86/entry: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 15/20] x86/xen/64: Clean up SP code in cpu_initialize_context() Andy Lutomirski
2017-11-02  9:56   ` Juergen Gross
2017-11-02 10:54   ` [tip:x86/asm] x86/xen/64, x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 16/20] x86/boot/64: Stop initializing TSS.sp0 at boot Andy Lutomirski
2017-11-02 10:55   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 17/20] x86/asm/64: Remove all remaining direct thread_struct::sp0 reads Andy Lutomirski
2017-11-02 10:55   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 18/20] x86/boot/32: Fix cpu_current_top_of_stack initialization at boot Andy Lutomirski
2017-11-02 10:56   ` [tip:x86/asm] x86/entry/32: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 19/20] x86/asm/64: Remove thread_struct::sp0 Andy Lutomirski
2017-11-02 10:56   ` [tip:x86/asm] x86/entry/64: " tip-bot for Andy Lutomirski
2017-11-02  7:59 ` [PATCH v2 20/20] x86/traps: Use a new on_thread_stack() helper to clean up an assertion Andy Lutomirski
2017-11-02 10:56   ` [tip:x86/asm] " tip-bot for Andy Lutomirski

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