From: Andy Lutomirski <luto@kernel.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
Borislav Petkov <bpetkov@suse.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Brian Gerst <brgerst@gmail.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 04:34:05 -0700 [thread overview]
Message-ID: <CALCETrU9qTrwfKW0_f5WzG1QTC2yEFxd40G_z7CtY+wwutiyNQ@mail.gmail.com> (raw)
In-Reply-To: <1acdc314-6568-bada-6bea-4fa6ca21fb91@intel.com>
On Fri, Oct 27, 2017 at 11:05 AM, Dave Hansen <dave.hansen@intel.com> wrote:
> On 10/26/2017 01:26 AM, Andy Lutomirski wrote:
>> +GLOBAL(restore_regs_and_return_to_usermode)
>> +#ifdef CONFIG_DEBUG_ENTRY
>> + testl $3, CS(%rsp)
>> + jnz 1f
>> + ud2
>
> A nit from the mere mortals in the audience: Could we start commenting
> or make a constant for the user segment bits in CS?
Yeah. We have such a define, but it's not currently usable from asm.
Also, we can't do the obvious:
testl $SEGMENT_RPL_MASK, ...
jump_if_not_equal_to_KERNEL_RPL
because that makes no sense in asm :(
>
> Also, it would be nice to explain what's going on here. Maybe:
>
> /*
> * We think we are returning to the kernel. Check the
> * registers we are about to restore and if we appear to
> * be returning to userspace, do something that will cause
> * a fault and hopefully an oops report.
> */
>
> Otherwise, I really like this change. It's really hard to figure out
> what the context is in the entry assembly in a lot of cases. It's a
> place where code reuse actually makes things harder to follow.
next prev parent reply other threads:[~2017-11-01 11:34 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 [this message]
2017-10-27 20:04 ` Borislav Petkov
2017-11-01 11:32 ` Andy Lutomirski
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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