From: Andy Lutomirski <luto@kernel.org>
To: David Laight <David.Laight@aculab.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Jarkko Nikula <jarkko.nikula@linux.intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled
Date: Wed, 29 Nov 2017 08:22:49 -0800 [thread overview]
Message-ID: <CALCETrWndxkJebKbxdCUVpa0_CkW9QdaMbE-d5M=XEw_JFG3YQ@mail.gmail.com> (raw)
In-Reply-To: <4f2c1cf45fd04e83a7d360d0d602830e@AcuMS.aculab.com>
On Wed, Nov 29, 2017 at 6:56 AM, David Laight <David.Laight@aculab.com> wrote:
> From: Andy Lutomirski
>> Sent: 29 November 2017 14:34
>> > On Nov 29, 2017, at 4:47 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>> >
>> >> On Wed, Nov 29, 2017 at 08:09:51AM +0100, Ingo Molnar wrote:
>> >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
>> >> index f81d50d7ceac..c0b52df8ee4f 100644
>> >> --- a/arch/x86/entry/entry_64.S
>> >> +++ b/arch/x86/entry/entry_64.S
>> >> @@ -945,16 +945,16 @@ idtentry simd_coprocessor_error do_simd_coprocessor_error
>> has_error_code=0
>> >> */
>> >> ENTRY(native_load_gs_index)
>> >> FRAME_BEGIN
>> >> + SWAPGS /* switch from user GS to kernel GS */
>> >> pushfq
>> >> DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
>> >> TRACE_IRQS_OFF
>> >> - SWAPGS
>> >
>> > I'm thinking those moves it too far back; we should at least have
>> > interrupts disabled when we do SWAPGS, no? Also, curse paravirt.
>> >
>>
>> I'll look in a few hours.
>>
>> But we definitely can't have irqs on when running with user gs.
>
> I can't remember what happens when swapgs itself faults.
> I'm pretty sure it can, restoring %ds %es and %fs can definitely fault
> (especially for 32 bit apps) if the restored values are invalid.
> With user LDT I think it is possible for a valid segment register
> to become invalid while a process is sleeping.
> The debugger (and possible a signal handler) can set the segment
> registers to arbitrary values - so loading them faults.
>
> I fixed NetBSD a few years ago so that all these faults were handled
> correctly.
SWAPGS never faults.
I did test my patch, and I'm wondering how I missed the problem. Looking now...
next prev parent reply other threads:[~2017-11-29 16:23 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-28 14:35 Suspend-to-ram/resume regression with commit ca37e57bbe0c Jarkko Nikula
2017-11-29 7:09 ` [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled Ingo Molnar
2017-11-29 9:25 ` Jarkko Nikula
2017-11-29 9:28 ` Thomas Gleixner
2017-11-29 12:39 ` Jarkko Nikula
2017-11-29 12:47 ` Peter Zijlstra
2017-11-29 14:33 ` Andy Lutomirski
2017-11-29 14:56 ` David Laight
2017-11-29 16:22 ` Andy Lutomirski [this message]
2017-11-29 16:51 ` David Laight
2017-11-29 20:48 ` Linus Torvalds
2017-11-29 16:51 ` Andy Lutomirski
2017-11-29 17:57 ` Andy Lutomirski
2017-11-29 18:08 ` Peter Zijlstra
2017-11-29 18:12 ` Andy Lutomirski
2017-11-29 20:58 ` Linus Torvalds
2017-11-29 21:25 ` Andy Lutomirski
2017-11-29 21:41 ` Andy Lutomirski
2017-11-29 21:57 ` Andy Lutomirski
2017-11-30 8:42 ` Jarkko Nikula
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