From: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>,
Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
linux-arch <linux-arch@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
Dave Martin <Dave.Martin@arm.com>,
Weijiang Yang <weijiang.yang@intel.com>
Subject: Re: [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled
Date: Wed, 23 Sep 2020 15:06:44 -0700 [thread overview]
Message-ID: <a2e872ef-5539-c7c1-49ca-95d590f3b92a@intel.com> (raw)
In-Reply-To: <20200923212925.GC15101@linux.intel.com>
On 9/23/2020 2:29 PM, Sean Christopherson wrote:
> On Mon, Sep 21, 2020 at 04:48:25PM -0700, Andy Lutomirski wrote:
>> On Mon, Sep 21, 2020 at 3:37 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>>> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c
>>> b/arch/x86/entry/vsyscall/vsyscall_64.c
>>> index 44c33103a955..0131c9f7f9c5 100644
>>> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
>>> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
>>> @@ -38,6 +38,9 @@
>>> #include <asm/fixmap.h>
>>> #include <asm/traps.h>
>>> #include <asm/paravirt.h>
>>> +#include <asm/fpu/xstate.h>
>>> +#include <asm/fpu/types.h>
>>> +#include <asm/fpu/internal.h>
>>>
>>> #define CREATE_TRACE_POINTS
>>> #include "vsyscall_trace.h"
>>> @@ -286,6 +289,32 @@ bool emulate_vsyscall(unsigned long error_code,
>>> /* Emulate a ret instruction. */
>>> regs->ip = caller;
>>> regs->sp += 8;
>>> +
>>> + if (current->thread.cet.shstk_size ||
>>> + current->thread.cet.ibt_enabled) {
>>> + u64 r;
>>> +
>>> + fpregs_lock();
>>> + if (test_thread_flag(TIF_NEED_FPU_LOAD))
>>> + __fpregs_load_activate();
>>
>> Wouldn't this be nicer if you operated on the memory image, not the registers?
>>
>>> +
>>> +#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
>>> + /* Fixup branch tracking */
>>> + if (current->thread.cet.ibt_enabled) {
>>> + rdmsrl(MSR_IA32_U_CET, r);
>>> + wrmsrl(MSR_IA32_U_CET, r & ~CET_WAIT_ENDBR);
>>> + }
>>> +#endif
>>
>> Seems reasonable on first glance.
>>
>>> +
>>> +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
>>> + /* Unwind shadow stack. */
>>> + if (current->thread.cet.shstk_size) {
>>> + rdmsrl(MSR_IA32_PL3_SSP, r);
>>> + wrmsrl(MSR_IA32_PL3_SSP, r + 8);
>>> + }
>>> +#endif
>>
>> What happens if the result is noncanonical? A quick skim of the SDM
>> didn't find anything. This latter issue goes away if you operate on
>> the memory image, though -- writing a bogus value is just fine, since
>> the FP restore will handle it.
>
> #GP, the SSP MSRs do canonical checks.
I think I'll add a check here for (r + 8) >= TASK_SIZE_MAX. It is
better than getting a fault.
Thanks,
Yu-cheng
next prev parent reply other threads:[~2020-09-23 22:06 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-18 19:23 [PATCH v12 0/8] Control-flow Enforcement: Indirect Branch Tracking Yu-cheng Yu
2020-09-18 19:23 ` [PATCH v12 1/8] x86/cet/ibt: Add Kconfig option for user-mode " Yu-cheng Yu
2020-09-18 20:24 ` Randy Dunlap
2020-09-18 20:59 ` Pavel Machek
2020-09-18 21:08 ` H.J. Lu
2020-09-18 21:24 ` Pavel Machek
2020-09-18 21:36 ` H.J. Lu
2020-09-18 21:25 ` Yu, Yu-cheng
2020-09-18 21:40 ` Pavel Machek
2020-09-18 21:46 ` H.J. Lu
2020-09-18 22:03 ` Pavel Machek
2020-09-21 22:30 ` Yu, Yu-cheng
2020-09-21 22:41 ` Dave Hansen
2020-09-21 22:47 ` Yu, Yu-cheng
2020-09-21 22:54 ` Dave Hansen
2020-09-21 23:27 ` Yu, Yu-cheng
2020-09-21 22:52 ` Pavel Machek
2020-09-21 22:58 ` Dave Hansen
2020-09-18 19:23 ` [PATCH v12 2/8] x86/cet/ibt: User-mode Indirect Branch Tracking support Yu-cheng Yu
2020-09-18 19:23 ` [PATCH v12 3/8] x86/cet/ibt: Handle signals for Indirect Branch Tracking Yu-cheng Yu
2020-09-18 19:23 ` [PATCH v12 4/8] x86/cet/ibt: ELF header parsing " Yu-cheng Yu
2020-09-18 19:23 ` [PATCH v12 5/8] x86/cet/ibt: Update arch_prctl functions " Yu-cheng Yu
2020-09-18 19:23 ` [PATCH v12 6/8] x86/vdso/32: Add ENDBR32 to __kernel_vsyscall entry point Yu-cheng Yu
2020-09-18 19:23 ` [PATCH v12 7/8] x86/vdso: Insert endbr32/endbr64 to vDSO Yu-cheng Yu
2020-09-18 19:23 ` [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled Yu-cheng Yu
2020-09-18 19:32 ` Dave Hansen
2020-09-18 21:00 ` Pavel Machek
2020-09-18 21:06 ` H.J. Lu
2020-09-18 21:17 ` Dave Hansen
2020-09-18 21:22 ` H.J. Lu
2020-09-18 21:28 ` Dave Hansen
2020-09-18 21:21 ` Yu, Yu-cheng
2020-09-18 21:22 ` Pavel Machek
2020-09-19 0:11 ` Andy Lutomirski
2020-09-21 16:22 ` Yu, Yu-cheng
2020-09-21 22:37 ` Yu-cheng Yu
2020-09-21 23:48 ` Andy Lutomirski
2020-09-22 17:45 ` Yu, Yu-cheng
2020-09-23 21:34 ` Andy Lutomirski
2020-09-23 22:07 ` Yu, Yu-cheng
2020-09-23 21:29 ` Sean Christopherson
2020-09-23 22:06 ` Yu, Yu-cheng [this message]
2020-09-23 22:08 ` Dave Hansen
2020-09-23 22:20 ` Yu, Yu-cheng
2020-09-23 22:47 ` Andy Lutomirski
2020-09-23 22:53 ` Dave Hansen
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