From: Andy Lutomirski <luto@kernel.org>
To: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>, 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 14:34:43 -0700 [thread overview]
Message-ID: <CALCETrUVUqK6_bjFNSmOjnWVNscwfWmMa6Bt9fQrpFa5m3xNwA@mail.gmail.com> (raw)
In-Reply-To: <b3defc91-1e8e-d0d5-2ac3-3861a7e3355c@intel.com>
On Tue, Sep 22, 2020 at 10:46 AM Yu, Yu-cheng <yu-cheng.yu@intel.com> wrote:
>
> On 9/21/2020 4:48 PM, Andy Lutomirski wrote:
> > On Mon, Sep 21, 2020 at 3:37 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> >>
> >> On Mon, 2020-09-21 at 09:22 -0700, Yu, Yu-cheng wrote:
>
> [...]
>
> >>
> >> Here is the patch:
> >>
> >> ------
> >>
> >> From dfdee39c795ee5dcee2c77f6ba344a61f4d8124b Mon Sep 17 00:00:00 2001
> >> From: Yu-cheng Yu <yu-cheng.yu@intel.com>
> >> Date: Thu, 29 Nov 2018 14:15:38 -0800
> >> Subject: [PATCH 34/43] x86/vsyscall/64: Fixup Shadow Stack and Indirect Branch
> >> Tracking for vsyscall emulation
> >>
> >> Vsyscall entry points are effectively branch targets. Mark them with
> >> ENDBR64 opcodes. When emulating the RET instruction, unwind the shadow
> >> stack and reset IBT state machine.
> >>
> >> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> >> ---
> >> arch/x86/entry/vsyscall/vsyscall_64.c | 29 +++++++++++++++++++++++
> >> arch/x86/entry/vsyscall/vsyscall_emu_64.S | 9 +++++++
> >> arch/x86/entry/vsyscall/vsyscall_trace.h | 1 +
> >> 3 files changed, 39 insertions(+)
> >>
> >> 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?
>
> Do you mean writing to the XSAVES area?
Yes.
>
> >
> >> +
> >> +#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.
> >
>
> At this point, the MSR's value can still be valid or is already saved to
> memory. If we are going to write to memory, then the MSR must be saved
> first. So I chose to do __fpregs_load_activate() and write the MSR.
>
> Maybe we can check the address before writing it to the MSR?
Performance is almost irrelevant here, and the writing-to-XSAVES-area
approach should have the benefit that the exception handling and
signaling happens for free.
next prev parent reply other threads:[~2020-09-23 21:35 UTC|newest]
Thread overview: 39+ 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
[not found] ` <9cf234db-d0f7-0466-be2c-afe04eb76759@intel.com>
2020-09-21 23:27 ` Yu, Yu-cheng
2020-09-21 22:52 ` Pavel Machek
2020-09-18 19:23 ` [PATCH v12 4/8] x86/cet/ibt: ELF header parsing for " 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
2020-09-23 21:29 ` Sean Christopherson
[not found] ` <a2e872ef-5539-c7c1-49ca-95d590f3b92a@intel.com>
[not found] ` <e7c20f4c-23a0-4a34-3895-c4f60993ec41@intel.com>
2020-09-23 22:20 ` Yu, Yu-cheng
2020-09-23 22:47 ` Andy Lutomirski
2020-09-23 22:53 ` Dave Hansen
[not found] ` <b3defc91-1e8e-d0d5-2ac3-3861a7e3355c@intel.com>
2020-09-23 21:34 ` Andy Lutomirski [this message]
2020-09-23 22:07 ` Yu, Yu-cheng
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