From: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
To: 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>,
Pengfei Xu <pengfei.xu@intel.com>
Subject: Re: [PATCH v13 8/8] x86/vsyscall/64: Fixup Shadow Stack and Indirect Branch Tracking for vsyscall emulation
Date: Mon, 28 Sep 2020 12:04:24 -0700 [thread overview]
Message-ID: <054bd574-1566-2be4-b542-884500b7319d@intel.com> (raw)
In-Reply-To: <CALCETrWuhPE3A7eWC=ERJa7i7jLtsXnfu04PKUFJ-Gybro+p=Q@mail.gmail.com>
On 9/28/2020 10:37 AM, Andy Lutomirski wrote:
> On Mon, Sep 28, 2020 at 9:59 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>>
>> On Fri, 2020-09-25 at 09:51 -0700, Andy Lutomirski wrote:
>>>> On Sep 25, 2020, at 9:48 AM, Yu, Yu-cheng <yu-cheng.yu@intel.com> wrote:
>> +
>> + cet = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER);
>> + if (!cet) {
>> + /*
>> + * This is an unlikely case where the task is
>> + * CET-enabled, but CET xstate is in INIT.
>> + */
>> + WARN_ONCE(1, "CET is enabled, but no xstates");
>
> "unlikely" doesn't really cover this.
>
>> + fpregs_unlock();
>> + goto sigsegv;
>> + }
>> +
>> + if (cet->user_ssp && ((cet->user_ssp + 8) < TASK_SIZE_MAX))
>> + cet->user_ssp += 8;
>
> This looks buggy. The condition should be "if SHSTK is on, then add 8
> to user_ssp". If the result is noncanonical, then some appropriate
> exception should be generated, probably by the FPU restore code -- see
> below. You should be checking the SHSTK_EN bit, not SSP.
The code now checks if shadow stack is on (yes, it should check SHSTK_EN
bit, I will fix it.), then adds 8 to user_ssp. If the result is
canonical, then it sets the corresponding xstate.
If the resulting address is not canonical, the kernel does not know what
the address should be either. I think the best action to take is doing
nothing about the shadow stack pointer, and let the application return
and get a control protection fault. The application should have not got
into such situation in the first place; if it does, it should fault.
>
> Also, can you point me to where any of these canonicality rules are
> documented in the SDM? I looked and I can't find them.
The SDM is not very explicit. It should have been.
>
> This reminds me: this code in extable.c needs to change.
>
> __visible bool ex_handler_fprestore(const struct exception_table_entry *fixup,
> struct pt_regs *regs, int trapnr,
> unsigned long error_code,
> unsigned long fault_addr)
> {
> regs->ip = ex_fixup_addr(fixup);
>
> WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing
> FPU registers.",
> (void *)instruction_pointer(regs));
>
> __copy_kernel_to_fpregs(&init_fpstate, -1);
>
> Now that we have supervisor states like CET, this is buggy. This
> should do something intelligent like initializing all the *user* state
> and trying again. If that succeeds, a signal should be sent rather
> than just corrupting the task. And if it fails, then perhaps some
> actual intelligence is needed. We certainly should not just disable
> CET because something is wrong with the CET MSRs.
>
Yes, but it needs more thought. Maybe a separate patch and more discussion?
Yu-cheng
next prev parent reply other threads:[~2020-09-28 19:04 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-25 14:57 [PATCH v13 0/8] Control-flow Enforcement: Indirect Branch Tracking Yu-cheng Yu
2020-09-25 14:57 ` [PATCH v13 1/8] x86/cet/ibt: Add Kconfig option for user-mode " Yu-cheng Yu
2020-09-25 14:57 ` [PATCH v13 2/8] x86/cet/ibt: User-mode Indirect Branch Tracking support Yu-cheng Yu
2020-09-25 14:57 ` [PATCH v13 3/8] x86/cet/ibt: Handle signals for Indirect Branch Tracking Yu-cheng Yu
2020-09-25 14:58 ` [PATCH v13 4/8] x86/cet/ibt: ELF header parsing " Yu-cheng Yu
2020-09-25 14:58 ` [PATCH v13 5/8] x86/cet/ibt: Update arch_prctl functions " Yu-cheng Yu
2020-09-25 14:58 ` [PATCH v13 6/8] x86/vdso/32: Add ENDBR32 to __kernel_vsyscall entry point Yu-cheng Yu
2020-09-25 14:58 ` [PATCH v13 7/8] x86/vdso: Insert endbr32/endbr64 to vDSO Yu-cheng Yu
2020-09-25 16:18 ` Andy Lutomirski
2020-09-25 16:24 ` Yu, Yu-cheng
2020-09-25 14:58 ` [PATCH v13 8/8] x86/vsyscall/64: Fixup Shadow Stack and Indirect Branch Tracking for vsyscall emulation Yu-cheng Yu
2020-09-25 16:31 ` Andy Lutomirski
2020-09-25 16:47 ` Yu, Yu-cheng
2020-09-25 16:51 ` Andy Lutomirski
2020-09-28 16:59 ` Yu-cheng Yu
2020-09-28 17:37 ` Andy Lutomirski
2020-09-28 19:04 ` Yu, Yu-cheng [this message]
2020-09-29 18:37 ` Yu, Yu-cheng
2020-09-29 19:57 ` Andy Lutomirski
2020-09-29 20:00 ` Andy Lutomirski
2020-09-30 22:33 ` Yu, Yu-cheng
2020-09-30 23:44 ` Andy Lutomirski
2020-10-01 1:00 ` H.J. Lu
2020-10-01 1:10 ` Andy Lutomirski
2020-10-01 1:21 ` H.J. Lu
2020-10-01 16:51 ` Yu, Yu-cheng
2020-10-01 17:26 ` Andy Lutomirski
2020-10-06 19:09 ` Yu, Yu-cheng
2020-10-09 17:42 ` Andy Lutomirski
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=054bd574-1566-2be4-b542-884500b7319d@intel.com \
--to=yu-cheng.yu@intel.com \
--cc=Dave.Martin@arm.com \
--cc=arnd@arndb.de \
--cc=bp@alien8.de \
--cc=bsingharora@gmail.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=esyr@redhat.com \
--cc=fweimer@redhat.com \
--cc=gorcunov@gmail.com \
--cc=hjl.tools@gmail.com \
--cc=hpa@zytor.com \
--cc=jannh@google.com \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=mike.kravetz@oracle.com \
--cc=mingo@redhat.com \
--cc=nadav.amit@gmail.com \
--cc=oleg@redhat.com \
--cc=pavel@ucw.cz \
--cc=pengfei.xu@intel.com \
--cc=peterz@infradead.org \
--cc=ravi.v.shankar@intel.com \
--cc=rdunlap@infradead.org \
--cc=tglx@linutronix.de \
--cc=vedvyas.shanbhogue@intel.com \
--cc=weijiang.yang@intel.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).