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>,
Haitao Huang <haitao.huang@intel.com>
Subject: Re: [PATCH v24 25/30] x86/cet/shstk: Handle signals for shadow stack
Date: Wed, 7 Apr 2021 12:36:04 -0700 [thread overview]
Message-ID: <76743437-24b3-7c33-2570-6100c8811165@intel.com> (raw)
In-Reply-To: <CALCETrWa+gjf2c2WDVxk23xd11kTnrUmiqrMsOVXOKPL4Eg-JA@mail.gmail.com>
On 4/6/2021 3:50 PM, Andy Lutomirski wrote:
> On Thu, Apr 1, 2021 at 3:11 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>>
>> When shadow stack is enabled, a task's shadow stack states must be saved
>> along with the signal context and later restored in sigreturn. However,
>> currently there is no systematic facility for extending a signal context.
>>
>> Introduce a signal context extension struct 'sc_ext', which is used to save
>> shadow stack restore token address and WAIT_ENDBR status[1]. The extension
>> is located above the fpu states, plus alignment.
>>
>> Introduce routines for the allocation, save, and restore for sc_ext:
>> - fpu__alloc_sigcontext_ext(),
>> - save_extra_state_to_sigframe(),
>> - get_extra_state_from_sigframe(),
>> - restore_extra_state().
>>
>> [1] WAIT_ENDBR will be introduced later in the Indirect Branch Tracking
>> series, but add that into sc_ext now to keep the struct stable in case
>> the IBT series is applied later.
>
> Please don't. Instead, please figure out how that structure gets
> extended for real, and organize your patches to demonstrate that the
> extension works.
>
>>
>> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> ---
>> v24:
>> - Split out shadow stack token routines to a separate patch.
>> - Put signal frame save/restore routines to fpu/signal.c and re-name accordingly.
>>
>> arch/x86/ia32/ia32_signal.c | 16 +++
>> arch/x86/include/asm/cet.h | 2 +
>> arch/x86/include/asm/fpu/internal.h | 2 +
>> arch/x86/include/uapi/asm/sigcontext.h | 9 ++
>> arch/x86/kernel/fpu/signal.c | 143 +++++++++++++++++++++++++
>> arch/x86/kernel/signal.c | 9 ++
>> 6 files changed, 181 insertions(+)
>>
[...]
>> diff --git a/arch/x86/include/uapi/asm/sigcontext.h b/arch/x86/include/uapi/asm/sigcontext.h
>> index 844d60eb1882..cf2d55db3be4 100644
>> --- a/arch/x86/include/uapi/asm/sigcontext.h
>> +++ b/arch/x86/include/uapi/asm/sigcontext.h
>> @@ -196,6 +196,15 @@ struct _xstate {
>> /* New processor state extensions go here: */
>> };
>>
>> +/*
>> + * Located at the end of sigcontext->fpstate, aligned to 8.
>> + */
>> +struct sc_ext {
>> + unsigned long total_size;
>> + unsigned long ssp;
>> + unsigned long wait_endbr;
>> +};
>
> We need some proper documentation and an extensibility story for this.
> This won't be the last time we extend the signal state. Keep in mind
> that the FPU state is very likely to become genuinely variable sized
> due to AVX-512 and AMX.
>
Right now, on the signal stack, we have:
- siginfo, ucontext,
- fpu states (xsave state),
We might not want to change ucontext. The concern is breaking existing
app's.
Fpu states are all user states (vs. ssp, wait_endbr are supervisor
states). Therefore, we cannot put ssp and wait_endbr in fpu states.
Fpu states can grow to whatever size (AVX-512 etc.), the extension is
always above it if the user stack has room. If the user stack does not
have enough room, fpu__aloc_mathframe() fails.
The struct sc_ext has a simple 'total_size' field for error checking.
To extend it, newer fields are always added to the end and total_size
keeps track of it. I will put more comments about this.
> We also have the ability to extend ucontext, I believe, and I'd like
> some analysis of why we want to put ssp and wait_endbr into the FPU
> context instead of the ucontext.
>
[...]
>> diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
>> index a4ec65317a7f..2e56f2fe8be0 100644
>> --- a/arch/x86/kernel/fpu/signal.c
>> +++ b/arch/x86/kernel/fpu/signal.c
[...]
>> +
>> +/*
>> + * Called from __fpu__restore_sig() and XSAVES buffer is protected by
>> + * set_thread_flag(TIF_NEED_FPU_LOAD) in the slow path.
>> + */
>> +void restore_extra_state(struct sc_ext *sc_ext)
>> +{
>> +#ifdef CONFIG_X86_CET
>> + struct cet_status *cet = ¤t->thread.cet;
>> + struct cet_user_state *cet_user_state;
>> + u64 msr_val = 0;
>> +
>> + if (!cpu_feature_enabled(X86_FEATURE_CET))
>> + return;
>> +
>> + cet_user_state = get_xsave_addr(¤t->thread.fpu.state.xsave,
>> + XFEATURE_CET_USER);
>> + if (!cet_user_state)
>> + return;
>> +
>> + if (cet->shstk_size) {
>
> Is fpregs_lock() needed?
This path is already protected.
>
>> + if (test_thread_flag(TIF_NEED_FPU_LOAD))
>> + cet_user_state->user_ssp = sc_ext->ssp;
>> + else
>> + wrmsrl(MSR_IA32_PL3_SSP, sc_ext->ssp);
>
> wrmsrl_safe() please.
>
>> +
>> + msr_val |= CET_SHSTK_EN;
>> + }
>> +
>> + if (test_thread_flag(TIF_NEED_FPU_LOAD))
>> + cet_user_state->user_cet = msr_val;
>> + else
>> + wrmsrl(MSR_IA32_U_CET, msr_val);
>> +#endif
>
> I don't understand. Why are you recomputing MSR_IA32_U_CET here?
>
> As another general complaint about this patch set, there's
> cet->shstk_size and there's MSR_IA32_U_CET (and its copy in the fpu
> state), and they seem to be used somewhat interchangably. Why are
> both needed? Could there be some new helpers to help manage them all
> in a unified way?
>
Indeed, shadow stack/IBT states are cached in the thread header. Their
MSRs and XSAVES states are accessed only when necessary. The signal
restore path has been optimized in the past and I hope not to put in
code that negates past work.
I agree with your other comments for the patch and will update in the
next revision.
Thanks,
Yu-cheng
next prev parent reply other threads:[~2021-04-07 19:36 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 22:10 [PATCH v24 00/30] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 01/30] Documentation/x86: Add CET description Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 02/30] x86/cet/shstk: Add Kconfig option for Shadow Stack Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 03/30] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 04/30] x86/cpufeatures: Introduce X86_FEATURE_CET and setup functions Yu-cheng Yu
2021-04-09 10:12 ` Borislav Petkov
2021-04-09 15:52 ` Yu, Yu-cheng
2021-04-09 17:14 ` Borislav Petkov
2021-04-09 23:14 ` Yu, Yu-cheng
2021-04-10 9:29 ` Borislav Petkov
2021-04-01 22:10 ` [PATCH v24 05/30] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 06/30] x86/cet: Add control-protection fault handler Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 07/30] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 08/30] x86/mm: Move pmd_write(), pud_write() up in the file Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 09/30] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 10/30] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 11/30] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 12/30] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Yu-cheng Yu
2021-04-09 15:07 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 13/30] mm: Introduce VM_SHADOW_STACK for shadow stack memory Yu-cheng Yu
2021-04-09 15:10 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 14/30] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2021-04-09 15:12 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 15/30] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2021-04-09 15:16 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 16/30] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2021-04-09 15:20 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 17/30] mm: Add guard pages around a shadow stack Yu-cheng Yu
2021-04-09 15:22 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 18/30] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2021-04-09 15:25 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 19/30] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2021-04-09 15:31 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 20/30] mm/mprotect: Exclude shadow stack from preserve_write Yu-cheng Yu
2021-04-09 15:34 ` Kirill A. Shutemov
2021-04-01 22:10 ` [PATCH v24 21/30] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 22/30] x86/cet/shstk: Add user-mode shadow stack support Yu-cheng Yu
2021-04-09 15:57 ` Kirill A. Shutemov
2021-04-09 23:47 ` Yu, Yu-cheng
2021-04-01 22:10 ` [PATCH v24 23/30] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2021-04-01 22:10 ` [PATCH v24 24/30] x86/cet/shstk: Introduce shadow stack token setup/verify routines Yu-cheng Yu
2021-04-06 22:49 ` Andy Lutomirski
2021-04-01 22:10 ` [PATCH v24 25/30] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2021-04-06 22:50 ` Andy Lutomirski
2021-04-07 19:36 ` Yu, Yu-cheng [this message]
2021-04-01 22:11 ` [PATCH v24 26/30] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2021-04-01 22:11 ` [PATCH v24 27/30] x86/cet/shstk: Add arch_prctl functions for shadow stack Yu-cheng Yu
2021-04-01 22:11 ` [PATCH v24 28/30] mm: Move arch_calc_vm_prot_bits() to arch/x86/include/asm/mman.h Yu-cheng Yu
2021-04-01 22:11 ` [PATCH v24 29/30] mm: Update arch_validate_flags() to include vma anonymous Yu-cheng Yu
2021-04-01 22:11 ` [PATCH v24 30/30] mm: Introduce PROT_SHSTK for shadow stack Yu-cheng Yu
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