From: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
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 v26 24/30] x86/cet/shstk: Introduce shadow stack token setup/verify routines
Date: Mon, 17 May 2021 13:55:01 -0700 [thread overview]
Message-ID: <e225e357-a1d5-9596-8900-79e6b94cf924@intel.com> (raw)
In-Reply-To: <YKIfIEyW+sR+bDCk@zn.tnic>
On 5/17/2021 12:45 AM, Borislav Petkov wrote:
> On Tue, Apr 27, 2021 at 01:43:09PM -0700, Yu-cheng Yu wrote:
>> +static inline int write_user_shstk_32(u32 __user *addr, u32 val)
>> +{
>> + WARN_ONCE(1, "%s used but not supported.\n", __func__);
>> + return -EFAULT;
>> +}
>> +#endif
>
> What is that supposed to catch? Any concrete (mis-)use cases?
>
If 32-bit apps are not supported, there should be no need of 32-bit
shadow stack write, otherwise there is a bug.
[...]
>> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
>> index d387df84b7f1..48a0c87414ef 100644
>> --- a/arch/x86/kernel/shstk.c
>> +++ b/arch/x86/kernel/shstk.c
>> @@ -20,6 +20,7 @@
>> #include <asm/fpu/xstate.h>
>> #include <asm/fpu/types.h>
>> #include <asm/cet.h>
>> +#include <asm/special_insns.h>
>>
>> static void start_update_msrs(void)
>> {
>> @@ -176,3 +177,128 @@ void shstk_disable(void)
>>
>> shstk_free(current);
>> }
>> +
>> +static unsigned long _get_user_shstk_addr(void)
>
> What's the "_" prefix in the name supposed to denote?
>
> Ditto for the other functions with "_" prefix you're adding.
>
These are static functions. I thought that would make the static scope
clear. I can remove "_".
>> +{
>> + struct fpu *fpu = ¤t->thread.fpu;
>> + unsigned long ssp = 0;
>> +
>> + fpregs_lock();
>> +
>> + if (fpregs_state_valid(fpu, smp_processor_id())) {
>> + rdmsrl(MSR_IA32_PL3_SSP, ssp);
>> + } else {
>> + struct cet_user_state *p;
>> +
>> + p = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER);
>> + if (p)
>> + ssp = p->user_ssp;
>> + }
>> +
>> + fpregs_unlock();
>
> <---- newline here.
>
>> + return ssp;
>> +}
>> +
>> +#define TOKEN_MODE_MASK 3UL
>> +#define TOKEN_MODE_64 1UL
>> +#define IS_TOKEN_64(token) (((token) & TOKEN_MODE_MASK) == TOKEN_MODE_64)
>> +#define IS_TOKEN_32(token) (((token) & TOKEN_MODE_MASK) == 0)
>
> Why do you have to look at the second, busy bit, too in order to
> determine the mode?
>
If the busy bit is set, it is only for SAVEPREVSSP, and invalid as a
normal restore token.
> Also, you don't need most of those defines - see below.
>
>> +/*
>> + * Create a restore token on the shadow stack. A token is always 8-byte
>> + * and aligned to 8.
>> + */
>> +static int _create_rstor_token(bool ia32, unsigned long ssp,
>> + unsigned long *token_addr)
>> +{
>> + unsigned long addr;
>> +
>> + *token_addr = 0;
>
> What for? Callers should check this function's retval and then interpret
> the validity of token_addr and it should not unconditionally write into
> it.
>
Ok.
>> +
>> + if ((!ia32 && !IS_ALIGNED(ssp, 8)) || !IS_ALIGNED(ssp, 4))
>
> Flip this logic:
>
> if ((ia32 && !IS_ALIGNED(ssp, 4)) || !IS_ALIGNED(ssp, 8))
>
>> + return -EINVAL;
>> +
>> + addr = ALIGN_DOWN(ssp, 8) - 8;
>
> Yah, so this is weird. Why does the restore token need to be at -8
> instead on the shadow stack address itself?
With the lower two bits masked out, the restore token must point
directly above itself.
>
> Looking at
>
> Figure 18-2. RSTORSSP to Switch to New Shadow Stack
> Figure 18-3. SAVEPREVSSP to Save a Restore Point
>
> in the SDM, it looks like unnecessarily more complex than it should be.
> But maybe there's some magic I'm missing.
>
>> +
>> + /* Is the token for 64-bit? */
>> + if (!ia32)
>> + ssp |= TOKEN_MODE_64;
>
> |= BIT(0);
>
Ok, then, we don't use #define's. I will put in comments about what it
is doing, and fix the rest.
Thanks,
Yu-cheng
next prev parent reply other threads:[~2021-05-17 20:55 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 20:42 [PATCH v26 00/30] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 01/30] Documentation/x86: Add CET description Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 02/30] x86/cet/shstk: Add Kconfig option for Shadow Stack Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 03/30] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 04/30] x86/cpufeatures: Introduce CPU setup and option parsing for CET Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 05/30] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 06/30] x86/cet: Add control-protection fault handler Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 07/30] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 08/30] x86/mm: Move pmd_write(), pud_write() up in the file Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 09/30] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 10/30] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 11/30] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 12/30] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 13/30] mm: Introduce VM_SHADOW_STACK for shadow stack memory Yu-cheng Yu
2021-04-27 20:42 ` [PATCH v26 14/30] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 15/30] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 16/30] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 17/30] mm: Add guard pages around a shadow stack Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 18/30] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 19/30] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 20/30] mm/mprotect: Exclude shadow stack from preserve_write Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 21/30] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 22/30] x86/cet/shstk: Add user-mode shadow stack support Yu-cheng Yu
2021-04-28 17:52 ` Borislav Petkov
2021-04-28 18:39 ` Yu, Yu-cheng
2021-04-29 9:12 ` Borislav Petkov
2021-04-29 16:17 ` Yu, Yu-cheng
2021-04-29 16:45 ` Borislav Petkov
2021-04-27 20:43 ` [PATCH v26 23/30] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2021-05-10 14:15 ` Borislav Petkov
2021-05-10 22:57 ` Yu, Yu-cheng
2021-05-11 17:09 ` Borislav Petkov
2021-05-12 8:12 ` David Laight
2021-05-11 18:35 ` Yu, Yu-cheng
2021-05-12 15:56 ` Borislav Petkov
2021-04-27 20:43 ` [PATCH v26 24/30] x86/cet/shstk: Introduce shadow stack token setup/verify routines Yu-cheng Yu
2021-05-17 7:45 ` Borislav Petkov
2021-05-17 20:55 ` Yu, Yu-cheng [this message]
2021-05-18 0:14 ` Eugene Syromiatnikov
2021-05-18 17:58 ` Borislav Petkov
2021-05-18 19:45 ` Yu, Yu-cheng
2021-05-18 18:05 ` Yu, Yu-cheng
2021-05-18 5:56 ` Borislav Petkov
2021-05-21 16:17 ` Yu, Yu-cheng
2021-05-21 18:40 ` Borislav Petkov
2021-04-27 20:43 ` [PATCH v26 25/30] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2021-04-28 23:03 ` extending ucontext (Re: [PATCH v26 25/30] x86/cet/shstk: Handle signals for shadow stack) Andy Lutomirski
2021-04-28 23:20 ` Yu, Yu-cheng
2021-04-29 7:28 ` Cyrill Gorcunov
2021-04-29 14:44 ` Andy Lutomirski
2021-04-29 15:35 ` Cyrill Gorcunov
2021-04-30 6:45 ` Florian Weimer
2021-04-30 17:00 ` Yu, Yu-cheng
2021-04-30 17:47 ` Andy Lutomirski
2021-04-30 18:32 ` Yu, Yu-cheng
2021-05-04 20:49 ` Yu, Yu-cheng
2021-05-06 22:05 ` Yu, Yu-cheng
2021-05-06 23:31 ` Andy Lutomirski
2021-05-02 23:23 ` Andy Lutomirski
2021-05-03 6:03 ` H. Peter Anvin
2021-05-03 15:13 ` Yu, Yu-cheng
2021-05-03 15:29 ` Andy Lutomirski
2021-05-03 20:25 ` Yu, Yu-cheng
2021-04-27 20:43 ` [PATCH v26 26/30] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2021-05-19 18:10 ` Borislav Petkov
2021-05-19 22:14 ` Yu, Yu-cheng
2021-05-20 9:26 ` Borislav Petkov
2021-05-20 17:18 ` Yu, Yu-cheng
2021-05-20 17:35 ` Borislav Petkov
2021-05-20 17:51 ` Yu, Yu-cheng
2021-05-20 17:38 ` Matthew Wilcox
2021-05-20 17:52 ` Yu, Yu-cheng
2021-05-20 21:06 ` Yu, Yu-cheng
2021-04-27 20:43 ` [PATCH v26 27/30] x86/cet/shstk: Add arch_prctl functions for shadow stack Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 28/30] mm: Move arch_calc_vm_prot_bits() to arch/x86/include/asm/mman.h Yu-cheng Yu
2021-04-27 20:43 ` [PATCH v26 29/30] mm: Update arch_validate_flags() to test vma anonymous Yu-cheng Yu
2021-05-11 11:35 ` Kirill A. Shutemov
2021-04-27 20:43 ` [PATCH v26 30/30] mm: Introduce PROT_SHADOW_STACK for shadow stack Yu-cheng Yu
2021-05-11 11:48 ` Kirill A. Shutemov
2021-05-11 14:44 ` Yu, Yu-cheng
2021-04-29 17:13 ` [PATCH v26 00/30] Control-flow Enforcement: Shadow Stack Borislav Petkov
2021-04-29 17:32 ` Yu, Yu-cheng
2021-04-29 17:49 ` Borislav Petkov
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