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Date: Tue, 6 Apr 2021 15:49:30 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc: X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>,
linux-arch <linux-arch@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>,
Andy Lutomirski <luto@...nel.org>,
Balbir Singh <bsingharora@...il.com>,
Borislav Petkov <bp@...en8.de>,
Cyrill Gorcunov <gorcunov@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Eugene Syromiatnikov <esyr@...hat.com>,
Florian Weimer <fweimer@...hat.com>,
"H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Mike Kravetz <mike.kravetz@...cle.com>,
Nadav Amit <nadav.amit@...il.com>,
Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
Peter Zijlstra <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
Dave Martin <Dave.Martin@....com>,
Weijiang Yang <weijiang.yang@...el.com>,
Pengfei Xu <pengfei.xu@...el.com>,
Haitao Huang <haitao.huang@...el.com>
Subject: Re: [PATCH v24 24/30] x86/cet/shstk: Introduce shadow stack token
setup/verify routines
On Thu, Apr 1, 2021 at 3:12 PM Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
>
> A shadow stack restore token marks a restore point of the shadow stack, and
> the address in a token must point directly above the token, which is within
> the same shadow stack. This is distinctively different from other pointers
> on the shadow stack, since those pointers point to executable code area.
>
> The restore token can be used as an extra protection for signal handling.
> To deliver a signal, create a shadow stack restore token and put the token
> and the signal restorer address on the shadow stack. In sigreturn, verify
> the token and restore from it the shadow stack pointer.
>
> Introduce token setup and verify routines. Also introduce WRUSS, which is
> a kernel-mode instruction but writes directly to user shadow stack. It is
> used to construct user signal stack as described above.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
> arch/x86/include/asm/cet.h | 9 ++
> arch/x86/include/asm/special_insns.h | 32 +++++++
> arch/x86/kernel/shstk.c | 126 +++++++++++++++++++++++++++
> 3 files changed, 167 insertions(+)
>
> diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
> index 8b83ded577cc..ef6155213b7e 100644
> --- a/arch/x86/include/asm/cet.h
> +++ b/arch/x86/include/asm/cet.h
> @@ -20,6 +20,10 @@ int shstk_setup_thread(struct task_struct *p, unsigned long clone_flags,
> unsigned long stack_size);
> void shstk_free(struct task_struct *p);
> void shstk_disable(void);
> +int shstk_setup_rstor_token(bool ia32, unsigned long rstor,
> + unsigned long *token_addr, unsigned long *new_ssp);
> +int shstk_check_rstor_token(bool ia32, unsigned long token_addr,
> + unsigned long *new_ssp);
> #else
> static inline int shstk_setup(void) { return 0; }
> static inline int shstk_setup_thread(struct task_struct *p,
> @@ -27,6 +31,11 @@ static inline int shstk_setup_thread(struct task_struct *p,
> unsigned long stack_size) { return 0; }
> static inline void shstk_free(struct task_struct *p) {}
> static inline void shstk_disable(void) {}
> +static inline int shstk_setup_rstor_token(bool ia32, unsigned long rstor,
> + unsigned long *token_addr,
> + unsigned long *new_ssp) { return 0; }
> +static inline int shstk_check_rstor_token(bool ia32, unsigned long token_addr,
> + unsigned long *new_ssp) { return 0; }
> #endif
>
> #endif /* __ASSEMBLY__ */
> diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
> index 1d3cbaef4bb7..c41c371f6c7d 100644
> --- a/arch/x86/include/asm/special_insns.h
> +++ b/arch/x86/include/asm/special_insns.h
> @@ -234,6 +234,38 @@ static inline void clwb(volatile void *__p)
> : [pax] "a" (p));
> }
>
> +#ifdef CONFIG_X86_SHADOW_STACK
> +#if defined(CONFIG_IA32_EMULATION) || defined(CONFIG_X86_X32)
> +static inline int write_user_shstk_32(unsigned long addr, unsigned int val)
u32 __user *addr?
> +{
> + asm_volatile_goto("1: wrussd %1, (%0)\n"
> + _ASM_EXTABLE(1b, %l[fail])
> + :: "r" (addr), "r" (val)
> + :: fail);
> + return 0;
> +fail:
> + return -EPERM;
-EFAULT?
> +}
> +#else
> +static inline int write_user_shstk_32(unsigned long addr, unsigned int val)
> +{
> + WARN_ONCE(1, "%s used but not supported.\n", __func__);
> + return -EFAULT;
> +}
> +#endif
> +
> +static inline int write_user_shstk_64(unsigned long addr, unsigned long val)
u64 __user *addr, perhaps?
> +{
> + asm_volatile_goto("1: wrussq %1, (%0)\n"
> + _ASM_EXTABLE(1b, %l[fail])
> + :: "r" (addr), "r" (val)
Can you use the modern [addr] "r" (addr) syntax?
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