From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga05.intel.com ([192.55.52.43]:3990 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728512AbeJKWs0 (ORCPT ); Thu, 11 Oct 2018 18:48:26 -0400 From: Yu-cheng Yu Subject: [PATCH v5 21/27] x86/cet/shstk: Introduce WRUSS instruction Date: Thu, 11 Oct 2018 08:15:17 -0700 Message-ID: <20181011151523.27101-22-yu-cheng.yu@intel.com> In-Reply-To: <20181011151523.27101-1-yu-cheng.yu@intel.com> References: <20181011151523.27101-1-yu-cheng.yu@intel.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , 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 , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue Cc: Yu-cheng Yu Message-ID: <20181011151517.TKEcsf41ie7syc8qZwe_fA3qkg0cOoqXIrtWFohInOA@z> WRUSS is a new kernel-mode instruction but writes directly to user shadow stack memory. This is used to construct a return address on the shadow stack for the signal handler. This instruction can fault if the user shadow stack is invalid shadow stack memory. In that case, the kernel does a fixup. Signed-off-by: Yu-cheng Yu --- arch/x86/include/asm/special_insns.h | 32 ++++++++++++++++++++++++++++ arch/x86/mm/fault.c | 9 ++++++++ 2 files changed, 41 insertions(+) diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 317fc59b512c..37f16269747d 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -237,6 +237,38 @@ static inline void clwb(volatile void *__p) : [pax] "a" (p)); } +#ifdef CONFIG_X86_INTEL_CET +#if defined(CONFIG_IA32_EMULATION) || defined(CONFIG_X86_X32) +static inline int write_user_shstk_32(unsigned long addr, unsigned int val) +{ + asm_volatile_goto("1: wrussd %1, (%0)\n" + _ASM_EXTABLE(1b, %l[fail]) + :: "r" (addr), "r" (val) + :: fail); + return 0; +fail: + return -EPERM; +} +#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) +{ + asm_volatile_goto("1: wrussq %1, (%0)\n" + _ASM_EXTABLE(1b, %l[fail]) + :: "r" (addr), "r" (val) + :: fail); + return 0; +fail: + return -EPERM; +} +#endif /* CONFIG_X86_INTEL_CET */ + #define nop() asm volatile ("nop") diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 7c3877a982f4..b91fc008f33a 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1305,6 +1305,15 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code, error_code |= X86_PF_USER; flags |= FAULT_FLAG_USER; } else { + /* + * WRUSS is a kernel instruction and but writes + * to user shadow stack. When a fault occurs, + * both X86_PF_USER and X86_PF_SHSTK are set. + * Clear X86_PF_USER here. + */ + if ((error_code & (X86_PF_USER | X86_PF_SHSTK)) == + (X86_PF_USER | X86_PF_SHSTK)) + error_code &= ~X86_PF_USER; if (regs->flags & X86_EFLAGS_IF) local_irq_enable(); } -- 2.17.1