From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: [RFC PATCH v9 18/27] x86/cet/shstk: Introduce WRUSS instruction Date: Wed, 5 Feb 2020 10:19:26 -0800 Message-ID: <20200205181935.3712-19-yu-cheng.yu@intel.com> References: <20200205181935.3712-1-yu-cheng.yu@intel.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20200205181935.3712-1-yu-cheng.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org 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 , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit Cc: Yu-cheng Yu List-Id: linux-api@vger.kernel.org WRUSS is a new kernel-mode instruction but writes directly to user Shadow Stack (SHSTK) memory. This is used to construct a return address on SHSTK for the signal handler. This instruction can fault if the user SHSTK is not valid SHSTK memory. In that case, the kernel does a fixup. v4: - Change to asm goto. Signed-off-by: Yu-cheng Yu --- arch/x86/include/asm/special_insns.h | 32 ++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 6d37b8fcfc77..1b9b2e79c353 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -222,6 +222,38 @@ 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") -- 2.21.0