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[192.55.52.136]) by mx.google.com with ESMTPS id e6-v6si18699657pfa.217.2018.07.10.15.31.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 10 Jul 2018 15:31:17 -0700 (PDT) Received-SPF: pass (google.com: domain of yu-cheng.yu@intel.com designates 192.55.52.136 as permitted sender) client-ip=192.55.52.136; Authentication-Results: mx.google.com; spf=pass (google.com: domain of yu-cheng.yu@intel.com designates 192.55.52.136 as permitted sender) smtp.mailfrom=yu-cheng.yu@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Jul 2018 15:31:16 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,335,1526367600"; d="scan'208";a="70305437" Received: from 2b52.sc.intel.com ([143.183.136.52]) by fmsmga004.fm.intel.com with ESMTP; 10 Jul 2018 15:31:15 -0700 From: Yu-cheng Yu 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 , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , "Ravi V. Shankar" , Vedvyas Shanbhogue Cc: Yu-cheng Yu Subject: [RFC PATCH v2 19/27] x86/cet/shstk: Signal handling for shadow stack Date: Tue, 10 Jul 2018 15:26:31 -0700 Message-Id: <20180710222639.8241-20-yu-cheng.yu@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20180710222639.8241-1-yu-cheng.yu@intel.com> References: <20180710222639.8241-1-yu-cheng.yu@intel.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP When setting up a signal, the kernel creates a shadow stack restore token at the current SHSTK address and then stores the token's address in the signal frame, right after the FPU state. Before restoring a signal, the kernel verifies and then uses the restore token to set the SHSTK pointer. Signed-off-by: Yu-cheng Yu --- arch/x86/ia32/ia32_signal.c | 13 +++ arch/x86/include/asm/cet.h | 5 ++ arch/x86/include/asm/sighandling.h | 5 ++ arch/x86/include/uapi/asm/sigcontext.h | 17 ++++ arch/x86/kernel/cet.c | 115 +++++++++++++++++++++++++ arch/x86/kernel/signal.c | 96 +++++++++++++++++++++ 6 files changed, 251 insertions(+) diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 86b1341cba9a..cea28d2a946e 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -34,6 +34,7 @@ #include #include #include +#include /* * Do a signal return; undo the signal stack. @@ -108,6 +109,9 @@ static int ia32_restore_sigcontext(struct pt_regs *regs, err |= fpu__restore_sig(buf, 1); + if (!err) + err = restore_sigcontext_ext(buf); + force_iret(); return err; @@ -234,6 +238,10 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs, if (fpu->initialized) { unsigned long fx_aligned, math_size; + /* sigcontext extension */ + if (boot_cpu_has(X86_FEATURE_SHSTK)) + sp -= (sizeof(struct sc_ext) + 8); + sp = fpu__alloc_mathframe(sp, 1, &fx_aligned, &math_size); *fpstate = (struct _fpstate_32 __user *) sp; if (copy_fpstate_to_sigframe(*fpstate, (void __user *)fx_aligned, @@ -277,6 +285,8 @@ int ia32_setup_frame(int sig, struct ksignal *ksig, if (ia32_setup_sigcontext(&frame->sc, fpstate, regs, set->sig[0])) return -EFAULT; + if (setup_sigcontext_ext(ksig, fpstate)) + return -EFAULT; if (_COMPAT_NSIG_WORDS > 1) { if (__copy_to_user(frame->extramask, &set->sig[1], @@ -384,6 +394,9 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig, regs, set->sig[0]); err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); + if (!err) + err = setup_sigcontext_ext(ksig, fpstate); + if (err) return -EFAULT; diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h index ad278c520414..d9ae3d86cdd7 100644 --- a/arch/x86/include/asm/cet.h +++ b/arch/x86/include/asm/cet.h @@ -19,10 +19,15 @@ struct cet_status { int cet_setup_shstk(void); void cet_disable_shstk(void); void cet_disable_free_shstk(struct task_struct *p); +int cet_restore_signal(unsigned long ssp); +int cet_setup_signal(bool ia32, unsigned long rstor, unsigned long *new_ssp); #else static inline int cet_setup_shstk(void) { return 0; } static inline void cet_disable_shstk(void) {} static inline void cet_disable_free_shstk(struct task_struct *p) {} +static inline int cet_restore_signal(unsigned long ssp) { return 0; } +static inline int cet_setup_signal(bool ia32, unsigned long rstor, + unsigned long *new_ssp) { return 0; } #endif #endif /* __ASSEMBLY__ */ diff --git a/arch/x86/include/asm/sighandling.h b/arch/x86/include/asm/sighandling.h index bd26834724e5..23014b4082de 100644 --- a/arch/x86/include/asm/sighandling.h +++ b/arch/x86/include/asm/sighandling.h @@ -17,4 +17,9 @@ void signal_fault(struct pt_regs *regs, void __user *frame, char *where); int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate, struct pt_regs *regs, unsigned long mask); +#ifdef CONFIG_X86_64 +int setup_sigcontext_ext(struct ksignal *ksig, void __user *fpu); +int restore_sigcontext_ext(void __user *fpu); +#endif + #endif /* _ASM_X86_SIGHANDLING_H */ diff --git a/arch/x86/include/uapi/asm/sigcontext.h b/arch/x86/include/uapi/asm/sigcontext.h index 844d60eb1882..74f5ea5dcd24 100644 --- a/arch/x86/include/uapi/asm/sigcontext.h +++ b/arch/x86/include/uapi/asm/sigcontext.h @@ -196,6 +196,23 @@ struct _xstate { /* New processor state extensions go here: */ }; +#ifdef __x86_64__ +/* + * Sigcontext extension (struct sc_ext) is located after + * sigcontext->fpstate. Because currently only the shadow + * stack pointer is saved there and the shadow stack depends + * on XSAVES, we can find sc_ext from sigcontext->fpstate. + * + * The 64-bit fpstate has a size of fpu_user_xstate_size, plus + * FP_XSTATE_MAGIC2_SIZE when XSAVE* is used. The struct sc_ext + * is located at the end of sigcontext->fpstate, aligned to 8. + */ +struct sc_ext { + unsigned long total_size; + unsigned long ssp; +}; +#endif + /* * The 32-bit signal frame: */ diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c index 96bf69db7da7..4eba7790c4e4 100644 --- a/arch/x86/kernel/cet.c +++ b/arch/x86/kernel/cet.c @@ -18,6 +18,7 @@ #include #include #include +#include #define SHSTK_SIZE_64 (0x8000 * 8) #define SHSTK_SIZE_32 (0x8000 * 4) @@ -49,6 +50,69 @@ static unsigned long get_shstk_addr(void) return ptr; } +/* + * Verify the restore token at the address of 'ssp' is + * valid and then set shadow stack pointer according to the + * token. + */ +static int verify_rstor_token(bool ia32, unsigned long ssp, + unsigned long *new_ssp) +{ + unsigned long token; + + *new_ssp = 0; + + if (!IS_ALIGNED(ssp, 8)) + return -EINVAL; + + if (get_user(token, (unsigned long __user*)ssp)) + return -EFAULT; + + /* Is 64-bit mode flag correct? */ + if (ia32 && (token & 3) != 0) + return -EINVAL; + else if ((token & 3) != 1) + return -EINVAL; + + token &= ~(1UL); + + if ((!ia32 && !IS_ALIGNED(token, 8)) || !IS_ALIGNED(token, 4)) + return -EINVAL; + + if ((ALIGN_DOWN(token, 8) - 8) != ssp) + return -EINVAL; + + *new_ssp = token; + return 0; +} + +/* + * 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 *new_ssp) +{ + unsigned long addr; + + *new_ssp = 0; + + if ((!ia32 && !IS_ALIGNED(ssp, 8)) || !IS_ALIGNED(ssp, 4)) + return -EINVAL; + + addr = ALIGN_DOWN(ssp, 8) - 8; + + /* Is the token for 64-bit? */ + if (!ia32) + ssp |= 1; + + if (write_user_shstk_64(addr, ssp)) + return -EFAULT; + + *new_ssp = addr; + return 0; +} + static unsigned long shstk_mmap(unsigned long addr, unsigned long len) { struct mm_struct *mm = current->mm; @@ -126,3 +190,54 @@ void cet_disable_free_shstk(struct task_struct *tsk) tsk->thread.cet.shstk_enabled = 0; } + +int cet_restore_signal(unsigned long ssp) +{ + unsigned long new_ssp; + int err; + + if (!current->thread.cet.shstk_enabled) + return 0; + + err = verify_rstor_token(in_ia32_syscall(), ssp, &new_ssp); + + if (err) + return err; + + return set_shstk_ptr(new_ssp); +} + +/* + * Setup the shadow stack for the signal handler: first, + * create a restore token to keep track of the current ssp, + * and then the return address of the signal handler. + */ +int cet_setup_signal(bool ia32, unsigned long rstor_addr, + unsigned long *new_ssp) +{ + unsigned long ssp; + int err; + + if (!current->thread.cet.shstk_enabled) + return 0; + + ssp = get_shstk_addr(); + err = create_rstor_token(ia32, ssp, new_ssp); + + if (err) + return err; + + if (ia32) { + ssp = *new_ssp - sizeof(u32); + err = write_user_shstk_32(ssp, (unsigned int)rstor_addr); + } else { + ssp = *new_ssp - sizeof(u64); + err = write_user_shstk_64(ssp, rstor_addr); + } + + if (err) + return err; + + set_shstk_ptr(ssp); + return 0; +} diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index 92a3b312a53c..31f45d8d794a 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -46,6 +46,7 @@ #include #include +#include #define COPY(x) do { \ get_user_ex(regs->x, &sc->x); \ @@ -152,6 +153,10 @@ static int restore_sigcontext(struct pt_regs *regs, err |= fpu__restore_sig(buf, IS_ENABLED(CONFIG_X86_32)); +#ifdef CONFIG_X86_64 + err |= restore_sigcontext_ext(buf); +#endif + force_iret(); return err; @@ -266,6 +271,11 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, } if (fpu->initialized) { +#ifdef CONFIG_X86_64 + /* sigcontext extension */ + if (boot_cpu_has(X86_FEATURE_SHSTK)) + sp -= sizeof(struct sc_ext) + 8; +#endif sp = fpu__alloc_mathframe(sp, IS_ENABLED(CONFIG_X86_32), &buf_fx, &math_size); *fpstate = (void __user *)sp; @@ -493,6 +503,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig, err |= setup_sigcontext(&frame->uc.uc_mcontext, fp, regs, set->sig[0]); err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); + if (!err) + err = setup_sigcontext_ext(ksig, fp); + if (err) return -EFAULT; @@ -576,6 +589,9 @@ static int x32_setup_rt_frame(struct ksignal *ksig, regs, set->sig[0]); err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)); + if (!err) + err = setup_sigcontext_ext(ksig, fpstate); + if (err) return -EFAULT; @@ -707,6 +723,86 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs) } } +#ifdef CONFIG_X86_64 +static int copy_ext_from_user(struct sc_ext *ext, void __user *fpu) +{ + void __user *p; + + if (!fpu) + return -EINVAL; + + p = fpu + fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE; + p = (void __user *)ALIGN((unsigned long)p, 8); + + if (!access_ok(VERIFY_READ, p, sizeof(*ext))) + return -EFAULT; + + if (__copy_from_user(ext, p, sizeof(*ext))) + return -EFAULT; + + if (ext->total_size != sizeof(*ext)) + return -EINVAL; + return 0; +} + +static int copy_ext_to_user(void __user *fpu, struct sc_ext *ext) +{ + void __user *p; + + if (!fpu) + return -EINVAL; + + if (ext->total_size != sizeof(*ext)) + return -EINVAL; + + p = fpu + fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE; + p = (void __user *)ALIGN((unsigned long)p, 8); + + if (!access_ok(VERIFY_WRITE, p, sizeof(*ext))) + return -EFAULT; + + if (__copy_to_user(p, ext, sizeof(*ext))) + return -EFAULT; + + return 0; +} + +int restore_sigcontext_ext(void __user *fp) +{ + int err = 0; + + if (boot_cpu_has(X86_FEATURE_SHSTK) && fp) { + struct sc_ext ext = {0, 0}; + + err = copy_ext_from_user(&ext, fp); + + if (!err) + err = cet_restore_signal(ext.ssp); + } + + return err; +} + +int setup_sigcontext_ext(struct ksignal *ksig, void __user *fp) +{ + int err = 0; + + if (boot_cpu_has(X86_FEATURE_SHSTK) && fp) { + struct sc_ext ext; + unsigned long rstor; + + rstor = (unsigned long)ksig->ka.sa.sa_restorer; + err = cet_setup_signal(is_ia32_frame(ksig), rstor, &ext.ssp); + if (!err) { + ext.total_size = sizeof(ext); + err = copy_ext_to_user(fp, &ext); + } + } + + return err; +} +#endif + static void handle_signal(struct ksignal *ksig, struct pt_regs *regs) {