From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eugene Syromiatnikov Subject: Re: [RFC PATCH v4 20/27] x86/cet/shstk: Signal handling for shadow stack Date: Wed, 3 Oct 2018 16:36:10 +0200 Message-ID: <20181003143610.GC22724@asgard.redhat.com> References: <20180921150351.20898-1-yu-cheng.yu@intel.com> <20180921150351.20898-21-yu-cheng.yu@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180921150351.20898-21-yu-cheng.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Yu-cheng Yu Cc: 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 List-Id: linux-arch.vger.kernel.org On Fri, Sep 21, 2018 at 08:03:44AM -0700, Yu-cheng Yu wrote: > 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. > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c > index ec256ae27a31..5cc4be6e0982 100644 > --- a/arch/x86/kernel/cet.c > +++ b/arch/x86/kernel/cet.c > @@ -46,6 +47,69 @@ 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; It is probably worth adding constant names for these flags, example, there's Section 2.4 in the currently available description[1], and it took some time before I decided to look into other patches and find the patch with the documentation (or finally notice section 2.7). [1] https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-enforcement-technology-preview.pdf > + 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; Maybe refactor this check into a separate function/macro? > + > + addr = ALIGN_DOWN(ssp, 8) - 8; > + > + /* Is the token for 64-bit? */ > + if (!ia32) > + ssp |= 1; Again, usage of a named constant might document it better. > + > + if (write_user_shstk_64(addr, ssp)) This function is defined in "[RFC PATCH v4 19/27] x86/cet/shstk: Introduce WRUSS instruction" > + return -EFAULT; > + > + *new_ssp = addr; > + return 0; > +} > + > int cet_setup_shstk(void) > { > unsigned long addr, size; > @@ -107,3 +171,54 @@ 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..e9a85689143f 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); That might be refactored in a separate function. Also, it looks like that possible padding for 8-byte alignment (copy_ext_{to,from}_user) is not accounted here. > *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); > + Why is this not in setup_sigcontext, for example? > 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 = {0, 0}; > + 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) > { > -- > 2.17.1 > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:56110 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726726AbeJCVYa (ORCPT ); Wed, 3 Oct 2018 17:24:30 -0400 Date: Wed, 3 Oct 2018 16:36:10 +0200 From: Eugene Syromiatnikov Subject: Re: [RFC PATCH v4 20/27] x86/cet/shstk: Signal handling for shadow stack Message-ID: <20181003143610.GC22724@asgard.redhat.com> References: <20180921150351.20898-1-yu-cheng.yu@intel.com> <20180921150351.20898-21-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180921150351.20898-21-yu-cheng.yu@intel.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Yu-cheng Yu Cc: 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 , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue Message-ID: <20181003143610.g7FmLlv8n8k0-Oo3A-QafoH-X5uWU1-Jbm9AQgkfmmk@z> On Fri, Sep 21, 2018 at 08:03:44AM -0700, Yu-cheng Yu wrote: > 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. > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c > index ec256ae27a31..5cc4be6e0982 100644 > --- a/arch/x86/kernel/cet.c > +++ b/arch/x86/kernel/cet.c > @@ -46,6 +47,69 @@ 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; It is probably worth adding constant names for these flags, example, there's Section 2.4 in the currently available description[1], and it took some time before I decided to look into other patches and find the patch with the documentation (or finally notice section 2.7). [1] https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-enforcement-technology-preview.pdf > + 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; Maybe refactor this check into a separate function/macro? > + > + addr = ALIGN_DOWN(ssp, 8) - 8; > + > + /* Is the token for 64-bit? */ > + if (!ia32) > + ssp |= 1; Again, usage of a named constant might document it better. > + > + if (write_user_shstk_64(addr, ssp)) This function is defined in "[RFC PATCH v4 19/27] x86/cet/shstk: Introduce WRUSS instruction" > + return -EFAULT; > + > + *new_ssp = addr; > + return 0; > +} > + > int cet_setup_shstk(void) > { > unsigned long addr, size; > @@ -107,3 +171,54 @@ 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..e9a85689143f 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); That might be refactored in a separate function. Also, it looks like that possible padding for 8-byte alignment (copy_ext_{to,from}_user) is not accounted here. > *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); > + Why is this not in setup_sigcontext, for example? > 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 = {0, 0}; > + 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) > { > -- > 2.17.1 >