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 S1728570AbeJKWs0 (ORCPT ); Thu, 11 Oct 2018 18:48:26 -0400 From: Yu-cheng Yu Subject: [PATCH v5 22/27] x86/cet/shstk: Signal handling for shadow stack Date: Thu, 11 Oct 2018 08:15:18 -0700 Message-ID: <20181011151523.27101-23-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: <20181011151518.NkrhPQwF6hWDseQpdkldJnLagxwwgAGesYqiwrewO9M@z> 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 | 15 +++ arch/x86/kernel/cet.c | 126 +++++++++++++++++++++++++ arch/x86/kernel/signal.c | 97 +++++++++++++++++++ 6 files changed, 261 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 c952a2ec65fe..3af544aed800 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 -EINVAL; } 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 -EINVAL; } +static inline int cet_setup_signal(bool ia32, unsigned long rstor, + unsigned long *new_ssp) { return -EINVAL; } #endif #define cpu_x86_cet_enabled() \ 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..e3b08d1c0d3b 100644 --- a/arch/x86/include/uapi/asm/sigcontext.h +++ b/arch/x86/include/uapi/asm/sigcontext.h @@ -196,6 +196,21 @@ struct _xstate { /* New processor state extensions go here: */ }; +/* + * 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; +}; + /* * The 32-bit signal frame: */ diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c index ec256ae27a31..2000e5e87f8f 100644 --- a/arch/x86/kernel/cet.c +++ b/arch/x86/kernel/cet.c @@ -18,6 +18,7 @@ #include #include #include +#include static int set_shstk_ptr(unsigned long addr) { @@ -46,6 +47,80 @@ static unsigned long get_shstk_addr(void) return ptr; } +#define TOKEN_MODE_MASK 3UL +#define TOKEN_MODE_64 1UL +#define IS_TOKEN_64(token) ((token & TOKEN_MODE_MASK) == TOKEN_MODE_64) +#define IS_TOKEN_32(token) ((token & TOKEN_MODE_MASK) == 0) + +/* + * 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 && !IS_TOKEN_32(token)) + return -EINVAL; + else if (!IS_TOKEN_64(token)) + return -EINVAL; + + token &= ~TOKEN_MODE_MASK; + + /* + * Restore address properly aligned? + */ + if ((!ia32 && !IS_ALIGNED(token, 8)) || !IS_ALIGNED(token, 4)) + return -EINVAL; + + /* + * Token was placed properly? + */ + 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 |= TOKEN_MODE_64; + + if (write_user_shstk_64(addr, ssp)) + return -EFAULT; + + *new_ssp = addr; + return 0; +} + int cet_setup_shstk(void) { unsigned long addr, size; @@ -107,3 +182,54 @@ 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..a0cee6ba99a0 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; @@ -237,6 +242,17 @@ static unsigned long align_sigframe(unsigned long sp) return sp; } +static unsigned long alloc_sigcontext_ext(unsigned long sp) +{ + /* + * sigcontext_ext is at: fpu + fpu_user_xstate_size + + * FP_XSTATE_MAGIC2_SIZE, then aligned to 8. + */ + if (boot_cpu_has(X86_FEATURE_SHSTK)) + sp -= (sizeof(struct sc_ext) + 8); + return sp; +} + static void __user * get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, void __user **fpstate) @@ -266,6 +282,7 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, } if (fpu->initialized) { + sp = alloc_sigcontext_ext(sp); sp = fpu__alloc_mathframe(sp, IS_ENABLED(CONFIG_X86_32), &buf_fx, &math_size); *fpstate = (void __user *)sp; @@ -493,6 +510,9 @@ 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 +596,9 @@ 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 +730,80 @@ 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 (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 (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