From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: [PATCH v8 21/27] x86/cet/shstk: Handle signals for shadow stack Date: Tue, 13 Aug 2019 13:52:19 -0700 Message-ID: <20190813205225.12032-22-yu-cheng.yu@intel.com> References: <20190813205225.12032-1-yu-cheng.yu@intel.com> Return-path: In-Reply-To: <20190813205225.12032-1-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 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 | 8 ++ arch/x86/include/asm/cet.h | 7 ++ arch/x86/include/asm/fpu/internal.h | 2 + arch/x86/include/asm/fpu/signal.h | 2 + arch/x86/include/uapi/asm/sigcontext.h | 15 +++ arch/x86/kernel/cet.c | 141 +++++++++++++++++++++++++ arch/x86/kernel/fpu/signal.c | 67 ++++++++++++ arch/x86/kernel/signal.c | 8 ++ 8 files changed, 250 insertions(+) diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 1cee10091b9f..73a0c1dc3123 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. @@ -235,6 +236,7 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs, ksig->ka.sa.sa_restorer) sp = (unsigned long) ksig->ka.sa.sa_restorer; + sp = fpu__alloc_sigcontext_ext(sp); 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, @@ -295,6 +297,9 @@ int ia32_setup_frame(int sig, struct ksignal *ksig, restorer = &frame->retcode; } + if (setup_fpu_system_states(1, (unsigned long)restorer, fpstate)) + return -EFAULT; + put_user_try { put_user_ex(ptr_to_compat(restorer), &frame->pretcode); @@ -384,6 +389,9 @@ 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_fpu_system_states(1, (unsigned long)restorer, fpstate); + if (err) return -EFAULT; diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h index c952a2ec65fe..422ccb8adbb7 100644 --- a/arch/x86/include/asm/cet.h +++ b/arch/x86/include/asm/cet.h @@ -6,6 +6,8 @@ #include struct task_struct; +struct sc_ext; + /* * Per-thread CET status */ @@ -19,10 +21,15 @@ 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(bool ia32, struct sc_ext *sc); +int cet_setup_signal(bool ia32, unsigned long rstor, struct sc_ext *sc); #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(bool ia32, struct sc_ext *sc) { return -EINVAL; } +static inline int cet_setup_signal(bool ia32, unsigned long rstor, + struct sc_ext *sc) { return -EINVAL; } #endif #define cpu_x86_cet_enabled() \ diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h index 2ca5c36a77d5..8a40d676c448 100644 --- a/arch/x86/include/asm/fpu/internal.h +++ b/arch/x86/include/asm/fpu/internal.h @@ -472,6 +472,8 @@ static inline void copy_kernel_to_fpregs(union fpregs_state *fpstate) __copy_kernel_to_fpregs(fpstate, -1); } +extern int setup_fpu_system_states(int is_ia32, unsigned long restorer, + void __user *fp); extern int copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size); /* diff --git a/arch/x86/include/asm/fpu/signal.h b/arch/x86/include/asm/fpu/signal.h index 7fb516b6893a..630a658aeea3 100644 --- a/arch/x86/include/asm/fpu/signal.h +++ b/arch/x86/include/asm/fpu/signal.h @@ -25,6 +25,8 @@ extern void convert_from_fxsr(struct user_i387_ia32_struct *env, extern void convert_to_fxsr(struct fxregs_state *fxsave, const struct user_i387_ia32_struct *env); +unsigned long fpu__alloc_sigcontext_ext(unsigned long sp); + unsigned long fpu__alloc_mathframe(unsigned long sp, int ia32_frame, unsigned long *buf_fx, unsigned long *size); 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 5e7af0cc75f9..f1cc8f4c57b8 100644 --- a/arch/x86/kernel/cet.c +++ b/arch/x86/kernel/cet.c @@ -19,6 +19,8 @@ #include #include #include +#include +#include static int set_shstk_ptr(unsigned long addr) { @@ -51,6 +53,80 @@ 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_64(token)) + return -EINVAL; + else if (ia32 && !IS_TOKEN_32(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; @@ -114,3 +190,68 @@ void cet_disable_free_shstk(struct task_struct *tsk) tsk->thread.cet.shstk_enabled = 0; } + +/* + * Called from __fpu__restore_sig() under the protection + * of fpregs_lock(). + */ +int cet_restore_signal(bool ia32, struct sc_ext *sc_ext) +{ + unsigned long new_ssp = 0; + u64 msr_ia32_u_cet = 0; + int err; + + if (current->thread.cet.shstk_enabled) { + err = verify_rstor_token(ia32, sc_ext->ssp, &new_ssp); + if (err) + return err; + + msr_ia32_u_cet |= MSR_IA32_CET_SHSTK_EN; + } + + wrmsrl(MSR_IA32_PL3_SSP, new_ssp); + wrmsrl(MSR_IA32_U_CET, msr_ia32_u_cet); + return 0; +} + +/* + * 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, struct sc_ext *sc_ext) +{ + unsigned long ssp = 0, new_ssp = 0; + u64 msr_ia32_u_cet = 0; + int err; + + msr_ia32_u_cet = 0; + ssp = 0; + + if (current->thread.cet.shstk_enabled) { + 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; + + msr_ia32_u_cet |= MSR_IA32_CET_SHSTK_EN; + sc_ext->ssp = new_ssp; + } + + modify_fpu_regs_begin(); + wrmsrl(MSR_IA32_PL3_SSP, ssp); + wrmsrl(MSR_IA32_U_CET, msr_ia32_u_cet); + modify_fpu_regs_end(); + return 0; +} diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index 4ecf1764a971..2673a2567174 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -52,6 +52,58 @@ static inline int check_for_xstate(struct fxregs_state __user *buf, return 0; } +int setup_fpu_system_states(int is_ia32, unsigned long restorer, + void __user *fp) +{ + int err = 0; + +#ifdef CONFIG_X86_64 + if (cpu_x86_cet_enabled() && fp) { + struct sc_ext ext = {0, 0}; + + err = cet_setup_signal(is_ia32, restorer, &ext); + if (!err) { + void __user *p; + + ext.total_size = sizeof(ext); + + p = fp + 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; + } + } +#endif + + return err; +} + +static int restore_fpu_system_states(int is_ia32, void __user *fp) +{ + int err = 0; + +#ifdef CONFIG_X86_64 + if (cpu_x86_cet_enabled() && fp) { + struct sc_ext ext = {0, 0}; + void __user *p; + + p = fp + 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 -EFAULT; + + err = cet_restore_signal(is_ia32, &ext); + } +#endif + + return err; +} + /* * Signal frame handlers. */ @@ -347,6 +399,10 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) pagefault_disable(); ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only); pagefault_enable(); + + if (!ret) + ret = restore_fpu_system_states(0, buf); + if (!ret) { fpregs_mark_activate(); fpregs_unlock(); @@ -433,6 +489,17 @@ int fpu__restore_sig(void __user *buf, int ia32_frame) return __fpu__restore_sig(buf, buf_fx, size); } +unsigned long fpu__alloc_sigcontext_ext(unsigned long sp) +{ + /* + * sigcontext_ext is at: fpu + fpu_user_xstate_size + + * FP_XSTATE_MAGIC2_SIZE, then aligned to 8. + */ + if (cpu_x86_cet_enabled()) + sp -= (sizeof(struct sc_ext) + 8); + return sp; +} + unsigned long fpu__alloc_mathframe(unsigned long sp, int ia32_frame, unsigned long *buf_fx, unsigned long *size) diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index ce9421ec285f..92a2c2b2dcd0 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); \ @@ -264,6 +265,7 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, sp = (unsigned long) ka->sa.sa_restorer; } + sp = fpu__alloc_sigcontext_ext(sp); sp = fpu__alloc_mathframe(sp, IS_ENABLED(CONFIG_X86_32), &buf_fx, &math_size); *fpstate = (void __user *)sp; @@ -493,6 +495,9 @@ 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_fpu_system_states(0, (unsigned long)ksig->ka.sa.sa_restorer, fp); + if (err) return -EFAULT; @@ -579,6 +584,9 @@ 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_fpu_system_states(0, (unsigned long)ksig->ka.sa.sa_restorer, fpstate); + if (err) return -EFAULT; -- 2.17.1