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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 , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu , Haitao Huang Cc: Yu-cheng Yu Subject: [PATCH v27 26/31] x86/cet/shstk: Handle signals for shadow stack Date: Fri, 21 May 2021 15:12:06 -0700 Message-Id: <20210521221211.29077-27-yu-cheng.yu@intel.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20210521221211.29077-1-yu-cheng.yu@intel.com> References: <20210521221211.29077-1-yu-cheng.yu@intel.com> MIME-Version: 1.0 Authentication-Results: imf07.hostedemail.com; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=intel.com (policy=none); spf=none (imf07.hostedemail.com: domain of yu-cheng.yu@intel.com has no SPF policy when checking 134.134.136.65) smtp.mailfrom=yu-cheng.yu@intel.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D3E87A0001C1 X-Stat-Signature: uznb6a4cs8mad8hq6mfgt7z7rssa5jgu X-HE-Tag: 1621635216-347987 Content-Transfer-Encoding: quoted-printable 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: A signal handler (if not changing ucontext) returns to the restorer, and the restorer calls sigreturn. Thus, when setting up a signal frame, the kernel: - installs a shadow stack restore token pointing to the current shadow stack address, and - installs the restorer address below the restore token. In sigreturn, the restore token is verified and shadow stack pointer is restored. Signed-off-by: Yu-cheng Yu Cc: Andy Lutomirski Cc: Cyrill Gorcunov Cc: Florian Weimer Cc: H. Peter Anvin Cc: Kees Cook --- v27: - Eliminate saving shadow stack pointer to signal context. v25: - Update commit log/comments for the sc_ext struct. - Use restorer address already calculated. - Change CONFIG_X86_CET to CONFIG_X86_SHADOW_STACK. - Change X86_FEATURE_CET to X86_FEATURE_SHSTK. - Eliminate writing to MSR_IA32_U_CET for shadow stack. - Change wrmsrl() to wrmsrl_safe() and handle error. arch/x86/ia32/ia32_signal.c | 25 +++++++++++++++++----- arch/x86/include/asm/cet.h | 4 ++++ arch/x86/kernel/shstk.c | 42 +++++++++++++++++++++++++++++++++++++ arch/x86/kernel/signal.c | 13 ++++++++++++ 4 files changed, 79 insertions(+), 5 deletions(-) diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 5e3d9b7fd5fb..d7a30bc98e66 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -35,6 +35,7 @@ #include #include #include +#include =20 static inline void reload_segments(struct sigcontext_32 *sc) { @@ -113,6 +114,10 @@ COMPAT_SYSCALL_DEFINE0(sigreturn) =20 if (ia32_restore_sigcontext(regs, &frame->sc)) goto badframe; + + if (restore_signal_shadow_stack()) + goto badframe; + return regs->ax; =20 badframe: @@ -138,6 +143,9 @@ COMPAT_SYSCALL_DEFINE0(rt_sigreturn) if (ia32_restore_sigcontext(regs, &frame->uc.uc_mcontext)) goto badframe; =20 + if (restore_signal_shadow_stack()) + goto badframe; + if (compat_restore_altstack(&frame->uc.uc_stack)) goto badframe; =20 @@ -262,6 +270,9 @@ int ia32_setup_frame(int sig, struct ksignal *ksig, restorer =3D &frame->retcode; } =20 + if (setup_signal_shadow_stack(1, restorer)) + return -EFAULT; + if (!user_access_begin(frame, sizeof(*frame))) return -EFAULT; =20 @@ -319,6 +330,15 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksi= g, =20 frame =3D get_sigframe(ksig, regs, sizeof(*frame), &fp); =20 + if (ksig->ka.sa.sa_flags & SA_RESTORER) + restorer =3D ksig->ka.sa.sa_restorer; + else + restorer =3D current->mm->context.vdso + + vdso_image_32.sym___kernel_rt_sigreturn; + + if (setup_signal_shadow_stack(1, restorer)) + return -EFAULT; + if (!user_access_begin(frame, sizeof(*frame))) return -EFAULT; =20 @@ -334,11 +354,6 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksi= g, unsafe_put_user(0, &frame->uc.uc_link, Efault); unsafe_compat_save_altstack(&frame->uc.uc_stack, regs->sp, Efault); =20 - if (ksig->ka.sa.sa_flags & SA_RESTORER) - restorer =3D ksig->ka.sa.sa_restorer; - else - restorer =3D current->mm->context.vdso + - vdso_image_32.sym___kernel_rt_sigreturn; unsafe_put_user(ptr_to_compat(restorer), &frame->pretcode, Efault); =20 /* diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h index aa533700ba31..2f7940d68ce3 100644 --- a/arch/x86/include/asm/cet.h +++ b/arch/x86/include/asm/cet.h @@ -24,6 +24,8 @@ void shstk_disable(void); int shstk_setup_rstor_token(bool ia32, unsigned long restorer, unsigned long *new_ssp); int shstk_check_rstor_token(bool ia32, unsigned long *new_ssp); +int setup_signal_shadow_stack(int ia32, void __user *restorer); +int restore_signal_shadow_stack(void); #else static inline int shstk_setup(void) { return 0; } static inline int shstk_alloc_thread_stack(struct task_struct *p, @@ -35,6 +37,8 @@ static inline int shstk_setup_rstor_token(bool ia32, un= signed long restorer, unsigned long *new_ssp) { return 0; } static inline int shstk_check_rstor_token(bool ia32, unsigned long *new_ssp) { return 0; } +static inline int setup_signal_shadow_stack(int ia32, void __user *resto= rer) { return 0; } +static inline int restore_signal_shadow_stack(void) { return 0; } #endif =20 #endif /* __ASSEMBLY__ */ diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c index 61ec300c1a97..5ef5e99afd75 100644 --- a/arch/x86/kernel/shstk.c +++ b/arch/x86/kernel/shstk.c @@ -314,3 +314,45 @@ int shstk_check_rstor_token(bool proc32, unsigned lo= ng *new_ssp) =20 return 0; } + +int setup_signal_shadow_stack(int ia32, void __user *restorer) +{ + struct thread_shstk *shstk =3D ¤t->thread.shstk; + unsigned long new_ssp; + int err; + + if (!cpu_feature_enabled(X86_FEATURE_SHSTK) || !shstk->size) + return 0; + + err =3D shstk_setup_rstor_token(ia32, (unsigned long)restorer, + &new_ssp); + if (err) + return err; + + start_update_msrs(); + err =3D wrmsrl_safe(MSR_IA32_PL3_SSP, new_ssp); + end_update_msrs(); + + return err; +} + +int restore_signal_shadow_stack(void) +{ + struct thread_shstk *shstk =3D ¤t->thread.shstk; + int ia32 =3D in_ia32_syscall(); + unsigned long new_ssp; + int err; + + if (!cpu_feature_enabled(X86_FEATURE_SHSTK) || !shstk->size) + return 0; + + err =3D shstk_check_rstor_token(ia32, &new_ssp); + if (err) + return err; + + start_update_msrs(); + err =3D wrmsrl_safe(MSR_IA32_PL3_SSP, new_ssp); + end_update_msrs(); + + return err; +} diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index a06cb107c0e8..4d42debbb5ef 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -46,6 +46,7 @@ #include #include #include +#include =20 #ifdef CONFIG_X86_64 /* @@ -450,6 +451,9 @@ static int __setup_rt_frame(int sig, struct ksignal *= ksig, frame =3D get_sigframe(&ksig->ka, regs, sizeof(struct rt_sigframe), &fp= ); uc_flags =3D frame_uc_flags(regs); =20 + if (setup_signal_shadow_stack(0, ksig->ka.sa.sa_restorer)) + return -EFAULT; + if (!user_access_begin(frame, sizeof(*frame))) return -EFAULT; =20 @@ -555,6 +559,9 @@ static int x32_setup_rt_frame(struct ksignal *ksig, =20 uc_flags =3D frame_uc_flags(regs); =20 + if (setup_signal_shadow_stack(0, ksig->ka.sa.sa_restorer)) + return -EFAULT; + if (!user_access_begin(frame, sizeof(*frame))) return -EFAULT; =20 @@ -653,6 +660,9 @@ SYSCALL_DEFINE0(rt_sigreturn) if (restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags)) goto badframe; =20 + if (restore_signal_shadow_stack()) + goto badframe; + if (restore_altstack(&frame->uc.uc_stack)) goto badframe; =20 @@ -856,6 +866,9 @@ COMPAT_SYSCALL_DEFINE0(x32_rt_sigreturn) if (restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags)) goto badframe; =20 + if (restore_signal_shadow_stack()) + goto badframe; + if (compat_restore_altstack(&frame->uc.uc_stack)) goto badframe; =20 --=20 2.21.0