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Date: Fri, 21 May 2021 15:12:06 -0700
From: Yu-cheng Yu <yu-cheng.yu@...el.com>
To: x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, linux-mm@...ck.org,
linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
Arnd Bergmann <arnd@...db.de>,
Andy Lutomirski <luto@...nel.org>,
Balbir Singh <bsingharora@...il.com>,
Borislav Petkov <bp@...en8.de>,
Cyrill Gorcunov <gorcunov@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Eugene Syromiatnikov <esyr@...hat.com>,
Florian Weimer <fweimer@...hat.com>,
"H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Mike Kravetz <mike.kravetz@...cle.com>,
Nadav Amit <nadav.amit@...il.com>,
Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
Peter Zijlstra <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
Dave Martin <Dave.Martin@....com>,
Weijiang Yang <weijiang.yang@...el.com>,
Pengfei Xu <pengfei.xu@...el.com>,
Haitao Huang <haitao.huang@...el.com>
Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v27 26/31] x86/cet/shstk: Handle signals for shadow stack
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 <yu-cheng.yu@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Cyrill Gorcunov <gorcunov@...il.com>
Cc: Florian Weimer <fweimer@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
---
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 <asm/sigframe.h>
#include <asm/sighandling.h>
#include <asm/smap.h>
+#include <asm/cet.h>
static inline void reload_segments(struct sigcontext_32 *sc)
{
@@ -113,6 +114,10 @@ COMPAT_SYSCALL_DEFINE0(sigreturn)
if (ia32_restore_sigcontext(regs, &frame->sc))
goto badframe;
+
+ if (restore_signal_shadow_stack())
+ goto badframe;
+
return regs->ax;
badframe:
@@ -138,6 +143,9 @@ COMPAT_SYSCALL_DEFINE0(rt_sigreturn)
if (ia32_restore_sigcontext(regs, &frame->uc.uc_mcontext))
goto badframe;
+ if (restore_signal_shadow_stack())
+ goto badframe;
+
if (compat_restore_altstack(&frame->uc.uc_stack))
goto badframe;
@@ -262,6 +270,9 @@ int ia32_setup_frame(int sig, struct ksignal *ksig,
restorer = &frame->retcode;
}
+ if (setup_signal_shadow_stack(1, restorer))
+ return -EFAULT;
+
if (!user_access_begin(frame, sizeof(*frame)))
return -EFAULT;
@@ -319,6 +330,15 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
frame = get_sigframe(ksig, regs, sizeof(*frame), &fp);
+ if (ksig->ka.sa.sa_flags & SA_RESTORER)
+ restorer = ksig->ka.sa.sa_restorer;
+ else
+ restorer = 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;
@@ -334,11 +354,6 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
unsafe_put_user(0, &frame->uc.uc_link, Efault);
unsafe_compat_save_altstack(&frame->uc.uc_stack, regs->sp, Efault);
- if (ksig->ka.sa.sa_flags & SA_RESTORER)
- restorer = ksig->ka.sa.sa_restorer;
- else
- restorer = current->mm->context.vdso +
- vdso_image_32.sym___kernel_rt_sigreturn;
unsafe_put_user(ptr_to_compat(restorer), &frame->pretcode, Efault);
/*
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, unsigned 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 *restorer) { return 0; }
+static inline int restore_signal_shadow_stack(void) { return 0; }
#endif
#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 long *new_ssp)
return 0;
}
+
+int setup_signal_shadow_stack(int ia32, void __user *restorer)
+{
+ struct thread_shstk *shstk = ¤t->thread.shstk;
+ unsigned long new_ssp;
+ int err;
+
+ if (!cpu_feature_enabled(X86_FEATURE_SHSTK) || !shstk->size)
+ return 0;
+
+ err = shstk_setup_rstor_token(ia32, (unsigned long)restorer,
+ &new_ssp);
+ if (err)
+ return err;
+
+ start_update_msrs();
+ err = wrmsrl_safe(MSR_IA32_PL3_SSP, new_ssp);
+ end_update_msrs();
+
+ return err;
+}
+
+int restore_signal_shadow_stack(void)
+{
+ struct thread_shstk *shstk = ¤t->thread.shstk;
+ int ia32 = in_ia32_syscall();
+ unsigned long new_ssp;
+ int err;
+
+ if (!cpu_feature_enabled(X86_FEATURE_SHSTK) || !shstk->size)
+ return 0;
+
+ err = shstk_check_rstor_token(ia32, &new_ssp);
+ if (err)
+ return err;
+
+ start_update_msrs();
+ err = 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 <asm/syscall.h>
#include <asm/sigframe.h>
#include <asm/signal.h>
+#include <asm/cet.h>
#ifdef CONFIG_X86_64
/*
@@ -450,6 +451,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
frame = get_sigframe(&ksig->ka, regs, sizeof(struct rt_sigframe), &fp);
uc_flags = frame_uc_flags(regs);
+ if (setup_signal_shadow_stack(0, ksig->ka.sa.sa_restorer))
+ return -EFAULT;
+
if (!user_access_begin(frame, sizeof(*frame)))
return -EFAULT;
@@ -555,6 +559,9 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
uc_flags = frame_uc_flags(regs);
+ if (setup_signal_shadow_stack(0, ksig->ka.sa.sa_restorer))
+ return -EFAULT;
+
if (!user_access_begin(frame, sizeof(*frame)))
return -EFAULT;
@@ -653,6 +660,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
if (restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
+ if (restore_signal_shadow_stack())
+ goto badframe;
+
if (restore_altstack(&frame->uc.uc_stack))
goto badframe;
@@ -856,6 +866,9 @@ COMPAT_SYSCALL_DEFINE0(x32_rt_sigreturn)
if (restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
+ if (restore_signal_shadow_stack())
+ goto badframe;
+
if (compat_restore_altstack(&frame->uc.uc_stack))
goto badframe;
--
2.21.0
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