[PATCH 03/10] x86/cet: Signal handling for shadow stack

From: Yu-cheng Yu
Date: Thu Jun 07 2018 - 11:43:07 EST

Set and restore shadow stack pointer for signals.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
arch/x86/ia32/ia32_signal.c | 5 ++++
arch/x86/include/asm/cet.h | 7 +++++
arch/x86/include/uapi/asm/sigcontext.h | 4 +++
arch/x86/kernel/cet.c | 51 ++++++++++++++++++++++++++++++++++
arch/x86/kernel/signal.c | 11 ++++++++
5 files changed, 78 insertions(+)

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 86b1341cba9a..26a776baff7c 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -34,6 +34,7 @@
#include <asm/sigframe.h>
#include <asm/sighandling.h>
#include <asm/smap.h>
+#include <asm/cet.h>

/*
* Do a signal return; undo the signal stack.
@@ -74,6 +75,7 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
unsigned int tmpflags, err = 0;
void __user *buf;
u32 tmp;
+ u32 ssp;

/* Always make any pending restarted system calls return -EINTR */
current->restart_block.fn = do_no_restart_syscall;
@@ -104,9 +106,11 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,

get_user_ex(tmp, &sc->fpstate);
buf = compat_ptr(tmp);
+ get_user_ex(ssp, &sc->ssp);
} get_user_catch(err);

err |= fpu__restore_sig(buf, 1);
+ err |= cet_restore_signal((unsigned long)ssp);

force_iret();

@@ -194,6 +198,7 @@ static int ia32_setup_sigcontext(struct sigcontext_32 __user *sc,
put_user_ex(current->thread.trap_nr, &sc->trapno);
put_user_ex(current->thread.error_code, &sc->err);
put_user_ex(regs->ip, &sc->ip);
+ put_user_ex((u32)cet_get_shstk_ptr(), &sc->ssp);
put_user_ex(regs->cs, (unsigned int __user *)&sc->cs);
put_user_ex(regs->flags, &sc->flags);
put_user_ex(regs->sp, &sc->sp_at_signal);
diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index 9d5bc1efc9b7..5507469cb803 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -17,14 +17,21 @@ struct cet_stat {

#ifdef CONFIG_X86_INTEL_CET
unsigned long cet_get_shstk_ptr(void);
+int cet_push_shstk(int ia32, unsigned long ssp, unsigned long val);
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(int ia32, unsigned long addr);
#else
static inline unsigned long cet_get_shstk_ptr(void) { return 0; }
+static inline int cet_push_shstk(int ia32, unsigned long ssp,
+ unsigned long val) { return 0; }
static inline int cet_setup_shstk(void) { return 0; }
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 0; }
+static inline int cet_setup_signal(int ia32, unsigned long addr) { return 0; }
#endif

#endif /* __ASSEMBLY__ */
diff --git a/arch/x86/include/uapi/asm/sigcontext.h b/arch/x86/include/uapi/asm/sigcontext.h
index 844d60eb1882..6c8997a0156a 100644
--- a/arch/x86/include/uapi/asm/sigcontext.h
+++ b/arch/x86/include/uapi/asm/sigcontext.h
@@ -230,6 +230,7 @@ struct sigcontext_32 {
__u32 fpstate; /* Zero when no FPU/extended context */
__u32 oldmask;
__u32 cr2;
+ __u32 ssp;
};

/*
@@ -262,6 +263,7 @@ struct sigcontext_64 {
__u64 trapno;
__u64 oldmask;
__u64 cr2;
+ __u64 ssp;

/*
* fpstate is really (struct _fpstate *) or (struct _xstate *)
@@ -320,6 +322,7 @@ struct sigcontext {
struct _fpstate __user *fpstate;
__u32 oldmask;
__u32 cr2;
+ __u32 ssp;
};
# else /* __x86_64__: */
struct sigcontext {
@@ -377,6 +380,7 @@ struct sigcontext {
__u64 trapno;
__u64 oldmask;
__u64 cr2;
+ __u64 ssp;
struct _fpstate __user *fpstate; /* Zero when no FPU context */
# ifdef __ILP32__
__u32 __fpstate_pad;
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
index 8abbfd44322a..6f445ce94c83 100644
--- a/arch/x86/kernel/cet.c
+++ b/arch/x86/kernel/cet.c
@@ -17,6 +17,7 @@
#include <asm/fpu/xstate.h>
#include <asm/fpu/types.h>
#include <asm/cet.h>
+#include <asm/special_insns.h>

#define SHSTK_SIZE (0x8000 * (test_thread_flag(TIF_IA32) ? 4 : 8))

@@ -47,6 +48,24 @@ unsigned long cet_get_shstk_ptr(void)
return ptr;
}

+int cet_push_shstk(int ia32, unsigned long ssp, unsigned long val)
+{
+ if (val >= TASK_SIZE)
+ return -EINVAL;
+
+ if (IS_ENABLED(CONFIG_IA32_EMULATION) && ia32) {
+ if (!IS_ALIGNED(ssp, 4))
+ return -EINVAL;
+ cet_set_shstk_ptr(ssp);
+ return write_user_shstk_32(ssp, (unsigned int)val);
+ } else {
+ if (!IS_ALIGNED(ssp, 8))
+ return -EINVAL;
+ cet_set_shstk_ptr(ssp);
+ return write_user_shstk_64(ssp, val);
+ }
+}
+
static unsigned long shstk_mmap(unsigned long addr, unsigned long len)
{
struct mm_struct *mm = current->mm;
@@ -121,3 +140,35 @@ void cet_disable_free_shstk(struct task_struct *tsk)

tsk->thread.cet.shstk_enabled = 0;
}
+
+int cet_restore_signal(unsigned long ssp)
+{
+ if (!current->thread.cet.shstk_enabled)
+ return 0;
+ return cet_set_shstk_ptr(ssp);
+}
+
+int cet_setup_signal(int ia32, unsigned long rstor_addr)
+{
+ unsigned long ssp;
+ struct cet_stat *cet = &current->thread.cet;
+
+ if (!current->thread.cet.shstk_enabled)
+ return 0;
+
+ ssp = cet_get_shstk_ptr();
+
+ /*
+ * Put the restorer address on the shstk
+ */
+ if (ia32)
+ ssp -= sizeof(u32);
+ else
+ ssp -= sizeof(rstor_addr);
+
+ if (ssp >= (cet->shstk_base + cet->shstk_size) ||
+ ssp < cet->shstk_base)
+ return -EINVAL;
+
+ return cet_push_shstk(ia32, ssp, rstor_addr);
+}
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index da270b95fe4d..86fb897cae19 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -46,6 +46,7 @@

#include <asm/sigframe.h>
#include <asm/signal.h>
+#include <asm/cet.h>

#define COPY(x) do { \
get_user_ex(regs->x, &sc->x); \
@@ -102,6 +103,7 @@ static int restore_sigcontext(struct pt_regs *regs,
void __user *buf;
unsigned int tmpflags;
unsigned int err = 0;
+ unsigned long ssp = 0;

/* Always make any pending restarted system calls return -EINTR */
current->restart_block.fn = do_no_restart_syscall;
@@ -148,9 +150,11 @@ static int restore_sigcontext(struct pt_regs *regs,

get_user_ex(buf_val, &sc->fpstate);
buf = (void __user *)buf_val;
+ get_user_ex(ssp, &sc->ssp);
} get_user_catch(err);

err |= fpu__restore_sig(buf, IS_ENABLED(CONFIG_X86_32));
+ err |= cet_restore_signal(ssp);

force_iret();

@@ -193,6 +197,7 @@ int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate,
put_user_ex(current->thread.trap_nr, &sc->trapno);
put_user_ex(current->thread.error_code, &sc->err);
put_user_ex(regs->ip, &sc->ip);
+ put_user_ex(cet_get_shstk_ptr(), &sc->ssp);
#ifdef CONFIG_X86_32
put_user_ex(regs->cs, (unsigned int __user *)&sc->cs);
put_user_ex(regs->flags, &sc->flags);
@@ -742,6 +747,12 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
user_disable_single_step(current);

failed = (setup_rt_frame(ksig, regs) < 0);
+ if (!failed) {
+ unsigned long rstor = (unsigned long)ksig->ka.sa.sa_restorer;
+ int ia32 = is_ia32_frame(ksig);
+
+ failed = cet_setup_signal(ia32, rstor);
+ }
if (!failed) {
/*
* Clear the direction flag as per the ABI for function entry.
--
2.15.1