When shadow stack is enabled, a task's shadow stack states must be saved
along with the signal context and later restored in sigreturn. However,
currently there is no systematic facility for extending a signal context.
Introduce a signal context extension struct 'sc_ext', which is used to save
shadow stack restore token address and WAIT_ENDBR status[1]. The extension
is located above the fpu states, plus alignment.
Introduce routines for the allocation, save, and restore for sc_ext:
- fpu__alloc_sigcontext_ext(),
- save_extra_state_to_sigframe(),
- get_extra_state_from_sigframe(),
- restore_extra_state().
[1] WAIT_ENDBR will be introduced later in the Indirect Branch Tracking
series, but add that into sc_ext now to keep the struct stable in case
the IBT series is applied later.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
---
v24:
- Split out shadow stack token routines to a separate patch.
- Put signal frame save/restore routines to fpu/signal.c and re-name accordingly.
arch/x86/ia32/ia32_signal.c | 16 +++
arch/x86/include/asm/cet.h | 2 +
arch/x86/include/asm/fpu/internal.h | 2 +
arch/x86/include/uapi/asm/sigcontext.h | 9 ++
arch/x86/kernel/fpu/signal.c | 143 +++++++++++++++++++++++++
arch/x86/kernel/signal.c | 9 ++
6 files changed, 181 insertions(+)
diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 5e3d9b7fd5fb..96b87c5f0bbe 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -205,6 +205,7 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
void __user **fpstate)
{
unsigned long sp, fx_aligned, math_size;
+ void __user *restorer = NULL;
/* Default to using normal stack */
sp = regs->sp;
@@ -218,8 +219,23 @@ 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;
+ if (ksig->ka.sa.sa_flags & SA_RESTORER) {
+ restorer = ksig->ka.sa.sa_restorer;
+ } else if (current->mm->context.vdso) {
+ if (ksig->ka.sa.sa_flags & SA_SIGINFO)
+ restorer = current->mm->context.vdso +
+ vdso_image_32.sym___kernel_rt_sigreturn;
+ else
+ restorer = current->mm->context.vdso +
+ vdso_image_32.sym___kernel_sigreturn;
+ }
+
sp = fpu__alloc_mathframe(sp, 1, &fx_aligned, &math_size);
*fpstate = (struct _fpstate_32 __user *) sp;
+
+ if (save_extra_state_to_sigframe(1, *fpstate, (unsigned long)restorer))
+ return (void __user *)-1L;
+
if (copy_fpstate_to_sigframe(*fpstate, (void __user *)fx_aligned,
math_size) < 0)
return (void __user *) -1L;
diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index ef6155213b7e..5e66919bd2fe 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -6,6 +6,8 @@
#include <linux/types.h>
struct task_struct;
+struct sc_ext;
+
/*
* Per-thread CET status
*/
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 8d33ad80704f..eb01eb6ea55d 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -443,6 +443,8 @@ static inline void copy_kernel_to_fpregs(union fpregs_state *fpstate)
__copy_kernel_to_fpregs(fpstate, -1);
}
+extern int save_extra_state_to_sigframe(int ia32, void __user *fp,
+ unsigned long restorer);
extern int copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size);
/*
diff --git a/arch/x86/include/uapi/asm/sigcontext.h b/arch/x86/include/uapi/asm/sigcontext.h
index 844d60eb1882..cf2d55db3be4 100644
--- a/arch/x86/include/uapi/asm/sigcontext.h
+++ b/arch/x86/include/uapi/asm/sigcontext.h
@@ -196,6 +196,15 @@ struct _xstate {
/* New processor state extensions go here: */
};
+/*
+ * Located at the end of sigcontext->fpstate, aligned to 8.
+ */
+struct sc_ext {
+ unsigned long total_size;
+ unsigned long ssp;
+ unsigned long wait_endbr;
+};
+
/*
* The 32-bit signal frame:
*/
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index a4ec65317a7f..2e56f2fe8be0 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -52,6 +52,123 @@ static inline int check_for_xstate(struct fxregs_state __user *buf,
return 0;
}
+int save_extra_state_to_sigframe(int ia32, void __user *fp, unsigned long restorer)
+{
+ int err = 0;
+
+#ifdef CONFIG_X86_CET
+ struct cet_status *cet = ¤t->thread.cet;
+ unsigned long token_addr = 0, new_ssp = 0;
+ struct sc_ext ext = {};
+
+ if (!cpu_feature_enabled(X86_FEATURE_CET))
+ return 0;
+
+ if (cet->shstk_size) {
+ err = shstk_setup_rstor_token(ia32, restorer,
+ &token_addr, &new_ssp);
+ if (err)
+ return err;
+
+ ext.ssp = token_addr;
+
+ fpregs_lock();
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ __fpregs_load_activate();
+ if (new_ssp)
+ wrmsrl(MSR_IA32_PL3_SSP, new_ssp);
+ fpregs_unlock();
+ }
+
+ if (ext.ssp) {
+ void __user *p = fp;
+
+ ext.total_size = sizeof(ext);
+
+ p = fp;
+ if (ia32)
+ p += sizeof(struct fregs_state);
+
+ p += 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 get_extra_state_from_sigframe(int ia32, void __user *fp, struct sc_ext *ext)
+{
+ int err = 0;
+
+#ifdef CONFIG_X86_CET
+ struct cet_status *cet = ¤t->thread.cet;
+ void __user *p;
+
+ if (!cpu_feature_enabled(X86_FEATURE_CET))
+ return 0;
+
+ if (!cet->shstk_size)
+ return 0;
+
+ memset(ext, 0, sizeof(*ext));
+
+ p = fp;
+ if (ia32)
+ p += sizeof(struct fregs_state);
+
+ p += 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;
+
+ if (cet->shstk_size)
+ err = shstk_check_rstor_token(ia32, ext->ssp, &ext->ssp);
+#endif
+ return err;
+}
+
+/*
+ * Called from __fpu__restore_sig() and XSAVES buffer is protected by
+ * set_thread_flag(TIF_NEED_FPU_LOAD) in the slow path.
+ */
+void restore_extra_state(struct sc_ext *sc_ext)
+{
+#ifdef CONFIG_X86_CET
+ struct cet_status *cet = ¤t->thread.cet;
+ struct cet_user_state *cet_user_state;
+ u64 msr_val = 0;
+
+ if (!cpu_feature_enabled(X86_FEATURE_CET))
+ return;
+
+ cet_user_state = get_xsave_addr(¤t->thread.fpu.state.xsave,
+ XFEATURE_CET_USER);
+ if (!cet_user_state)
+ return;
+
+ if (cet->shstk_size) {
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ cet_user_state->user_ssp = sc_ext->ssp;
+ else
+ wrmsrl(MSR_IA32_PL3_SSP, sc_ext->ssp);
+
+ msr_val |= CET_SHSTK_EN;
+ }
+
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ cet_user_state->user_cet = msr_val;
+ else
+ wrmsrl(MSR_IA32_U_CET, msr_val);
+#endif
+}
+
/*
* Signal frame handlers.
*/
@@ -295,6 +412,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
struct task_struct *tsk = current;
struct fpu *fpu = &tsk->thread.fpu;
struct user_i387_ia32_struct env;
+ struct sc_ext sc_ext;
u64 user_xfeatures = 0;
int fx_only = 0;
int ret = 0;
@@ -335,6 +453,10 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
if ((unsigned long)buf_fx % 64)
fx_only = 1;
+ ret = get_extra_state_from_sigframe(ia32_fxstate, buf, &sc_ext);
+ if (ret)
+ return ret;
+
if (!ia32_fxstate) {
/*
* Attempt to restore the FPU registers directly from user
@@ -349,6 +471,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
pagefault_enable();
if (!ret) {
+ restore_extra_state(&sc_ext);
+
/*
* Restore supervisor states: previous context switch
* etc has done XSAVES and saved the supervisor states
@@ -423,6 +547,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
if (unlikely(init_bv))
copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
+ restore_extra_state(&sc_ext);
+
/*
* Restore previously saved supervisor xstates along with
* copied-in user xstates.
@@ -491,12 +617,29 @@ int fpu__restore_sig(void __user *buf, int ia32_frame)
return __fpu__restore_sig(buf, buf_fx, size);
}
+static unsigned long fpu__alloc_sigcontext_ext(unsigned long sp)
+{
+#ifdef CONFIG_X86_CET
+ struct cet_status *cet = ¤t->thread.cet;
+
+ /*
+ * sigcontext_ext is at: fpu + fpu_user_xstate_size +
+ * FP_XSTATE_MAGIC2_SIZE, then aligned to 8.
+ */
+ if (cet->shstk_size)
+ sp -= (sizeof(struct sc_ext) + 8);
+#endif
+ return sp;
+}
+
unsigned long
fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
unsigned long *buf_fx, unsigned long *size)
{
unsigned long frame_size = xstate_sigframe_size();
+ sp = fpu__alloc_sigcontext_ext(sp);
+
*buf_fx = sp = round_down(sp - frame_size, 64);
if (ia32_frame && use_fxsr()) {
frame_size += sizeof(struct fregs_state);
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index f306e85a08a6..111faa5a398f 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -239,6 +239,9 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
unsigned long buf_fx = 0;
int onsigstack = on_sig_stack(sp);
int ret;
+#ifdef CONFIG_X86_64
+ void __user *restorer = NULL;
+#endif
/* redzone */
if (IS_ENABLED(CONFIG_X86_64))
@@ -270,6 +273,12 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
if (onsigstack && !likely(on_sig_stack(sp)))
return (void __user *)-1L;
+#ifdef CONFIG_X86_64
+ if (ka->sa.sa_flags & SA_RESTORER)
+ restorer = ka->sa.sa_restorer;
+ ret = save_extra_state_to_sigframe(0, *fpstate, (unsigned long)restorer);
+#endif
+
/* save i387 and extended state */
ret = copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size);
if (ret < 0)
--
2.21.0
