diff mbox series

[v27,23/31] x86/cet/shstk: Add user-mode shadow stack support

Message ID 20210521221211.29077-24-yu-cheng.yu@intel.com (mailing list archive)
State New, archived
Headers show
Series Control-flow Enforcement: Shadow Stack | expand

Commit Message

Yu-cheng Yu May 21, 2021, 10:12 p.m. UTC 
Introduce basic shadow stack enabling/disabling/allocation routines.
A task's shadow stack is allocated from memory with VM_SHADOW_STACK flag
and has a fixed size of min(RLIMIT_STACK, 4GB).

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Kees Cook <keescook@chromium.org>
---
v27:
- Change 'struct cet_status' to 'struct thread_shstk', and change member
  types from unsigned long to u64.
- Re-order local variables in reverse order of length.
- WARN_ON_ONCE() when vm_munmap() fails.

 arch/x86/include/asm/cet.h       |  30 +++++++
 arch/x86/include/asm/processor.h |   5 ++
 arch/x86/kernel/Makefile         |   1 +
 arch/x86/kernel/shstk.c          | 130 +++++++++++++++++++++++++++++++
 4 files changed, 166 insertions(+)
 create mode 100644 arch/x86/include/asm/cet.h
 create mode 100644 arch/x86/kernel/shstk.c

Comments

Edgecombe, Rick P July 19, 2021, 6:23 p.m. UTC | #1 
On Fri, 2021-05-21 at 15:12 -0700, Yu-cheng Yu wrote:
> Introduce basic shadow stack enabling/disabling/allocation routines.
> A task's shadow stack is allocated from memory with VM_SHADOW_STACK
> flag
> and has a fixed size of min(RLIMIT_STACK, 4GB).
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Cc: Kees Cook <keescook@chromium.org>
> ---
> v27:
> - Change 'struct cet_status' to 'struct thread_shstk', and change
> member
>   types from unsigned long to u64.
> - Re-order local variables in reverse order of length.
> - WARN_ON_ONCE() when vm_munmap() fails.
> 
>  arch/x86/include/asm/cet.h       |  30 +++++++
>  arch/x86/include/asm/processor.h |   5 ++
>  arch/x86/kernel/Makefile         |   1 +
>  arch/x86/kernel/shstk.c          | 130
> +++++++++++++++++++++++++++++++
>  4 files changed, 166 insertions(+)
>  create mode 100644 arch/x86/include/asm/cet.h
>  create mode 100644 arch/x86/kernel/shstk.c
> 
> diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
> new file mode 100644
> index 000000000000..6432baf4de1f
> --- /dev/null
> +++ b/arch/x86/include/asm/cet.h
> @@ -0,0 +1,30 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_X86_CET_H
> +#define _ASM_X86_CET_H
> +
> +#ifndef __ASSEMBLY__
> +#include <linux/types.h>
> +
> +struct task_struct;
> +
> +/*
> + * Per-thread CET status
> + */
> +struct thread_shstk {
> +       u64     base;
> +       u64     size;
> +};
> +
> +#ifdef CONFIG_X86_SHADOW_STACK
> +int shstk_setup(void);
> +void shstk_free(struct task_struct *p);
> +void shstk_disable(void);
> +#else
> +static inline int shstk_setup(void) { return 0; }
> +static inline void shstk_free(struct task_struct *p) {}
> +static inline void shstk_disable(void) {}
> +#endif
> +
> +#endif /* __ASSEMBLY__ */
> +
> +#endif /* _ASM_X86_CET_H */
> diff --git a/arch/x86/include/asm/processor.h
> b/arch/x86/include/asm/processor.h
> index 556b2b17c3e2..7eb56a837cfa 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -27,6 +27,7 @@ struct vm86;
>  #include <asm/unwind_hints.h>
>  #include <asm/vmxfeatures.h>
>  #include <asm/vdso/processor.h>
> +#include <asm/cet.h>
>  
>  #include <linux/personality.h>
>  #include <linux/cache.h>
> @@ -518,6 +519,10 @@ struct thread_struct {
>  
>         unsigned int            sig_on_uaccess_err:1;
>  
> +#ifdef CONFIG_X86_SHADOW_STACK
> +       struct thread_shstk     shstk;
> +#endif
> +
>         /* Floating point and extended processor state */
>         struct fpu              fpu;
>         /*
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 0f66682ac02a..b0e599102277 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -149,6 +149,7 @@ obj-$(CONFIG_UNWINDER_FRAME_POINTER)        +=
> unwind_frame.o
>  obj-$(CONFIG_UNWINDER_GUESS)           += unwind_guess.o
>  
>  obj-$(CONFIG_AMD_MEM_ENCRYPT)          += sev.o
> +obj-$(CONFIG_X86_SHADOW_STACK)         += shstk.o
>  ###
>  # 64 bit specific files
>  ifeq ($(CONFIG_X86_64),y)
> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
> new file mode 100644
> index 000000000000..5ea2b494e9f9
> --- /dev/null
> +++ b/arch/x86/kernel/shstk.c
> @@ -0,0 +1,130 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * shstk.c - Intel shadow stack support
> + *
> + * Copyright (c) 2021, Intel Corporation.
> + * Yu-cheng Yu <yu-cheng.yu@intel.com>
> + */
> +
> +#include <linux/types.h>
> +#include <linux/mm.h>
> +#include <linux/mman.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +#include <linux/sched/signal.h>
> +#include <linux/compat.h>
> +#include <linux/sizes.h>
> +#include <linux/user.h>
> +#include <asm/msr.h>
> +#include <asm/fpu/internal.h>
> +#include <asm/fpu/xstate.h>
> +#include <asm/fpu/types.h>
> +#include <asm/cet.h>
> +
> +static void start_update_msrs(void)
> +{
> +       fpregs_lock();
> +       if (test_thread_flag(TIF_NEED_FPU_LOAD))
> +               __fpregs_load_activate();
> +}
> +
> +static void end_update_msrs(void)
> +{
> +       fpregs_unlock();
> +}
> +
> +static unsigned long alloc_shstk(unsigned long size)
> +{
> +       int flags = MAP_ANONYMOUS | MAP_PRIVATE;
> +       struct mm_struct *mm = current->mm;
> +       unsigned long addr, populate;
> +
> +       mmap_write_lock(mm);
> +       addr = do_mmap(NULL, 0, size, PROT_READ, flags,
> VM_SHADOW_STACK, 0,
> +                      &populate, NULL);
> +       mmap_write_unlock(mm);
> +
> +       return addr;
> +}
> +
> +int shstk_setup(void)
> +{
> +       struct thread_shstk *shstk = &current->thread.shstk;
> +       unsigned long addr, size;
> +
> +       if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
> +               return -EOPNOTSUPP;
The only caller of this will skip it if
!cpu_feature_enabled(X86_FEATURE_SHSTK), so this is dead logic. Same
pattern in the IBT patch.

> +
> +       size = round_up(min_t(unsigned long long,
> rlimit(RLIMIT_STACK), SZ_4G), PAGE_SIZE);
> +       addr = alloc_shstk(size);
> +       if (IS_ERR_VALUE(addr))
> +               return PTR_ERR((void *)addr);
> +
> +       shstk->base = addr;
> +       shstk->size = size;
> +
> +       start_update_msrs();
> +       wrmsrl(MSR_IA32_PL3_SSP, addr + size);
> +       wrmsrl(MSR_IA32_U_CET, CET_SHSTK_EN);
> +       end_update_msrs();
> +
> +       return 0;
> +}
> +
> +void shstk_free(struct task_struct *tsk)
> +{
> +       struct thread_shstk *shstk = &tsk->thread.shstk;
> +
> +       if (!cpu_feature_enabled(X86_FEATURE_SHSTK) ||
> +           !shstk->size ||
> +           !shstk->base)
> +               return;
> +
> +       if (!tsk->mm)
> +               return;
> +
> +       while (1) {
> +               int r;
> +
> +               r = vm_munmap(shstk->base, shstk->size);
> +
> +               /*
> +                * vm_munmap() returns -EINTR when mmap_lock is held
> by
> +                * something else, and that lock should not be held
> for a
> +                * long time.  Retry it for the case.
> +                */
> +               if (r == -EINTR) {
> +                       cond_resched();
> +                       continue;
> +               }
> +
> +               /*
> +                * For all other types of vm_munmap() failure, either
> the
> +                * system is out of memory or there is bug.
> +                */
> +               WARN_ON_ONCE(r);
> +               break;
> +       }
> +
> +       shstk->base = 0;
> +       shstk->size = 0;
> +}
> +
> +void shstk_disable(void)
> +{
> +       struct thread_shstk *shstk = &current->thread.shstk;
> +       u64 msr_val;
> +
> +       if (!cpu_feature_enabled(X86_FEATURE_SHSTK) ||
> +           !shstk->size ||
> +           !shstk->base)
> +               return;
> +
> +       start_update_msrs();
> +       rdmsrl(MSR_IA32_U_CET, msr_val);
> +       wrmsrl(MSR_IA32_U_CET, msr_val & ~CET_SHSTK_EN);
> +       wrmsrl(MSR_IA32_PL3_SSP, 0);
> +       end_update_msrs();
> +
> +       shstk_free(current);
> +}
Yu-cheng Yu July 20, 2021, 5:13 p.m. UTC | #2 
On 7/19/2021 11:23 AM, Edgecombe, Rick P wrote:
> On Fri, 2021-05-21 at 15:12 -0700, Yu-cheng Yu wrote:
>> Introduce basic shadow stack enabling/disabling/allocation routines.
>> A task's shadow stack is allocated from memory with VM_SHADOW_STACK
>> flag
>> and has a fixed size of min(RLIMIT_STACK, 4GB).
>>
>> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
>> Cc: Kees Cook <keescook@chromium.org>

[...]

>> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
>> new file mode 100644
>> index 000000000000..5ea2b494e9f9
>> --- /dev/null
>> +++ b/arch/x86/kernel/shstk.c

[...]

>> +int shstk_setup(void)
>> +{
>> +       struct thread_shstk *shstk = &current->thread.shstk;
>> +       unsigned long addr, size;
>> +
>> +       if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
>> +               return -EOPNOTSUPP;
> The only caller of this will skip it if
> !cpu_feature_enabled(X86_FEATURE_SHSTK), so this is dead logic. Same
> pattern in the IBT patch.
> 

Indeed that is the case.  We can simply remove the test of 
X86_FEATURE_SHSTK.

Thanks,
Yu-cheng
diff mbox series

Patch

diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
new file mode 100644
index 000000000000..6432baf4de1f
--- /dev/null
+++ b/arch/x86/include/asm/cet.h
@@ -0,0 +1,30 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_CET_H
+#define _ASM_X86_CET_H
+
+#ifndef __ASSEMBLY__
+#include <linux/types.h>
+
+struct task_struct;
+
+/*
+ * Per-thread CET status
+ */
+struct thread_shstk {
+	u64	base;
+	u64	size;
+};
+
+#ifdef CONFIG_X86_SHADOW_STACK
+int shstk_setup(void);
+void shstk_free(struct task_struct *p);
+void shstk_disable(void);
+#else
+static inline int shstk_setup(void) { return 0; }
+static inline void shstk_free(struct task_struct *p) {}
+static inline void shstk_disable(void) {}
+#endif
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* _ASM_X86_CET_H */
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 556b2b17c3e2..7eb56a837cfa 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -27,6 +27,7 @@  struct vm86;
 #include <asm/unwind_hints.h>
 #include <asm/vmxfeatures.h>
 #include <asm/vdso/processor.h>
+#include <asm/cet.h>
 
 #include <linux/personality.h>
 #include <linux/cache.h>
@@ -518,6 +519,10 @@  struct thread_struct {
 
 	unsigned int		sig_on_uaccess_err:1;
 
+#ifdef CONFIG_X86_SHADOW_STACK
+	struct thread_shstk	shstk;
+#endif
+
 	/* Floating point and extended processor state */
 	struct fpu		fpu;
 	/*
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 0f66682ac02a..b0e599102277 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -149,6 +149,7 @@  obj-$(CONFIG_UNWINDER_FRAME_POINTER)	+= unwind_frame.o
 obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
 
 obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= sev.o
+obj-$(CONFIG_X86_SHADOW_STACK)		+= shstk.o
 ###
 # 64 bit specific files
 ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
new file mode 100644
index 000000000000..5ea2b494e9f9
--- /dev/null
+++ b/arch/x86/kernel/shstk.c
@@ -0,0 +1,130 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * shstk.c - Intel shadow stack support
+ *
+ * Copyright (c) 2021, Intel Corporation.
+ * Yu-cheng Yu <yu-cheng.yu@intel.com>
+ */
+
+#include <linux/types.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/sched/signal.h>
+#include <linux/compat.h>
+#include <linux/sizes.h>
+#include <linux/user.h>
+#include <asm/msr.h>
+#include <asm/fpu/internal.h>
+#include <asm/fpu/xstate.h>
+#include <asm/fpu/types.h>
+#include <asm/cet.h>
+
+static void start_update_msrs(void)
+{
+	fpregs_lock();
+	if (test_thread_flag(TIF_NEED_FPU_LOAD))
+		__fpregs_load_activate();
+}
+
+static void end_update_msrs(void)
+{
+	fpregs_unlock();
+}
+
+static unsigned long alloc_shstk(unsigned long size)
+{
+	int flags = MAP_ANONYMOUS | MAP_PRIVATE;
+	struct mm_struct *mm = current->mm;
+	unsigned long addr, populate;
+
+	mmap_write_lock(mm);
+	addr = do_mmap(NULL, 0, size, PROT_READ, flags, VM_SHADOW_STACK, 0,
+		       &populate, NULL);
+	mmap_write_unlock(mm);
+
+	return addr;
+}
+
+int shstk_setup(void)
+{
+	struct thread_shstk *shstk = &current->thread.shstk;
+	unsigned long addr, size;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
+		return -EOPNOTSUPP;
+
+	size = round_up(min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G), PAGE_SIZE);
+	addr = alloc_shstk(size);
+	if (IS_ERR_VALUE(addr))
+		return PTR_ERR((void *)addr);
+
+	shstk->base = addr;
+	shstk->size = size;
+
+	start_update_msrs();
+	wrmsrl(MSR_IA32_PL3_SSP, addr + size);
+	wrmsrl(MSR_IA32_U_CET, CET_SHSTK_EN);
+	end_update_msrs();
+
+	return 0;
+}
+
+void shstk_free(struct task_struct *tsk)
+{
+	struct thread_shstk *shstk = &tsk->thread.shstk;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SHSTK) ||
+	    !shstk->size ||
+	    !shstk->base)
+		return;
+
+	if (!tsk->mm)
+		return;
+
+	while (1) {
+		int r;
+
+		r = vm_munmap(shstk->base, shstk->size);
+
+		/*
+		 * vm_munmap() returns -EINTR when mmap_lock is held by
+		 * something else, and that lock should not be held for a
+		 * long time.  Retry it for the case.
+		 */
+		if (r == -EINTR) {
+			cond_resched();
+			continue;
+		}
+
+		/*
+		 * For all other types of vm_munmap() failure, either the
+		 * system is out of memory or there is bug.
+		 */
+		WARN_ON_ONCE(r);
+		break;
+	}
+
+	shstk->base = 0;
+	shstk->size = 0;
+}
+
+void shstk_disable(void)
+{
+	struct thread_shstk *shstk = &current->thread.shstk;
+	u64 msr_val;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SHSTK) ||
+	    !shstk->size ||
+	    !shstk->base)
+		return;
+
+	start_update_msrs();
+	rdmsrl(MSR_IA32_U_CET, msr_val);
+	wrmsrl(MSR_IA32_U_CET, msr_val & ~CET_SHSTK_EN);
+	wrmsrl(MSR_IA32_PL3_SSP, 0);
+	end_update_msrs();
+
+	shstk_free(current);
+}