diff mbox series

[v12,12/28] riscv: Implements arch agnostic shadow stack prctls

Message ID 20250314-v5_user_cfi_series-v12-12-e51202b53138@rivosinc.com (mailing list archive)
State New
Headers show
Series riscv control-flow integrity for usermode | expand

Commit Message

Deepak Gupta March 14, 2025, 9:39 p.m. UTC 
Implement architecture agnostic prctls() interface for setting and getting
shadow stack status.

prctls implemented are PR_GET_SHADOW_STACK_STATUS,
PR_SET_SHADOW_STACK_STATUS and PR_LOCK_SHADOW_STACK_STATUS.

As part of PR_SET_SHADOW_STACK_STATUS/PR_GET_SHADOW_STACK_STATUS, only
PR_SHADOW_STACK_ENABLE is implemented because RISCV allows each mode to
write to their own shadow stack using `sspush` or `ssamoswap`.

PR_LOCK_SHADOW_STACK_STATUS locks current configuration of shadow stack
enabling.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
 arch/riscv/include/asm/usercfi.h |  18 ++++++-
 arch/riscv/kernel/process.c      |   8 +++
 arch/riscv/kernel/usercfi.c      | 110 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 135 insertions(+), 1 deletion(-)

Comments

Zong Li March 17, 2025, 1:29 a.m. UTC | #1 
On Sat, Mar 15, 2025 at 6:51 AM Deepak Gupta <debug@rivosinc.com> wrote:
>
> Implement architecture agnostic prctls() interface for setting and getting
> shadow stack status.
>
> prctls implemented are PR_GET_SHADOW_STACK_STATUS,
> PR_SET_SHADOW_STACK_STATUS and PR_LOCK_SHADOW_STACK_STATUS.
>
> As part of PR_SET_SHADOW_STACK_STATUS/PR_GET_SHADOW_STACK_STATUS, only
> PR_SHADOW_STACK_ENABLE is implemented because RISCV allows each mode to
> write to their own shadow stack using `sspush` or `ssamoswap`.
>
> PR_LOCK_SHADOW_STACK_STATUS locks current configuration of shadow stack
> enabling.
>
> Signed-off-by: Deepak Gupta <debug@rivosinc.com>
> ---
>  arch/riscv/include/asm/usercfi.h |  18 ++++++-
>  arch/riscv/kernel/process.c      |   8 +++
>  arch/riscv/kernel/usercfi.c      | 110 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 135 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h
> index 82d28ac98d76..c4dcd256f19a 100644
> --- a/arch/riscv/include/asm/usercfi.h
> +++ b/arch/riscv/include/asm/usercfi.h
> @@ -7,6 +7,7 @@
>
>  #ifndef __ASSEMBLY__
>  #include <linux/types.h>
> +#include <linux/prctl.h>
>
>  struct task_struct;
>  struct kernel_clone_args;
> @@ -14,7 +15,8 @@ struct kernel_clone_args;
>  #ifdef CONFIG_RISCV_USER_CFI
>  struct cfi_status {
>         unsigned long ubcfi_en : 1; /* Enable for backward cfi. */
> -       unsigned long rsvd : ((sizeof(unsigned long) * 8) - 1);
> +       unsigned long ubcfi_locked : 1;
> +       unsigned long rsvd : ((sizeof(unsigned long) * 8) - 2);
>         unsigned long user_shdw_stk; /* Current user shadow stack pointer */
>         unsigned long shdw_stk_base; /* Base address of shadow stack */
>         unsigned long shdw_stk_size; /* size of shadow stack */
> @@ -27,6 +29,12 @@ void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, unsigned
>  unsigned long get_shstk_base(struct task_struct *task, unsigned long *size);
>  void set_active_shstk(struct task_struct *task, unsigned long shstk_addr);
>  bool is_shstk_enabled(struct task_struct *task);
> +bool is_shstk_locked(struct task_struct *task);
> +bool is_shstk_allocated(struct task_struct *task);
> +void set_shstk_lock(struct task_struct *task);
> +void set_shstk_status(struct task_struct *task, bool enable);
> +
> +#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK (PR_SHADOW_STACK_ENABLE)
>
>  #else
>
> @@ -42,6 +50,14 @@ bool is_shstk_enabled(struct task_struct *task);
>
>  #define is_shstk_enabled(task) false
>
> +#define is_shstk_locked(task) false
> +
> +#define is_shstk_allocated(task) false
> +
> +#define set_shstk_lock(task)
> +
> +#define set_shstk_status(task, enable)
> +
>  #endif /* CONFIG_RISCV_USER_CFI */
>
>  #endif /* __ASSEMBLY__ */
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 99acb6342a37..cd11667593fe 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -153,6 +153,14 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
>         regs->epc = pc;
>         regs->sp = sp;
>
> +       /*
> +        * clear shadow stack state on exec.
> +        * libc will set it later via prctl.
> +        */
> +       set_shstk_status(current, false);
> +       set_shstk_base(current, 0, 0);
> +       set_active_shstk(current, 0);
> +
>  #ifdef CONFIG_64BIT
>         regs->status &= ~SR_UXL;
>
> diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
> index 73cf87dab186..b93b324eed26 100644
> --- a/arch/riscv/kernel/usercfi.c
> +++ b/arch/riscv/kernel/usercfi.c
> @@ -24,6 +24,16 @@ bool is_shstk_enabled(struct task_struct *task)
>         return task->thread_info.user_cfi_state.ubcfi_en ? true : false;
>  }
>
> +bool is_shstk_allocated(struct task_struct *task)
> +{
> +       return task->thread_info.user_cfi_state.shdw_stk_base ? true : false;
> +}
> +
> +bool is_shstk_locked(struct task_struct *task)
> +{
> +       return task->thread_info.user_cfi_state.ubcfi_locked ? true : false;
> +}
> +
>  void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, unsigned long size)
>  {
>         task->thread_info.user_cfi_state.shdw_stk_base = shstk_addr;
> @@ -42,6 +52,26 @@ void set_active_shstk(struct task_struct *task, unsigned long shstk_addr)
>         task->thread_info.user_cfi_state.user_shdw_stk = shstk_addr;
>  }
>
> +void set_shstk_status(struct task_struct *task, bool enable)
> +{
> +       if (!cpu_supports_shadow_stack())
> +               return;
> +
> +       task->thread_info.user_cfi_state.ubcfi_en = enable ? 1 : 0;
> +
> +       if (enable)
> +               task->thread.envcfg |= ENVCFG_SSE;
> +       else
> +               task->thread.envcfg &= ~ENVCFG_SSE;
> +
> +       csr_write(CSR_ENVCFG, task->thread.envcfg);
> +}
> +
> +void set_shstk_lock(struct task_struct *task)
> +{
> +       task->thread_info.user_cfi_state.ubcfi_locked = 1;
> +}
> +
>  /*
>   * If size is 0, then to be compatible with regular stack we want it to be as big as
>   * regular stack. Else PAGE_ALIGN it and return back
> @@ -262,3 +292,83 @@ void shstk_release(struct task_struct *tsk)
>         vm_munmap(base, size);
>         set_shstk_base(tsk, 0, 0);
>  }
> +
> +int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *status)
> +{
> +       unsigned long bcfi_status = 0;
> +
> +       if (!cpu_supports_shadow_stack())
> +               return -EINVAL;
> +
> +       /* this means shadow stack is enabled on the task */
> +       bcfi_status |= (is_shstk_enabled(t) ? PR_SHADOW_STACK_ENABLE : 0);
> +
> +       return copy_to_user(status, &bcfi_status, sizeof(bcfi_status)) ? -EFAULT : 0;
> +}
> +
> +int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status)
> +{
> +       unsigned long size = 0, addr = 0;
> +       bool enable_shstk = false;
> +
> +       if (!cpu_supports_shadow_stack())
> +               return -EINVAL;
> +
> +       /* Reject unknown flags */
> +       if (status & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
> +               return -EINVAL;
> +
> +       /* bcfi status is locked and further can't be modified by user */
> +       if (is_shstk_locked(t))
> +               return -EINVAL;
> +
> +       enable_shstk = status & PR_SHADOW_STACK_ENABLE;
> +       /* Request is to enable shadow stack and shadow stack is not enabled already */
> +       if (enable_shstk && !is_shstk_enabled(t)) {
> +               /* shadow stack was allocated and enable request again
> +                * no need to support such usecase and return EINVAL.
> +                */
> +               if (is_shstk_allocated(t))
> +                       return -EINVAL;
> +
> +               size = calc_shstk_size(0);
> +               addr = allocate_shadow_stack(0, size, 0, false);
> +               if (IS_ERR_VALUE(addr))
> +                       return -ENOMEM;
> +               set_shstk_base(t, addr, size);
> +               set_active_shstk(t, addr + size);
> +       }
> +
> +       /*
> +        * If a request to disable shadow stack happens, let's go ahead and release it
> +        * Although, if CLONE_VFORKed child did this, then in that case we will end up
> +        * not releasing the shadow stack (because it might be needed in parent). Although
> +        * we will disable it for VFORKed child. And if VFORKed child tries to enable again
> +        * then in that case, it'll get entirely new shadow stack because following condition
> +        * are true
> +        *  - shadow stack was not enabled for vforked child
> +        *  - shadow stack base was anyways pointing to 0
> +        * This shouldn't be a big issue because we want parent to have availability of shadow
> +        * stack whenever VFORKed child releases resources via exit or exec but at the same
> +        * time we want VFORKed child to break away and establish new shadow stack if it desires
> +        *
> +        */
> +       if (!enable_shstk)
> +               shstk_release(t);
> +
> +       set_shstk_status(t, enable_shstk);
> +       return 0;
> +}
> +
> +int arch_lock_shadow_stack_status(struct task_struct *task,
> +                                 unsigned long arg)
> +{
> +       /* If shtstk not supported or not enabled on task, nothing to lock here */
> +       if (!cpu_supports_shadow_stack() ||
> +           !is_shstk_enabled(task) || arg != 0)
> +               return -EINVAL;
> +
> +       set_shstk_lock(task);
> +
> +       return 0;
> +}
>

LGTM

Reviewed-by: Zong Li <zong.li@sifive.com>

> --
> 2.34.1
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
diff mbox series

Patch

diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h
index 82d28ac98d76..c4dcd256f19a 100644
--- a/arch/riscv/include/asm/usercfi.h
+++ b/arch/riscv/include/asm/usercfi.h
@@ -7,6 +7,7 @@ 
 
 #ifndef __ASSEMBLY__
 #include <linux/types.h>
+#include <linux/prctl.h>
 
 struct task_struct;
 struct kernel_clone_args;
@@ -14,7 +15,8 @@  struct kernel_clone_args;
 #ifdef CONFIG_RISCV_USER_CFI
 struct cfi_status {
 	unsigned long ubcfi_en : 1; /* Enable for backward cfi. */
-	unsigned long rsvd : ((sizeof(unsigned long) * 8) - 1);
+	unsigned long ubcfi_locked : 1;
+	unsigned long rsvd : ((sizeof(unsigned long) * 8) - 2);
 	unsigned long user_shdw_stk; /* Current user shadow stack pointer */
 	unsigned long shdw_stk_base; /* Base address of shadow stack */
 	unsigned long shdw_stk_size; /* size of shadow stack */
@@ -27,6 +29,12 @@  void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, unsigned
 unsigned long get_shstk_base(struct task_struct *task, unsigned long *size);
 void set_active_shstk(struct task_struct *task, unsigned long shstk_addr);
 bool is_shstk_enabled(struct task_struct *task);
+bool is_shstk_locked(struct task_struct *task);
+bool is_shstk_allocated(struct task_struct *task);
+void set_shstk_lock(struct task_struct *task);
+void set_shstk_status(struct task_struct *task, bool enable);
+
+#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK (PR_SHADOW_STACK_ENABLE)
 
 #else
 
@@ -42,6 +50,14 @@  bool is_shstk_enabled(struct task_struct *task);
 
 #define is_shstk_enabled(task) false
 
+#define is_shstk_locked(task) false
+
+#define is_shstk_allocated(task) false
+
+#define set_shstk_lock(task)
+
+#define set_shstk_status(task, enable)
+
 #endif /* CONFIG_RISCV_USER_CFI */
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 99acb6342a37..cd11667593fe 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -153,6 +153,14 @@  void start_thread(struct pt_regs *regs, unsigned long pc,
 	regs->epc = pc;
 	regs->sp = sp;
 
+	/*
+	 * clear shadow stack state on exec.
+	 * libc will set it later via prctl.
+	 */
+	set_shstk_status(current, false);
+	set_shstk_base(current, 0, 0);
+	set_active_shstk(current, 0);
+
 #ifdef CONFIG_64BIT
 	regs->status &= ~SR_UXL;
 
diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
index 73cf87dab186..b93b324eed26 100644
--- a/arch/riscv/kernel/usercfi.c
+++ b/arch/riscv/kernel/usercfi.c
@@ -24,6 +24,16 @@  bool is_shstk_enabled(struct task_struct *task)
 	return task->thread_info.user_cfi_state.ubcfi_en ? true : false;
 }
 
+bool is_shstk_allocated(struct task_struct *task)
+{
+	return task->thread_info.user_cfi_state.shdw_stk_base ? true : false;
+}
+
+bool is_shstk_locked(struct task_struct *task)
+{
+	return task->thread_info.user_cfi_state.ubcfi_locked ? true : false;
+}
+
 void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, unsigned long size)
 {
 	task->thread_info.user_cfi_state.shdw_stk_base = shstk_addr;
@@ -42,6 +52,26 @@  void set_active_shstk(struct task_struct *task, unsigned long shstk_addr)
 	task->thread_info.user_cfi_state.user_shdw_stk = shstk_addr;
 }
 
+void set_shstk_status(struct task_struct *task, bool enable)
+{
+	if (!cpu_supports_shadow_stack())
+		return;
+
+	task->thread_info.user_cfi_state.ubcfi_en = enable ? 1 : 0;
+
+	if (enable)
+		task->thread.envcfg |= ENVCFG_SSE;
+	else
+		task->thread.envcfg &= ~ENVCFG_SSE;
+
+	csr_write(CSR_ENVCFG, task->thread.envcfg);
+}
+
+void set_shstk_lock(struct task_struct *task)
+{
+	task->thread_info.user_cfi_state.ubcfi_locked = 1;
+}
+
 /*
  * If size is 0, then to be compatible with regular stack we want it to be as big as
  * regular stack. Else PAGE_ALIGN it and return back
@@ -262,3 +292,83 @@  void shstk_release(struct task_struct *tsk)
 	vm_munmap(base, size);
 	set_shstk_base(tsk, 0, 0);
 }
+
+int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *status)
+{
+	unsigned long bcfi_status = 0;
+
+	if (!cpu_supports_shadow_stack())
+		return -EINVAL;
+
+	/* this means shadow stack is enabled on the task */
+	bcfi_status |= (is_shstk_enabled(t) ? PR_SHADOW_STACK_ENABLE : 0);
+
+	return copy_to_user(status, &bcfi_status, sizeof(bcfi_status)) ? -EFAULT : 0;
+}
+
+int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status)
+{
+	unsigned long size = 0, addr = 0;
+	bool enable_shstk = false;
+
+	if (!cpu_supports_shadow_stack())
+		return -EINVAL;
+
+	/* Reject unknown flags */
+	if (status & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
+		return -EINVAL;
+
+	/* bcfi status is locked and further can't be modified by user */
+	if (is_shstk_locked(t))
+		return -EINVAL;
+
+	enable_shstk = status & PR_SHADOW_STACK_ENABLE;
+	/* Request is to enable shadow stack and shadow stack is not enabled already */
+	if (enable_shstk && !is_shstk_enabled(t)) {
+		/* shadow stack was allocated and enable request again
+		 * no need to support such usecase and return EINVAL.
+		 */
+		if (is_shstk_allocated(t))
+			return -EINVAL;
+
+		size = calc_shstk_size(0);
+		addr = allocate_shadow_stack(0, size, 0, false);
+		if (IS_ERR_VALUE(addr))
+			return -ENOMEM;
+		set_shstk_base(t, addr, size);
+		set_active_shstk(t, addr + size);
+	}
+
+	/*
+	 * If a request to disable shadow stack happens, let's go ahead and release it
+	 * Although, if CLONE_VFORKed child did this, then in that case we will end up
+	 * not releasing the shadow stack (because it might be needed in parent). Although
+	 * we will disable it for VFORKed child. And if VFORKed child tries to enable again
+	 * then in that case, it'll get entirely new shadow stack because following condition
+	 * are true
+	 *  - shadow stack was not enabled for vforked child
+	 *  - shadow stack base was anyways pointing to 0
+	 * This shouldn't be a big issue because we want parent to have availability of shadow
+	 * stack whenever VFORKed child releases resources via exit or exec but at the same
+	 * time we want VFORKed child to break away and establish new shadow stack if it desires
+	 *
+	 */
+	if (!enable_shstk)
+		shstk_release(t);
+
+	set_shstk_status(t, enable_shstk);
+	return 0;
+}
+
+int arch_lock_shadow_stack_status(struct task_struct *task,
+				  unsigned long arg)
+{
+	/* If shtstk not supported or not enabled on task, nothing to lock here */
+	if (!cpu_supports_shadow_stack() ||
+	    !is_shstk_enabled(task) || arg != 0)
+		return -EINVAL;
+
+	set_shstk_lock(task);
+
+	return 0;
+}