| Message ID | 20250314-v5_user_cfi_series-v12-11-e51202b53138@rivosinc.com |
|---|---|
| State | New |
| Headers | show |
| Series | riscv control-flow integrity for usermode | expand |
On 14/03/2025 22:39, Deepak Gupta wrote: > Userspace specifies CLONE_VM to share address space and spawn new thread. > `clone` allow userspace to specify a new stack for new thread. However > there is no way to specify new shadow stack base address without changing > API. This patch allocates a new shadow stack whenever CLONE_VM is given. > > In case of CLONE_VFORK, parent is suspended until child finishes and thus > can child use parent shadow stack. In case of !CLONE_VM, COW kicks in > because entire address space is copied from parent to child. > > `clone3` is extensible and can provide mechanisms using which shadow stack > as an input parameter can be provided. This is not settled yet and being > extensively discussed on mailing list. Once that's settled, this commit > will adapt to that. What's the status of this discussion? Can you provide a Link to it? > > Reviewed-by: Zong Li <zong.li@sifive.com> > Signed-off-by: Deepak Gupta <debug@rivosinc.com> > --- > arch/riscv/include/asm/mmu_context.h | 7 ++ > arch/riscv/include/asm/usercfi.h | 25 ++++++++ > arch/riscv/kernel/process.c | 9 +++ > arch/riscv/kernel/usercfi.c | 120 +++++++++++++++++++++++++++++++++++ > 4 files changed, 161 insertions(+) > > diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h > index 8c4bc49a3a0f..dbf27a78df6c 100644 > --- a/arch/riscv/include/asm/mmu_context.h > +++ b/arch/riscv/include/asm/mmu_context.h > @@ -48,6 +48,13 @@ static inline unsigned long mm_untag_mask(struct mm_struct *mm) > } > #endif > > +#define deactivate_mm deactivate_mm > +static inline void deactivate_mm(struct task_struct *tsk, > + struct mm_struct *mm) > +{ > + shstk_release(tsk); > +} > + > #include <asm-generic/mmu_context.h> > > #endif /* _ASM_RISCV_MMU_CONTEXT_H */ > diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h > index 5f2027c51917..82d28ac98d76 100644 > --- a/arch/riscv/include/asm/usercfi.h > +++ b/arch/riscv/include/asm/usercfi.h > @@ -8,6 +8,9 @@ > #ifndef __ASSEMBLY__ > #include <linux/types.h> > > +struct task_struct; > +struct kernel_clone_args; > + > #ifdef CONFIG_RISCV_USER_CFI > struct cfi_status { > unsigned long ubcfi_en : 1; /* Enable for backward cfi. */ > @@ -17,6 +20,28 @@ struct cfi_status { > unsigned long shdw_stk_size; /* size of shadow stack */ > }; > > +unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, > + const struct kernel_clone_args *args); > +void shstk_release(struct task_struct *tsk); > +void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, unsigned long size); > +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); > + > +#else > + > +#define shstk_alloc_thread_stack(tsk, args) 0 > + > +#define shstk_release(tsk) > + > +#define get_shstk_base(task, size) 0UL > + > +#define set_shstk_base(task, shstk_addr, size) > + > +#define set_active_shstk(task, shstk_addr) > + > +#define is_shstk_enabled(task) false > + > #endif /* CONFIG_RISCV_USER_CFI */ > > #endif /* __ASSEMBLY__ */ > diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c > index 7c244de77180..99acb6342a37 100644 > --- a/arch/riscv/kernel/process.c > +++ b/arch/riscv/kernel/process.c > @@ -29,6 +29,7 @@ > #include <asm/vector.h> > #include <asm/cpufeature.h> > #include <asm/exec.h> > +#include <asm/usercfi.h> > > #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK) > #include <linux/stackprotector.h> > @@ -211,6 +212,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) > unsigned long clone_flags = args->flags; > unsigned long usp = args->stack; > unsigned long tls = args->tls; > + unsigned long ssp = 0; > struct pt_regs *childregs = task_pt_regs(p); > > /* Ensure all threads in this mm have the same pointer masking mode. */ > @@ -229,11 +231,18 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) > p->thread.s[0] = (unsigned long)args->fn; > p->thread.s[1] = (unsigned long)args->fn_arg; > } else { > + /* allocate new shadow stack if needed. In case of CLONE_VM we have to */ > + ssp = shstk_alloc_thread_stack(p, args); > + if (IS_ERR_VALUE(ssp)) > + return PTR_ERR((void *)ssp); > + > *childregs = *(current_pt_regs()); > /* Turn off status.VS */ > riscv_v_vstate_off(childregs); > if (usp) /* User fork */ > childregs->sp = usp; > + /* if needed, set new ssp */ > + ssp ? set_active_shstk(p, ssp) : 0; The use of the ternary here is weird, can you change that to a if statement? > if (clone_flags & CLONE_SETTLS) > childregs->tp = tls; > childregs->a0 = 0; /* Return value of fork() */ > diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c > index 24022809a7b5..73cf87dab186 100644 > --- a/arch/riscv/kernel/usercfi.c > +++ b/arch/riscv/kernel/usercfi.c > @@ -19,6 +19,41 @@ > > #define SHSTK_ENTRY_SIZE sizeof(void *) > > +bool is_shstk_enabled(struct task_struct *task) > +{ > + return task->thread_info.user_cfi_state.ubcfi_en ? 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; > + task->thread_info.user_cfi_state.shdw_stk_size = size; > +} > + > +unsigned long get_shstk_base(struct task_struct *task, unsigned long *size) > +{ > + if (size) > + *size = task->thread_info.user_cfi_state.shdw_stk_size; > + return task->thread_info.user_cfi_state.shdw_stk_base; > +} > + > +void set_active_shstk(struct task_struct *task, unsigned long shstk_addr) > +{ > + task->thread_info.user_cfi_state.user_shdw_stk = shstk_addr; > +} > + > +/* > + * 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 > + */ > +static unsigned long calc_shstk_size(unsigned long size) > +{ > + if (size) > + return PAGE_ALIGN(size); > + > + return PAGE_ALIGN(min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G)); > +} > + > /* > * Writes on shadow stack can either be `sspush` or `ssamoswap`. `sspush` can happen > * implicitly on current shadow stack pointed to by CSR_SSP. `ssamoswap` takes pointer to > @@ -142,3 +177,88 @@ SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsi > > return allocate_shadow_stack(addr, aligned_size, size, set_tok); > } > + > +/* > + * This gets called during clone/clone3/fork. And is needed to allocate a shadow stack for > + * cases where CLONE_VM is specified and thus a different stack is specified by user. We > + * thus need a separate shadow stack too. How does separate shadow stack is specified by > + * user is still being debated. Once that's settled, remove this part of the comment. > + * This function simply returns 0 if shadow stack are not supported or if separate shadow > + * stack allocation is not needed (like in case of !CLONE_VM) > + */ > +unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, > + const struct kernel_clone_args *args) > +{ > + unsigned long addr, size; > + > + /* If shadow stack is not supported, return 0 */ > + if (!cpu_supports_shadow_stack()) > + return 0; > + > + /* > + * If shadow stack is not enabled on the new thread, skip any > + * switch to a new shadow stack. > + */ > + if (!is_shstk_enabled(tsk)) > + return 0; > + > + /* > + * For CLONE_VFORK the child will share the parents shadow stack. > + * Set base = 0 and size = 0, this is special means to track this state > + * so the freeing logic run for child knows to leave it alone. > + */ > + if (args->flags & CLONE_VFORK) { > + set_shstk_base(tsk, 0, 0); > + return 0; > + } > + > + /* > + * For !CLONE_VM the child will use a copy of the parents shadow > + * stack. > + */ > + if (!(args->flags & CLONE_VM)) > + return 0; > + > + /* > + * reaching here means, CLONE_VM was specified and thus a separate shadow > + * stack is needed for new cloned thread. Note: below allocation is happening > + * using current mm. > + */ > + size = calc_shstk_size(args->stack_size); > + addr = allocate_shadow_stack(0, size, 0, false); > + if (IS_ERR_VALUE(addr)) > + return addr; > + > + set_shstk_base(tsk, addr, size); > + > + return addr + size; > +} > + > +void shstk_release(struct task_struct *tsk) > +{ > + unsigned long base = 0, size = 0; > + /* If shadow stack is not supported or not enabled, nothing to release */ > + if (!cpu_supports_shadow_stack() || !is_shstk_enabled(tsk)) > + return; > + > + /* > + * When fork() with CLONE_VM fails, the child (tsk) already has a > + * shadow stack allocated, and exit_thread() calls this function to > + * free it. In this case the parent (current) and the child share > + * the same mm struct. Move forward only when they're same. > + */ > + if (!tsk->mm || tsk->mm != current->mm) > + return; > + > + /* > + * We know shadow stack is enabled but if base is NULL, then > + * this task is not managing its own shadow stack (CLONE_VFORK). So > + * skip freeing it. > + */ > + base = get_shstk_base(tsk, &size); > + if (!base) > + return; > + > + vm_munmap(base, size); > + set_shstk_base(tsk, 0, 0); > +} >
On Tue, Apr 08, 2025 at 12:51:45PM +0200, Alexandre Ghiti wrote: > >On 14/03/2025 22:39, Deepak Gupta wrote: >>Userspace specifies CLONE_VM to share address space and spawn new thread. >>`clone` allow userspace to specify a new stack for new thread. However >>there is no way to specify new shadow stack base address without changing >>API. This patch allocates a new shadow stack whenever CLONE_VM is given. >> >>In case of CLONE_VFORK, parent is suspended until child finishes and thus >>can child use parent shadow stack. In case of !CLONE_VM, COW kicks in >>because entire address space is copied from parent to child. >> >>`clone3` is extensible and can provide mechanisms using which shadow stack >>as an input parameter can be provided. This is not settled yet and being >>extensively discussed on mailing list. Once that's settled, this commit >>will adapt to that. > > >What's the status of this discussion? Can you provide a Link to it? It's ongoing right now at v15 https://lore.kernel.org/all/20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@kernel.org/ > > >> >>Reviewed-by: Zong Li <zong.li@sifive.com> >>Signed-off-by: Deepak Gupta <debug@rivosinc.com> >>--- >> arch/riscv/include/asm/mmu_context.h | 7 ++ >> arch/riscv/include/asm/usercfi.h | 25 ++++++++ >> arch/riscv/kernel/process.c | 9 +++ >> arch/riscv/kernel/usercfi.c | 120 +++++++++++++++++++++++++++++++++++ >> 4 files changed, 161 insertions(+) >> >>diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h >>index 8c4bc49a3a0f..dbf27a78df6c 100644 >>--- a/arch/riscv/include/asm/mmu_context.h >>+++ b/arch/riscv/include/asm/mmu_context.h >>@@ -48,6 +48,13 @@ static inline unsigned long mm_untag_mask(struct mm_struct *mm) >> } >> #endif >>+#define deactivate_mm deactivate_mm >>+static inline void deactivate_mm(struct task_struct *tsk, >>+ struct mm_struct *mm) >>+{ >>+ shstk_release(tsk); >>+} >>+ >> #include <asm-generic/mmu_context.h> >> #endif /* _ASM_RISCV_MMU_CONTEXT_H */ >>diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h >>index 5f2027c51917..82d28ac98d76 100644 >>--- a/arch/riscv/include/asm/usercfi.h >>+++ b/arch/riscv/include/asm/usercfi.h >>@@ -8,6 +8,9 @@ >> #ifndef __ASSEMBLY__ >> #include <linux/types.h> >>+struct task_struct; >>+struct kernel_clone_args; >>+ >> #ifdef CONFIG_RISCV_USER_CFI >> struct cfi_status { >> unsigned long ubcfi_en : 1; /* Enable for backward cfi. */ >>@@ -17,6 +20,28 @@ struct cfi_status { >> unsigned long shdw_stk_size; /* size of shadow stack */ >> }; >>+unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, >>+ const struct kernel_clone_args *args); >>+void shstk_release(struct task_struct *tsk); >>+void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, unsigned long size); >>+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); >>+ >>+#else >>+ >>+#define shstk_alloc_thread_stack(tsk, args) 0 >>+ >>+#define shstk_release(tsk) >>+ >>+#define get_shstk_base(task, size) 0UL >>+ >>+#define set_shstk_base(task, shstk_addr, size) >>+ >>+#define set_active_shstk(task, shstk_addr) >>+ >>+#define is_shstk_enabled(task) false >>+ >> #endif /* CONFIG_RISCV_USER_CFI */ >> #endif /* __ASSEMBLY__ */ >>diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c >>index 7c244de77180..99acb6342a37 100644 >>--- a/arch/riscv/kernel/process.c >>+++ b/arch/riscv/kernel/process.c >>@@ -29,6 +29,7 @@ >> #include <asm/vector.h> >> #include <asm/cpufeature.h> >> #include <asm/exec.h> >>+#include <asm/usercfi.h> >> #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK) >> #include <linux/stackprotector.h> >>@@ -211,6 +212,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) >> unsigned long clone_flags = args->flags; >> unsigned long usp = args->stack; >> unsigned long tls = args->tls; >>+ unsigned long ssp = 0; >> struct pt_regs *childregs = task_pt_regs(p); >> /* Ensure all threads in this mm have the same pointer masking mode. */ >>@@ -229,11 +231,18 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) >> p->thread.s[0] = (unsigned long)args->fn; >> p->thread.s[1] = (unsigned long)args->fn_arg; >> } else { >>+ /* allocate new shadow stack if needed. In case of CLONE_VM we have to */ >>+ ssp = shstk_alloc_thread_stack(p, args); >>+ if (IS_ERR_VALUE(ssp)) >>+ return PTR_ERR((void *)ssp); >>+ >> *childregs = *(current_pt_regs()); >> /* Turn off status.VS */ >> riscv_v_vstate_off(childregs); >> if (usp) /* User fork */ >> childregs->sp = usp; >>+ /* if needed, set new ssp */ >>+ ssp ? set_active_shstk(p, ssp) : 0; > > >The use of the ternary here is weird, can you change that to a if >statement? > > >> if (clone_flags & CLONE_SETTLS) >> childregs->tp = tls; >> childregs->a0 = 0; /* Return value of fork() */ >>diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c >>index 24022809a7b5..73cf87dab186 100644 >>--- a/arch/riscv/kernel/usercfi.c >>+++ b/arch/riscv/kernel/usercfi.c >>@@ -19,6 +19,41 @@ >> #define SHSTK_ENTRY_SIZE sizeof(void *) >>+bool is_shstk_enabled(struct task_struct *task) >>+{ >>+ return task->thread_info.user_cfi_state.ubcfi_en ? 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; >>+ task->thread_info.user_cfi_state.shdw_stk_size = size; >>+} >>+ >>+unsigned long get_shstk_base(struct task_struct *task, unsigned long *size) >>+{ >>+ if (size) >>+ *size = task->thread_info.user_cfi_state.shdw_stk_size; >>+ return task->thread_info.user_cfi_state.shdw_stk_base; >>+} >>+ >>+void set_active_shstk(struct task_struct *task, unsigned long shstk_addr) >>+{ >>+ task->thread_info.user_cfi_state.user_shdw_stk = shstk_addr; >>+} >>+ >>+/* >>+ * 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 >>+ */ >>+static unsigned long calc_shstk_size(unsigned long size) >>+{ >>+ if (size) >>+ return PAGE_ALIGN(size); >>+ >>+ return PAGE_ALIGN(min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G)); >>+} >>+ >> /* >> * Writes on shadow stack can either be `sspush` or `ssamoswap`. `sspush` can happen >> * implicitly on current shadow stack pointed to by CSR_SSP. `ssamoswap` takes pointer to >>@@ -142,3 +177,88 @@ SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsi >> return allocate_shadow_stack(addr, aligned_size, size, set_tok); >> } >>+ >>+/* >>+ * This gets called during clone/clone3/fork. And is needed to allocate a shadow stack for >>+ * cases where CLONE_VM is specified and thus a different stack is specified by user. We >>+ * thus need a separate shadow stack too. How does separate shadow stack is specified by >>+ * user is still being debated. Once that's settled, remove this part of the comment. >>+ * This function simply returns 0 if shadow stack are not supported or if separate shadow >>+ * stack allocation is not needed (like in case of !CLONE_VM) >>+ */ >>+unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, >>+ const struct kernel_clone_args *args) >>+{ >>+ unsigned long addr, size; >>+ >>+ /* If shadow stack is not supported, return 0 */ >>+ if (!cpu_supports_shadow_stack()) >>+ return 0; >>+ >>+ /* >>+ * If shadow stack is not enabled on the new thread, skip any >>+ * switch to a new shadow stack. >>+ */ >>+ if (!is_shstk_enabled(tsk)) >>+ return 0; >>+ >>+ /* >>+ * For CLONE_VFORK the child will share the parents shadow stack. >>+ * Set base = 0 and size = 0, this is special means to track this state >>+ * so the freeing logic run for child knows to leave it alone. >>+ */ >>+ if (args->flags & CLONE_VFORK) { >>+ set_shstk_base(tsk, 0, 0); >>+ return 0; >>+ } >>+ >>+ /* >>+ * For !CLONE_VM the child will use a copy of the parents shadow >>+ * stack. >>+ */ >>+ if (!(args->flags & CLONE_VM)) >>+ return 0; >>+ >>+ /* >>+ * reaching here means, CLONE_VM was specified and thus a separate shadow >>+ * stack is needed for new cloned thread. Note: below allocation is happening >>+ * using current mm. >>+ */ >>+ size = calc_shstk_size(args->stack_size); >>+ addr = allocate_shadow_stack(0, size, 0, false); >>+ if (IS_ERR_VALUE(addr)) >>+ return addr; >>+ >>+ set_shstk_base(tsk, addr, size); >>+ >>+ return addr + size; >>+} >>+ >>+void shstk_release(struct task_struct *tsk) >>+{ >>+ unsigned long base = 0, size = 0; >>+ /* If shadow stack is not supported or not enabled, nothing to release */ >>+ if (!cpu_supports_shadow_stack() || !is_shstk_enabled(tsk)) >>+ return; >>+ >>+ /* >>+ * When fork() with CLONE_VM fails, the child (tsk) already has a >>+ * shadow stack allocated, and exit_thread() calls this function to >>+ * free it. In this case the parent (current) and the child share >>+ * the same mm struct. Move forward only when they're same. >>+ */ >>+ if (!tsk->mm || tsk->mm != current->mm) >>+ return; >>+ >>+ /* >>+ * We know shadow stack is enabled but if base is NULL, then >>+ * this task is not managing its own shadow stack (CLONE_VFORK). So >>+ * skip freeing it. >>+ */ >>+ base = get_shstk_base(tsk, &size); >>+ if (!base) >>+ return; >>+ >>+ vm_munmap(base, size); >>+ set_shstk_base(tsk, 0, 0); >>+} >>
diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h index 8c4bc49a3a0f..dbf27a78df6c 100644 --- a/arch/riscv/include/asm/mmu_context.h +++ b/arch/riscv/include/asm/mmu_context.h @@ -48,6 +48,13 @@ static inline unsigned long mm_untag_mask(struct mm_struct *mm) } #endif +#define deactivate_mm deactivate_mm +static inline void deactivate_mm(struct task_struct *tsk, + struct mm_struct *mm) +{ + shstk_release(tsk); +} + #include <asm-generic/mmu_context.h> #endif /* _ASM_RISCV_MMU_CONTEXT_H */ diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h index 5f2027c51917..82d28ac98d76 100644 --- a/arch/riscv/include/asm/usercfi.h +++ b/arch/riscv/include/asm/usercfi.h @@ -8,6 +8,9 @@ #ifndef __ASSEMBLY__ #include <linux/types.h> +struct task_struct; +struct kernel_clone_args; + #ifdef CONFIG_RISCV_USER_CFI struct cfi_status { unsigned long ubcfi_en : 1; /* Enable for backward cfi. */ @@ -17,6 +20,28 @@ struct cfi_status { unsigned long shdw_stk_size; /* size of shadow stack */ }; +unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, + const struct kernel_clone_args *args); +void shstk_release(struct task_struct *tsk); +void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, unsigned long size); +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); + +#else + +#define shstk_alloc_thread_stack(tsk, args) 0 + +#define shstk_release(tsk) + +#define get_shstk_base(task, size) 0UL + +#define set_shstk_base(task, shstk_addr, size) + +#define set_active_shstk(task, shstk_addr) + +#define is_shstk_enabled(task) false + #endif /* CONFIG_RISCV_USER_CFI */ #endif /* __ASSEMBLY__ */ diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index 7c244de77180..99acb6342a37 100644 --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -29,6 +29,7 @@ #include <asm/vector.h> #include <asm/cpufeature.h> #include <asm/exec.h> +#include <asm/usercfi.h> #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK) #include <linux/stackprotector.h> @@ -211,6 +212,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) unsigned long clone_flags = args->flags; unsigned long usp = args->stack; unsigned long tls = args->tls; + unsigned long ssp = 0; struct pt_regs *childregs = task_pt_regs(p); /* Ensure all threads in this mm have the same pointer masking mode. */ @@ -229,11 +231,18 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) p->thread.s[0] = (unsigned long)args->fn; p->thread.s[1] = (unsigned long)args->fn_arg; } else { + /* allocate new shadow stack if needed. In case of CLONE_VM we have to */ + ssp = shstk_alloc_thread_stack(p, args); + if (IS_ERR_VALUE(ssp)) + return PTR_ERR((void *)ssp); + *childregs = *(current_pt_regs()); /* Turn off status.VS */ riscv_v_vstate_off(childregs); if (usp) /* User fork */ childregs->sp = usp; + /* if needed, set new ssp */ + ssp ? set_active_shstk(p, ssp) : 0; if (clone_flags & CLONE_SETTLS) childregs->tp = tls; childregs->a0 = 0; /* Return value of fork() */ diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c index 24022809a7b5..73cf87dab186 100644 --- a/arch/riscv/kernel/usercfi.c +++ b/arch/riscv/kernel/usercfi.c @@ -19,6 +19,41 @@ #define SHSTK_ENTRY_SIZE sizeof(void *) +bool is_shstk_enabled(struct task_struct *task) +{ + return task->thread_info.user_cfi_state.ubcfi_en ? 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; + task->thread_info.user_cfi_state.shdw_stk_size = size; +} + +unsigned long get_shstk_base(struct task_struct *task, unsigned long *size) +{ + if (size) + *size = task->thread_info.user_cfi_state.shdw_stk_size; + return task->thread_info.user_cfi_state.shdw_stk_base; +} + +void set_active_shstk(struct task_struct *task, unsigned long shstk_addr) +{ + task->thread_info.user_cfi_state.user_shdw_stk = shstk_addr; +} + +/* + * 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 + */ +static unsigned long calc_shstk_size(unsigned long size) +{ + if (size) + return PAGE_ALIGN(size); + + return PAGE_ALIGN(min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G)); +} + /* * Writes on shadow stack can either be `sspush` or `ssamoswap`. `sspush` can happen * implicitly on current shadow stack pointed to by CSR_SSP. `ssamoswap` takes pointer to @@ -142,3 +177,88 @@ SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsi return allocate_shadow_stack(addr, aligned_size, size, set_tok); } + +/* + * This gets called during clone/clone3/fork. And is needed to allocate a shadow stack for + * cases where CLONE_VM is specified and thus a different stack is specified by user. We + * thus need a separate shadow stack too. How does separate shadow stack is specified by + * user is still being debated. Once that's settled, remove this part of the comment. + * This function simply returns 0 if shadow stack are not supported or if separate shadow + * stack allocation is not needed (like in case of !CLONE_VM) + */ +unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, + const struct kernel_clone_args *args) +{ + unsigned long addr, size; + + /* If shadow stack is not supported, return 0 */ + if (!cpu_supports_shadow_stack()) + return 0; + + /* + * If shadow stack is not enabled on the new thread, skip any + * switch to a new shadow stack. + */ + if (!is_shstk_enabled(tsk)) + return 0; + + /* + * For CLONE_VFORK the child will share the parents shadow stack. + * Set base = 0 and size = 0, this is special means to track this state + * so the freeing logic run for child knows to leave it alone. + */ + if (args->flags & CLONE_VFORK) { + set_shstk_base(tsk, 0, 0); + return 0; + } + + /* + * For !CLONE_VM the child will use a copy of the parents shadow + * stack. + */ + if (!(args->flags & CLONE_VM)) + return 0; + + /* + * reaching here means, CLONE_VM was specified and thus a separate shadow + * stack is needed for new cloned thread. Note: below allocation is happening + * using current mm. + */ + size = calc_shstk_size(args->stack_size); + addr = allocate_shadow_stack(0, size, 0, false); + if (IS_ERR_VALUE(addr)) + return addr; + + set_shstk_base(tsk, addr, size); + + return addr + size; +} + +void shstk_release(struct task_struct *tsk) +{ + unsigned long base = 0, size = 0; + /* If shadow stack is not supported or not enabled, nothing to release */ + if (!cpu_supports_shadow_stack() || !is_shstk_enabled(tsk)) + return; + + /* + * When fork() with CLONE_VM fails, the child (tsk) already has a + * shadow stack allocated, and exit_thread() calls this function to + * free it. In this case the parent (current) and the child share + * the same mm struct. Move forward only when they're same. + */ + if (!tsk->mm || tsk->mm != current->mm) + return; + + /* + * We know shadow stack is enabled but if base is NULL, then + * this task is not managing its own shadow stack (CLONE_VFORK). So + * skip freeing it. + */ + base = get_shstk_base(tsk, &size); + if (!base) + return; + + vm_munmap(base, size); + set_shstk_base(tsk, 0, 0); +}