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charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <5f66b425-679a-4f1f-9ca1-0c0bf3950a0a@ghiti.fr> X-Rspamd-Queue-Id: 8085B4001E X-Stat-Signature: z98n1saq17b8887e6xu5w8mud3o8obhh X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1715620228-125547 X-HE-Meta: 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 Z+NsO/J1 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, May 12, 2024 at 07:05:27PM +0200, Alexandre Ghiti wrote: >On 04/04/2024 01:35, Deepak Gupta wrote: >>Userspace specifies VM_CLONE to share address space and spawn new thread. > > >CLONE_VM? Yes I meant CLONE_VM, will fix it. > > >>`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 VM_CLONE is given. >> >>In case of VM_FORK, parent is suspended until child finishes and thus can > > >You mean CLONE_VFORK here right? Yes I meant CLONE_VFORK, will fix it. > > >>child use parent shadow stack. In case of !VM_CLONE, 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. >> >>Signed-off-by: Deepak Gupta >>--- >> arch/riscv/include/asm/usercfi.h | 39 ++++++++++ >> arch/riscv/kernel/process.c | 12 ++- >> arch/riscv/kernel/usercfi.c | 121 +++++++++++++++++++++++++++++++ >> 3 files changed, 171 insertions(+), 1 deletion(-) >> >>diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h >>index 4fa201b4fc4e..b47574a7a8c9 100644 >>--- a/arch/riscv/include/asm/usercfi.h >>+++ b/arch/riscv/include/asm/usercfi.h >>@@ -8,6 +8,9 @@ >> #ifndef __ASSEMBLY__ >> #include >>+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 +20,42 @@ 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); >>+void set_active_shstk(struct task_struct *task, unsigned long shstk_addr); >>+bool is_shstk_enabled(struct task_struct *task); >>+ >>+#else >>+ >>+static inline unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, >>+ const struct kernel_clone_args *args) >>+{ >>+ return 0; >>+} >>+ >>+static inline void shstk_release(struct task_struct *tsk) >>+{ >>+ >>+} >>+ >>+static inline void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, >>+ unsigned long size) >>+{ >>+ >>+} >>+ >>+static inline void set_active_shstk(struct task_struct *task, unsigned long shstk_addr) >>+{ >>+ >>+} >>+ >>+static inline bool is_shstk_enabled(struct task_struct *task) >>+{ >>+ return false; >>+} >>+ >> #endif /* CONFIG_RISCV_USER_CFI */ >> #endif /* __ASSEMBLY__ */ >>diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c >>index ce577cdc2af3..ef48a25b0eff 100644 >>--- a/arch/riscv/kernel/process.c >>+++ b/arch/riscv/kernel/process.c >>@@ -26,6 +26,7 @@ >> #include >> #include >> #include >>+#include >> register unsigned long gp_in_global __asm__("gp"); >>@@ -202,7 +203,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) >> void exit_thread(struct task_struct *tsk) >> { >>- >>+ if (IS_ENABLED(CONFIG_RISCV_USER_CFI)) >>+ shstk_release(tsk); >> } >> int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) >>@@ -210,6 +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); >> memset(&p->thread.s, 0, sizeof(p->thread.s)); >>@@ -225,11 +228,18 @@ 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 (ssp) /* if needed, set new ssp */ >>+ set_active_shstk(p, ssp); >> 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 c4ed0d4e33d6..11ef7ab925c9 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 >>@@ -147,3 +182,89 @@ 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); >>+}