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Peter Anvin" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , Paul Walmsley , Palmer Dabbelt , Albert Ou , Conor Dooley , Rob Herring , Krzysztof Kozlowski , Arnd Bergmann , Christian Brauner , Peter Zijlstra , Oleg Nesterov , Eric Biederman , Kees Cook , Jonathan Corbet , Shuah Khan , Jann Horn , Conor Dooley , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, alistair.francis@wdc.com, richard.henderson@linaro.org, jim.shu@sifive.com, andybnac@gmail.com, kito.cheng@sifive.com, charlie@rivosinc.com, atishp@rivosinc.com, evan@rivosinc.com, cleger@rivosinc.com, alexghiti@rivosinc.com, samitolvanen@google.com, broonie@kernel.org, rick.p.edgecombe@intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, Mar 10, 2025 at 11:42=E2=80=AFPM 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 stac= k > 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/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/as= m/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_st= ruct *mm) > } > #endif > > +#define deactivate_mm deactivate_mm > +static inline void deactivate_mm(struct task_struct *tsk, > + struct mm_struct *mm) > +{ > + shstk_release(tsk); > +} > + > #include > > #endif /* _ASM_RISCV_MMU_CONTEXT_H */ > diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/us= ercfi.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 > > +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 *ar= gs); > +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 *si= ze); > +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 > #include > #include > +#include > > #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER= _TASK) > #include > @@ -211,6 +212,7 @@ int copy_thread(struct task_struct *p, const struct k= ernel_clone_args *args) > unsigned long clone_flags =3D args->flags; > unsigned long usp =3D args->stack; > unsigned long tls =3D args->tls; > + unsigned long ssp =3D 0; > struct pt_regs *childregs =3D task_pt_regs(p); > > /* Ensure all threads in this mm have the same pointer masking mo= de. */ > @@ -229,11 +231,18 @@ int copy_thread(struct task_struct *p, const struct= kernel_clone_args *args) > p->thread.s[0] =3D (unsigned long)args->fn; > p->thread.s[1] =3D (unsigned long)args->fn_arg; > } else { > + /* allocate new shadow stack if needed. In case of CLONE_= VM we have to */ > + ssp =3D shstk_alloc_thread_stack(p, args); > + if (IS_ERR_VALUE(ssp)) > + return PTR_ERR((void *)ssp); > + > *childregs =3D *(current_pt_regs()); > /* Turn off status.VS */ > riscv_v_vstate_off(childregs); > if (usp) /* User fork */ > childregs->sp =3D usp; > + /* if needed, set new ssp */ > + ssp ? set_active_shstk(p, ssp) : 0; > if (clone_flags & CLONE_SETTLS) > childregs->tp =3D tls; > childregs->a0 =3D 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 =3D shstk_addr; > + task->thread_info.user_cfi_state.shdw_stk_size =3D size; > +} > + > +unsigned long get_shstk_base(struct task_struct *task, unsigned long *si= ze) > +{ > + if (size) > + *size =3D 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 =3D 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, add= r, 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 speci= fied 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 i= f 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 *ar= gs) > +{ > + 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 =3D 0 and size =3D 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 separat= e shadow > + * stack is needed for new cloned thread. Note: below allocation = is happening > + * using current mm. > + */ > + size =3D calc_shstk_size(args->stack_size); > + addr =3D 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 =3D 0, size =3D 0; > + /* If shadow stack is not supported or not enabled, nothing to re= lease */ > + 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 shar= e > + * the same mm struct. Move forward only when they're same. > + */ > + if (!tsk->mm || tsk->mm !=3D 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 =3D get_shstk_base(tsk, &size); > + if (!base) > + return; > + > + vm_munmap(base, size); > + set_shstk_base(tsk, 0, 0); > +} > LGTM. Reviewed-by: Zong Li > -- > 2.34.1 > > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv