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[2620:137:e000::1:20]) by mx.google.com with ESMTP id bg4-20020a1709028e8400b0019aba699d56si11022754plb.608.2023.03.20.09.53.15; Mon, 20 Mar 2023 09:53:28 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b=iMPS4Njm; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232123AbjCTQrB (ORCPT + 99 others); Mon, 20 Mar 2023 12:47:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40434 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231925AbjCTQpg (ORCPT ); Mon, 20 Mar 2023 12:45:36 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 490DE3345A; Mon, 20 Mar 2023 09:40:23 -0700 (PDT) Date: Mon, 20 Mar 2023 16:39:23 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1679330363; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=n+AhB5DVmRJ5/SesnD9Uq//7BY04ViX2UCS7lKScAbk=; b=iMPS4Njm6cuM1adiLv5HT9e9Y6P/miFkL96eHMaU546MttCTlYSeUJs+nNZ4uc5+JmcAYz dQRAm14baL6383OW69wVaLJvg+PNBy8ozpe/AF4NtGa8LSUo0r4XKltCYjMyksHNcVMZee lyXJCP3cMB7Adp9xDBWW560degju0Z0/D9rYKPoC1sEyPF3iRjxLoDKrU/rwq362TbXuDq Q+Hmuo3KXql+IjPBMxWIz468R+FArUHwg97l9MAjWL9jiPxK0smAfA2XoOkqcv2DfgdyQW +9WL1PTakH+vmOk1poltTNP/MuVn1nOFwh2bmmbBkzh/CD6TGpc4XdNcVIivkw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1679330363; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=n+AhB5DVmRJ5/SesnD9Uq//7BY04ViX2UCS7lKScAbk=; b=CUNRSaxP47GY7x/PbYD2P8BWgWMg5Ayyx1CnKDk/duZGwJ2Q9XvR6bV6EZ7lhlCRkWEacu kRI71vtV/oVkvbBQ== From: "tip-bot2 for Rick Edgecombe" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/shstk] x86/shstk: Handle thread shadow stack Cc: Thomas Gleixner , "Yu-cheng Yu" , Rick Edgecombe , Dave Hansen , "Borislav Petkov (AMD)" , Kees Cook , "Mike Rapoport (IBM)" , Pengfei Xu , John Allen , x86@kernel.org, linux-kernel@vger.kernel.org MIME-Version: 1.0 Message-ID: <167933036316.5837.10138463236733204919.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1760906401342154402?= X-GMAIL-MSGID: =?utf-8?q?1760906401342154402?= The following commit has been merged into the x86/shstk branch of tip: Commit-ID: 2445a5c30aea02788c2444bb96363352abdea687 Gitweb: https://git.kernel.org/tip/2445a5c30aea02788c2444bb96363352abdea687 Author: Rick Edgecombe AuthorDate: Sat, 18 Mar 2023 17:15:25 -07:00 Committer: Dave Hansen CommitterDate: Mon, 20 Mar 2023 09:01:11 -07:00 x86/shstk: Handle thread shadow stack When a process is duplicated, but the child shares the address space with the parent, there is potential for the threads sharing a single stack to cause conflicts for each other. In the normal non-CET case this is handled in two ways. With regular CLONE_VM a new stack is provided by userspace such that the parent and child have different stacks. For vfork, the parent is suspended until the child exits. So as long as the child doesn't return from the vfork()/CLONE_VFORK calling function and sticks to a limited set of operations, the parent and child can share the same stack. For shadow stack, these scenarios present similar sharing problems. For the CLONE_VM case, the child and the parent must have separate shadow stacks. Instead of changing clone to take a shadow stack, have the kernel just allocate one and switch to it. Use stack_size passed from clone3() syscall for thread shadow stack size. A compat-mode thread shadow stack size is further reduced to 1/4. This allows more threads to run in a 32-bit address space. The clone() does not pass stack_size, which was added to clone3(). In that case, use RLIMIT_STACK size and cap to 4 GB. For shadow stack enabled vfork(), the parent and child can share the same shadow stack, like they can share a normal stack. Since the parent is suspended until the child terminates, the child will not interfere with the parent while executing as long as it doesn't return from the vfork() and overwrite up the shadow stack. The child can safely overwrite down the shadow stack, as the parent can just overwrite this later. So CET does not add any additional limitations for vfork(). Free the shadow stack on thread exit by doing it in mm_release(). Skip this when exiting a vfork() child since the stack is shared in the parent. During this operation, the shadow stack pointer of the new thread needs to be updated to point to the newly allocated shadow stack. Since the ability to do this is confined to the FPU subsystem, change fpu_clone() to take the new shadow stack pointer, and update it internally inside the FPU subsystem. This part was suggested by Thomas Gleixner. Co-developed-by: Yu-cheng Yu Suggested-by: Thomas Gleixner Signed-off-by: Yu-cheng Yu Signed-off-by: Rick Edgecombe Signed-off-by: Dave Hansen Reviewed-by: Borislav Petkov (AMD) Reviewed-by: Kees Cook Acked-by: Mike Rapoport (IBM) Tested-by: Pengfei Xu Tested-by: John Allen Tested-by: Kees Cook Link: https://lore.kernel.org/all/20230319001535.23210-31-rick.p.edgecombe%40intel.com --- arch/x86/include/asm/fpu/sched.h | 3 +- arch/x86/include/asm/mmu_context.h | 2 +- arch/x86/include/asm/shstk.h | 5 ++++- arch/x86/kernel/fpu/core.c | 36 ++++++++++++++++++++++++- arch/x86/kernel/process.c | 21 ++++++++++++++- arch/x86/kernel/shstk.c | 41 +++++++++++++++++++++++++++-- 6 files changed, 103 insertions(+), 5 deletions(-) diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h index c2d6cd7..3c2903b 100644 --- a/arch/x86/include/asm/fpu/sched.h +++ b/arch/x86/include/asm/fpu/sched.h @@ -11,7 +11,8 @@ extern void save_fpregs_to_fpstate(struct fpu *fpu); extern void fpu__drop(struct fpu *fpu); -extern int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal); +extern int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal, + unsigned long shstk_addr); extern void fpu_flush_thread(void); /* diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index e01aa74..9714f08 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -147,6 +147,8 @@ do { \ #else #define deactivate_mm(tsk, mm) \ do { \ + if (!tsk->vfork_done) \ + shstk_free(tsk); \ load_gs_index(0); \ loadsegment(fs, 0); \ } while (0) diff --git a/arch/x86/include/asm/shstk.h b/arch/x86/include/asm/shstk.h index 2b1f7c9..d4a5c7b 100644 --- a/arch/x86/include/asm/shstk.h +++ b/arch/x86/include/asm/shstk.h @@ -15,11 +15,16 @@ struct thread_shstk { long shstk_prctl(struct task_struct *task, int option, unsigned long features); void reset_thread_features(void); +unsigned long shstk_alloc_thread_stack(struct task_struct *p, unsigned long clone_flags, + unsigned long stack_size); void shstk_free(struct task_struct *p); #else static inline long shstk_prctl(struct task_struct *task, int option, unsigned long arg2) { return -EINVAL; } static inline void reset_thread_features(void) {} +static inline unsigned long shstk_alloc_thread_stack(struct task_struct *p, + unsigned long clone_flags, + unsigned long stack_size) { return 0; } static inline void shstk_free(struct task_struct *p) {} #endif /* CONFIG_X86_USER_SHADOW_STACK */ diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index f851558..aa4856b 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -552,8 +552,36 @@ static inline void fpu_inherit_perms(struct fpu *dst_fpu) } } +/* A passed ssp of zero will not cause any update */ +static int update_fpu_shstk(struct task_struct *dst, unsigned long ssp) +{ +#ifdef CONFIG_X86_USER_SHADOW_STACK + struct cet_user_state *xstate; + + /* If ssp update is not needed. */ + if (!ssp) + return 0; + + xstate = get_xsave_addr(&dst->thread.fpu.fpstate->regs.xsave, + XFEATURE_CET_USER); + + /* + * If there is a non-zero ssp, then 'dst' must be configured with a shadow + * stack and the fpu state should be up to date since it was just copied + * from the parent in fpu_clone(). So there must be a valid non-init CET + * state location in the buffer. + */ + if (WARN_ON_ONCE(!xstate)) + return 1; + + xstate->user_ssp = (u64)ssp; +#endif + return 0; +} + /* Clone current's FPU state on fork */ -int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal) +int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal, + unsigned long ssp) { struct fpu *src_fpu = ¤t->thread.fpu; struct fpu *dst_fpu = &dst->thread.fpu; @@ -613,6 +641,12 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal) if (use_xsave()) dst_fpu->fpstate->regs.xsave.header.xfeatures &= ~XFEATURE_MASK_PASID; + /* + * Update shadow stack pointer, in case it changed during clone. + */ + if (update_fpu_shstk(dst, ssp)) + return 1; + trace_x86_fpu_copy_src(src_fpu); trace_x86_fpu_copy_dst(dst_fpu); diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index b650cde..8bf13cf 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -48,6 +48,7 @@ #include #include #include +#include #include "process.h" @@ -119,6 +120,7 @@ void exit_thread(struct task_struct *tsk) free_vm86(t); + shstk_free(tsk); fpu__drop(fpu); } @@ -140,6 +142,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) struct inactive_task_frame *frame; struct fork_frame *fork_frame; struct pt_regs *childregs; + unsigned long new_ssp; int ret = 0; childregs = task_pt_regs(p); @@ -174,7 +177,16 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) frame->flags = X86_EFLAGS_FIXED; #endif - fpu_clone(p, clone_flags, args->fn); + /* + * Allocate a new shadow stack for thread if needed. If shadow stack, + * is disabled, new_ssp will remain 0, and fpu_clone() will know not to + * update it. + */ + new_ssp = shstk_alloc_thread_stack(p, clone_flags, args->stack_size); + if (IS_ERR_VALUE(new_ssp)) + return PTR_ERR((void *)new_ssp); + + fpu_clone(p, clone_flags, args->fn, new_ssp); /* Kernel thread ? */ if (unlikely(p->flags & PF_KTHREAD)) { @@ -220,6 +232,13 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP))) io_bitmap_share(p); + /* + * If copy_thread() if failing, don't leak the shadow stack possibly + * allocated in shstk_alloc_thread_stack() above. + */ + if (ret) + shstk_free(p); + return ret; } diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c index 3cb8522..bd9cdc3 100644 --- a/arch/x86/kernel/shstk.c +++ b/arch/x86/kernel/shstk.c @@ -47,7 +47,7 @@ static unsigned long alloc_shstk(unsigned long size) unsigned long addr, unused; mmap_write_lock(mm); - addr = do_mmap(NULL, addr, size, PROT_READ, flags, + addr = do_mmap(NULL, 0, size, PROT_READ, flags, VM_SHADOW_STACK | VM_WRITE, 0, &unused, NULL); mmap_write_unlock(mm); @@ -126,6 +126,37 @@ void reset_thread_features(void) current->thread.features_locked = 0; } +unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long clone_flags, + unsigned long stack_size) +{ + struct thread_shstk *shstk = &tsk->thread.shstk; + unsigned long addr, size; + + /* + * If shadow stack is not enabled on the new thread, skip any + * switch to a new shadow stack. + */ + if (!features_enabled(ARCH_SHSTK_SHSTK)) + return 0; + + /* + * For CLONE_VM, except vfork, the child needs a separate shadow + * stack. + */ + if ((clone_flags & (CLONE_VFORK | CLONE_VM)) != CLONE_VM) + return 0; + + size = adjust_shstk_size(stack_size); + addr = alloc_shstk(size); + if (IS_ERR_VALUE(addr)) + return addr; + + shstk->base = addr; + shstk->size = size; + + return addr + size; +} + void shstk_free(struct task_struct *tsk) { struct thread_shstk *shstk = &tsk->thread.shstk; @@ -134,7 +165,13 @@ void shstk_free(struct task_struct *tsk) !features_enabled(ARCH_SHSTK_SHSTK)) return; - if (!tsk->mm) + /* + * 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. + */ + if (!tsk->mm || tsk->mm != current->mm) return; unmap_shadow_stack(shstk->base, shstk->size);