From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7BABC433E0 for ; Tue, 19 Jan 2021 18:55:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9A37D20776 for ; Tue, 19 Jan 2021 18:55:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729338AbhASSzO (ORCPT ); Tue, 19 Jan 2021 13:55:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:48618 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390431AbhASS1e (ORCPT ); Tue, 19 Jan 2021 13:27:34 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id C86892388E; Tue, 19 Jan 2021 17:41:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611078062; bh=aR0zZuYtP0niTyCDTasWnxw5vYy4R+RIxCykasEXdGg=; h=From:To:Cc:Subject:Date:From; b=CqW2Cylk34362atGoLHnhyRFZ3dN4BLz0RriiwQcwLOc1wk54JSxHnHe1CmEfROA2 r9efOgEsxgHtqNtn70J7BeE8KVV9RNqrvlR1BTIfkLFjS6WLsLF/AWrgKc6OWD8RDd QdrD9oOJ00LVb5YvdooX5ssqHxaB3cYZElVtdQ+eMdbJkc3N8fV5gRzgUBgwxQjsmk XnWog363VCpRreLhlqxj4+odgMW5Rf7R5bLWwzlmzslgsk/8t1U1yXsqTKbRqZVqYW ZgJbAcw1fWdSrcA4LV5fFau9NAzPwNShWVpULCLL5QwmF7KyfWR4YsrakDYOK7/oHj TR3G/QpFTdujQ== From: Andy Lutomirski To: x86@kernel.org Cc: LKML , Andy Lutomirski , Andrea Arcangeli , Linux-MM , Jason Gunthorpe , Linus Torvalds , Matthew Wilcox , Jann Horn , Jan Kara , Yu Zhao , Peter Xu , Stas Sergeev , Brian Gerst Subject: [PATCH v2] x86/vm86/32: Remove VM86_SCREEN_BITMAP support Date: Tue, 19 Jan 2021 09:40:55 -0800 Message-Id: X-Mailer: git-send-email 2.29.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The implementation was rather buggy. It unconditionally marked PTEs read-only, even for VM_SHARED mappings. I'm not sure whether this is actually a problem, but it certainly seems unwise. More importantly, it released the mmap lock before flushing the TLB, which could allow a racing CoW operation to falsely believe that the underlying memory was not writable. I can't find any users at all of this mechanism, so just remove it. Cc: Andrea Arcangeli Cc: Linux-MM Cc: Jason Gunthorpe Cc: x86@kernel.org Cc: Linus Torvalds Cc: Matthew Wilcox Cc: Jann Horn Cc: Jan Kara Cc: Yu Zhao Cc: Peter Xu Cc: Stas Sergeev Cc: Brian Gerst Signed-off-by: Andy Lutomirski --- Changes from v1: - Get rid of the whole screen_bitmap and the fault code, too. arch/x86/include/asm/vm86.h | 1 - arch/x86/include/uapi/asm/vm86.h | 4 +-- arch/x86/kernel/vm86_32.c | 62 ++++++++------------------------ arch/x86/mm/fault.c | 30 ---------------- 4 files changed, 16 insertions(+), 81 deletions(-) diff --git a/arch/x86/include/asm/vm86.h b/arch/x86/include/asm/vm86.h index 26efbec94448..9e8ac5073ecb 100644 --- a/arch/x86/include/asm/vm86.h +++ b/arch/x86/include/asm/vm86.h @@ -36,7 +36,6 @@ struct vm86 { unsigned long saved_sp0; unsigned long flags; - unsigned long screen_bitmap; unsigned long cpu_type; struct revectored_struct int_revectored; struct revectored_struct int21_revectored; diff --git a/arch/x86/include/uapi/asm/vm86.h b/arch/x86/include/uapi/asm/vm86.h index d2ee4e307ef8..18909b8050bc 100644 --- a/arch/x86/include/uapi/asm/vm86.h +++ b/arch/x86/include/uapi/asm/vm86.h @@ -97,7 +97,7 @@ struct revectored_struct { struct vm86_struct { struct vm86_regs regs; unsigned long flags; - unsigned long screen_bitmap; + unsigned long screen_bitmap; /* unused, preserved by vm86() */ unsigned long cpu_type; struct revectored_struct int_revectored; struct revectored_struct int21_revectored; @@ -106,7 +106,7 @@ struct vm86_struct { /* * flags masks */ -#define VM86_SCREEN_BITMAP 0x0001 +#define VM86_SCREEN_BITMAP 0x0001 /* no longer supported */ struct vm86plus_info_struct { unsigned long force_return_for_pic:1; diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c index 764573de3996..e5a7a10a0164 100644 --- a/arch/x86/kernel/vm86_32.c +++ b/arch/x86/kernel/vm86_32.c @@ -134,7 +134,11 @@ void save_v86_state(struct kernel_vm86_regs *regs, int retval) unsafe_put_user(regs->ds, &user->regs.ds, Efault_end); unsafe_put_user(regs->fs, &user->regs.fs, Efault_end); unsafe_put_user(regs->gs, &user->regs.gs, Efault_end); - unsafe_put_user(vm86->screen_bitmap, &user->screen_bitmap, Efault_end); + + /* + * Don't write screen_bitmap in case some user had a value there + * and expected it to remain unchanged. + */ user_access_end(); @@ -160,49 +164,6 @@ void save_v86_state(struct kernel_vm86_regs *regs, int retval) do_exit(SIGSEGV); } -static void mark_screen_rdonly(struct mm_struct *mm) -{ - struct vm_area_struct *vma; - spinlock_t *ptl; - pgd_t *pgd; - p4d_t *p4d; - pud_t *pud; - pmd_t *pmd; - pte_t *pte; - int i; - - mmap_write_lock(mm); - pgd = pgd_offset(mm, 0xA0000); - if (pgd_none_or_clear_bad(pgd)) - goto out; - p4d = p4d_offset(pgd, 0xA0000); - if (p4d_none_or_clear_bad(p4d)) - goto out; - pud = pud_offset(p4d, 0xA0000); - if (pud_none_or_clear_bad(pud)) - goto out; - pmd = pmd_offset(pud, 0xA0000); - - if (pmd_trans_huge(*pmd)) { - vma = find_vma(mm, 0xA0000); - split_huge_pmd(vma, pmd, 0xA0000); - } - if (pmd_none_or_clear_bad(pmd)) - goto out; - pte = pte_offset_map_lock(mm, pmd, 0xA0000, &ptl); - for (i = 0; i < 32; i++) { - if (pte_present(*pte)) - set_pte(pte, pte_wrprotect(*pte)); - pte++; - } - pte_unmap_unlock(pte, ptl); -out: - mmap_write_unlock(mm); - flush_tlb_mm_range(mm, 0xA0000, 0xA0000 + 32*PAGE_SIZE, PAGE_SHIFT, false); -} - - - static int do_vm86_irq_handling(int subfunction, int irqnumber); static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus); @@ -282,6 +243,15 @@ static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus) offsetof(struct vm86_struct, int_revectored))) return -EFAULT; + + /* VM86_SCREEN_BITMAP had numerous bugs and appears to have no users. */ + if (v.flags & VM86_SCREEN_BITMAP) { + char comm[TASK_COMM_LEN]; + + pr_info_once("vm86: '%s' uses VM86_SCREEN_BITMAP, which is no longer supported\n", get_task_comm(comm, current)); + return -EINVAL; + } + memset(&vm86regs, 0, sizeof(vm86regs)); vm86regs.pt.bx = v.regs.ebx; @@ -302,7 +272,6 @@ static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus) vm86regs.gs = v.regs.gs; vm86->flags = v.flags; - vm86->screen_bitmap = v.screen_bitmap; vm86->cpu_type = v.cpu_type; if (copy_from_user(&vm86->int_revectored, @@ -370,9 +339,6 @@ static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus) update_task_stack(tsk); preempt_enable(); - if (vm86->flags & VM86_SCREEN_BITMAP) - mark_screen_rdonly(tsk->mm); - memcpy((struct kernel_vm86_regs *)regs, &vm86regs, sizeof(vm86regs)); return regs->ax; } diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 82bf37a5c9ec..fd0dd60f6302 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -261,25 +261,6 @@ void arch_sync_kernel_mappings(unsigned long start, unsigned long end) } } -/* - * Did it hit the DOS screen memory VA from vm86 mode? - */ -static inline void -check_v8086_mode(struct pt_regs *regs, unsigned long address, - struct task_struct *tsk) -{ -#ifdef CONFIG_VM86 - unsigned long bit; - - if (!v8086_mode(regs) || !tsk->thread.vm86) - return; - - bit = (address - 0xA0000) >> PAGE_SHIFT; - if (bit < 32) - tsk->thread.vm86->screen_bitmap |= 1 << bit; -#endif -} - static bool low_pfn(unsigned long pfn) { return pfn < max_low_pfn; @@ -334,15 +315,6 @@ KERN_ERR "******* Disabling USB legacy in the BIOS may also help.\n"; #endif -/* - * No vm86 mode in 64-bit mode: - */ -static inline void -check_v8086_mode(struct pt_regs *regs, unsigned long address, - struct task_struct *tsk) -{ -} - static int bad_address(void *p) { unsigned long dummy; @@ -1395,8 +1367,6 @@ void do_user_addr_fault(struct pt_regs *regs, mm_fault_error(regs, hw_error_code, address, fault); return; } - - check_v8086_mode(regs, address, tsk); } NOKPROBE_SYMBOL(do_user_addr_fault); -- 2.29.2