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bh=FTkE8SfNE6dzRFrNyVwG9cvTvjVvHRxb1O0DRwg34/g=; b=ADpaxRcDUQUu59BQTRhPqoQPwc2FqyE3OWAVB2brv6qB2OlsovmE4DavH08hnDLJ7xGZWO lFgntYPXbrJ6/aDDEK61/gEbi02KC9fJqqSfUR/rfrnkwigCkTdgKFXMTupXzuYaVVV3nv FxTLyU7WIpzzdBkeQO/L1dOEtBve4Ak= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-461-HbpgYJm1ME20S55ECx5g6Q-1; Mon, 19 Dec 2022 11:30:23 -0500 X-MC-Unique: HbpgYJm1ME20S55ECx5g6Q-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C64453828882; Mon, 19 Dec 2022 16:30:22 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.194.120]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1A2AD40C945A; Mon, 19 Dec 2022 16:30:18 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, David Hildenbrand , Linus Torvalds , Andrew Morton , Arnd Bergmann , Greg Kroah-Hartman , Nicolas Pitre , Jens Axboe , Pavel Begunkov Subject: [PATCH mm-stable RFC 1/2] mm/nommu: factor out check for NOMMU shared mappings into is_nommu_shared_mapping() Date: Mon, 19 Dec 2022 17:30:12 +0100 Message-Id: <20221219163013.259423-2-david@redhat.com> In-Reply-To: <20221219163013.259423-1-david@redhat.com> References: <20221219163013.259423-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BF9961C0025 X-Stat-Signature: 4rfegchoihp17qhc3hyiwrk9f7pxfgfh X-HE-Tag: 1671467427-987792 X-HE-Meta: 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 vuoKM+XJ fNwp5ea3rbUIHsWGg3FTbsAFffFMQzyDRVYqn+SHijGKrRTntKdCseTGwqB6Q8r4m0Y/j 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: We want to stop using VM_MAYSHARE in private mappings to pave the way for clarifying the semantics of VM_MAYSHARE vs. VM_SHARED and reduce the confusion. While CONFIG_MMU uses VM_MAYSHARE to represent MAP_SHARED, !CONFIG_MMU also sets VM_MAYSHARE for selected R/O private file mappings that are an effective overlay of a file mapping. Let's factor out all relevant VM_MAYSHARE checks in !CONFIG_MMU code into is_nommu_shared_mapping() first. Note that whenever VM_SHARED is set, VM_MAYSHARE must be set as well (unless there is a serious BUG). So there is not need to test for VM_SHARED manually. No functional change intended. Signed-off-by: David Hildenbrand --- drivers/char/mem.c | 2 +- fs/cramfs/inode.c | 2 +- fs/proc/task_nommu.c | 2 +- fs/ramfs/file-nommu.c | 2 +- fs/romfs/mmap-nommu.c | 2 +- include/linux/mm.h | 15 +++++++++++++++ io_uring/io_uring.c | 2 +- mm/nommu.c | 11 ++++++----- 8 files changed, 27 insertions(+), 11 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 83bf2a4dcb57..ffb101d349f0 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -343,7 +343,7 @@ static unsigned zero_mmap_capabilities(struct file *file) /* can't do an in-place private mapping if there's no MMU */ static inline int private_mapping_ok(struct vm_area_struct *vma) { - return vma->vm_flags & VM_MAYSHARE; + return is_nommu_shared_mapping(vma->vm_flags); } #else diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c index 61ccf7722fc3..50e4e060db68 100644 --- a/fs/cramfs/inode.c +++ b/fs/cramfs/inode.c @@ -437,7 +437,7 @@ static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma) static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma) { - return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS; + return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -ENOSYS; } static unsigned long cramfs_physmem_get_unmapped_area(struct file *file, diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c index 2fd06f52b6a4..0ec35072a8e5 100644 --- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -38,7 +38,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm) } if (atomic_read(&mm->mm_count) > 1 || - vma->vm_flags & VM_MAYSHARE) { + is_nommu_shared_mapping(vma->vm_flags)) { sbytes += size; } else { bytes += size; diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c index cb240eac5036..cd4537692751 100644 --- a/fs/ramfs/file-nommu.c +++ b/fs/ramfs/file-nommu.c @@ -264,7 +264,7 @@ static unsigned long ramfs_nommu_get_unmapped_area(struct file *file, */ static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma) { - if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) + if (!is_nommu_shared_mapping(vma->vm_flags)) return -ENOSYS; file_accessed(file); diff --git a/fs/romfs/mmap-nommu.c b/fs/romfs/mmap-nommu.c index 2c4a23113fb5..4578dc45e50a 100644 --- a/fs/romfs/mmap-nommu.c +++ b/fs/romfs/mmap-nommu.c @@ -63,7 +63,7 @@ static unsigned long romfs_get_unmapped_area(struct file *file, */ static int romfs_mmap(struct file *file, struct vm_area_struct *vma) { - return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS; + return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -ENOSYS; } static unsigned romfs_mmap_capabilities(struct file *file) diff --git a/include/linux/mm.h b/include/linux/mm.h index f3f196e4d66d..734d0bc7c7c6 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1363,6 +1363,21 @@ static inline bool is_cow_mapping(vm_flags_t flags) return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; } +#ifndef CONFIG_MMU +static inline bool is_nommu_shared_mapping(vm_flags_t flags) +{ + /* + * NOMMU shared mappings are ordinary MAP_SHARED mappings and selected + * R/O MAP_PRIVATE file mappings that are an effective R/O overlay of + * a file mapping. R/O MAP_PRIVATE mappings might still modify + * underlying memory if ptrace is active, so this is only possible if + * ptrace does not apply. Note that there is no mprotect() to upgrade + * write permissions later. + */ + return flags & VM_MAYSHARE; +} +#endif + #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) #define SECTION_IN_PAGE_FLAGS #endif diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index b521186efa5c..84fa23b1f782 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -3174,7 +3174,7 @@ static __cold int io_uring_mmap(struct file *file, struct vm_area_struct *vma) static int io_uring_mmap(struct file *file, struct vm_area_struct *vma) { - return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -EINVAL; + return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -EINVAL; } static unsigned int io_uring_nommu_mmap_capabilities(struct file *file) diff --git a/mm/nommu.c b/mm/nommu.c index 214c70e1d059..6c4bdc07a776 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -958,9 +958,10 @@ static int do_mmap_private(struct vm_area_struct *vma, */ if (capabilities & NOMMU_MAP_DIRECT) { ret = call_mmap(vma->vm_file, vma); + /* shouldn't return success if we're not sharing */ + if (WARN_ON_ONCE(!is_nommu_shared_mapping(vma->vm_flags))) + ret = -ENOSYS; if (ret == 0) { - /* shouldn't return success if we're not sharing */ - BUG_ON(!(vma->vm_flags & VM_MAYSHARE)); vma->vm_region->vm_top = vma->vm_region->vm_end; return 0; } @@ -1106,7 +1107,7 @@ unsigned long do_mmap(struct file *file, * these cases, sharing is handled in the driver or filesystem rather * than here */ - if (vm_flags & VM_MAYSHARE) { + if (is_nommu_shared_mapping(vm_flags)) { struct vm_region *pregion; unsigned long pglen, rpglen, pgend, rpgend, start; @@ -1116,7 +1117,7 @@ unsigned long do_mmap(struct file *file, for (rb = rb_first(&nommu_region_tree); rb; rb = rb_next(rb)) { pregion = rb_entry(rb, struct vm_region, vm_rb); - if (!(pregion->vm_flags & VM_MAYSHARE)) + if (!is_nommu_shared_mapping(pregion->vm_flags)) continue; /* search for overlapping mappings on the same file */ @@ -1597,7 +1598,7 @@ static unsigned long do_mremap(unsigned long addr, if (vma->vm_end != vma->vm_start + old_len) return (unsigned long) -EFAULT; - if (vma->vm_flags & VM_MAYSHARE) + if (is_nommu_shared_mapping(vma->vm_flags)) return (unsigned long) -EPERM; if (new_len > vma->vm_region->vm_end - vma->vm_region->vm_start)