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From: Jann Horn <jannh@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Oleg Nesterov <oleg@redhat.com>
Subject: [PATCH v4 1/5] binfmt_elf_fdpic: Stop using dump_emit() on user pointers on !MMU
Date: Wed, 26 Aug 2020 17:14:44 +0200	[thread overview]
Message-ID: <20200826151448.3404695-2-jannh@google.com> (raw)
In-Reply-To: <20200826151448.3404695-1-jannh@google.com>

dump_emit() is for kernel pointers, and VMAs describe userspace memory.
Let's be tidy here and avoid accessing userspace pointers under KERNEL_DS,
even if it probably doesn't matter much on !MMU systems - especially given
that it looks like we can just use the same get_dump_page() as on MMU if
we move it out of the CONFIG_MMU block.

One small change we have to make in get_dump_page() is to use
__get_user_pages_locked() instead of __get_user_pages(), since the
latter doesn't exist on nommu. On mmu builds, __get_user_pages_locked()
will just call __get_user_pages() for us.

Signed-off-by: Jann Horn <jannh@google.com>
---
 fs/binfmt_elf_fdpic.c |  8 ------
 mm/gup.c              | 57 +++++++++++++++++++++----------------------
 2 files changed, 28 insertions(+), 37 deletions(-)

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 50f845702b92..a53f83830986 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1529,14 +1529,11 @@ static bool elf_fdpic_dump_segments(struct coredump_params *cprm)
 	struct vm_area_struct *vma;
 
 	for (vma = current->mm->mmap; vma; vma = vma->vm_next) {
-#ifdef CONFIG_MMU
 		unsigned long addr;
-#endif
 
 		if (!maydump(vma, cprm->mm_flags))
 			continue;
 
-#ifdef CONFIG_MMU
 		for (addr = vma->vm_start; addr < vma->vm_end;
 							addr += PAGE_SIZE) {
 			bool res;
@@ -1552,11 +1549,6 @@ static bool elf_fdpic_dump_segments(struct coredump_params *cprm)
 			if (!res)
 				return false;
 		}
-#else
-		if (!dump_emit(cprm, (void *) vma->vm_start,
-				vma->vm_end - vma->vm_start))
-			return false;
-#endif
 	}
 	return true;
 }
diff --git a/mm/gup.c b/mm/gup.c
index ae096ea7583f..92519e5a44b3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1495,35 +1495,6 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
 		mmap_read_unlock(mm);
 	return ret;	/* 0 or negative error code */
 }
-
-/**
- * get_dump_page() - pin user page in memory while writing it to core dump
- * @addr: user address
- *
- * Returns struct page pointer of user page pinned for dump,
- * to be freed afterwards by put_page().
- *
- * Returns NULL on any kind of failure - a hole must then be inserted into
- * the corefile, to preserve alignment with its headers; and also returns
- * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
- * allowing a hole to be left in the corefile to save diskspace.
- *
- * Called without mmap_lock, but after all other threads have been killed.
- */
-#ifdef CONFIG_ELF_CORE
-struct page *get_dump_page(unsigned long addr)
-{
-	struct vm_area_struct *vma;
-	struct page *page;
-
-	if (__get_user_pages(current->mm, addr, 1,
-			     FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
-			     NULL) < 1)
-		return NULL;
-	flush_cache_page(vma, addr, page_to_pfn(page));
-	return page;
-}
-#endif /* CONFIG_ELF_CORE */
 #else /* CONFIG_MMU */
 static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
 		unsigned long nr_pages, struct page **pages,
@@ -1569,6 +1540,34 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
 }
 #endif /* !CONFIG_MMU */
 
+/**
+ * get_dump_page() - pin user page in memory while writing it to core dump
+ * @addr: user address
+ *
+ * Returns struct page pointer of user page pinned for dump,
+ * to be freed afterwards by put_page().
+ *
+ * Returns NULL on any kind of failure - a hole must then be inserted into
+ * the corefile, to preserve alignment with its headers; and also returns
+ * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
+ * allowing a hole to be left in the corefile to save diskspace.
+ *
+ * Called without mmap_lock, but after all other threads have been killed.
+ */
+#ifdef CONFIG_ELF_CORE
+struct page *get_dump_page(unsigned long addr)
+{
+	struct vm_area_struct *vma;
+	struct page *page;
+
+	if (__get_user_pages_locked(current->mm, addr, 1, &page, &vma, NULL,
+				    FOLL_FORCE | FOLL_DUMP | FOLL_GET) < 1)
+		return NULL;
+	flush_cache_page(vma, addr, page_to_pfn(page));
+	return page;
+}
+#endif /* CONFIG_ELF_CORE */
+
 #if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
 static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
 {
-- 
2.28.0.297.g1956fa8f8d-goog


  reply	other threads:[~2020-08-26 15:17 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-26 15:14 [PATCH v4 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there Jann Horn
2020-08-26 15:14 ` Jann Horn [this message]
2020-08-26 15:14 ` [PATCH v4 2/5] coredump: Let dump_emit() bail out on short writes Jann Horn
2020-08-26 15:14 ` [PATCH v4 3/5] coredump: Refactor page range dumping into common helper Jann Horn
2020-08-26 15:14 ` [PATCH v4 4/5] binfmt_elf, binfmt_elf_fdpic: Use a VMA list snapshot Jann Horn
2020-08-26 17:14   ` Linus Torvalds
2020-08-26 15:14 ` [PATCH v4 5/5] mm/gup: Take mmap_lock in get_dump_page() Jann Horn
2020-08-26 17:15 ` [PATCH v4 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there Linus Torvalds

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