From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlastimil Babka Subject: [PATCH v2 1/2] mm/mincore: make mincore() more conservative Date: Tue, 12 Mar 2019 15:17:07 +0100 Message-ID: <20190312141708.6652-2-vbabka@suse.cz> References: <20190130124420.1834-1-vbabka@suse.cz> <20190312141708.6652-1-vbabka@suse.cz> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190312141708.6652-1-vbabka@suse.cz> Sender: linux-kernel-owner@vger.kernel.org To: Andrew Morton Cc: Linus Torvalds , Jann Horn , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Jiri Kosina , Dominique Martinet , Andy Lutomirski , Dave Chinner , Kevin Easton , Matthew Wilcox , Cyril Hrubis , Tejun Heo , "Kirill A . Shutemov" , Daniel Gruss , Vlastimil Babka , Josh Snyder , Michal Hocko , Jiri Kosina List-Id: linux-api@vger.kernel.org From: Jiri Kosina The semantics of what mincore() considers to be resident is not completely clear, but Linux has always (since 2.3.52, which is when mincore() was initially done) treated it as "page is available in page cache". That's potentially a problem, as that [in]directly exposes meta-information about pagecache / memory mapping state even about memory not strictly belonging to the process executing the syscall, opening possibilities for sidechannel attacks. Change the semantics of mincore() so that it only reveals pagecache information for non-anonymous mappings that belog to files that the calling process could (if it tried to) successfully open for writing; otherwise we'd be including shared non-exclusive mappings, which - is the sidechannel - is not the usecase for mincore(), as that's primarily used for data, not (shared) text [mhocko@suse.com: restructure can_do_mincore() conditions] Originally-by: Linus Torvalds Originally-by: Dominique Martinet Cc: Dominique Martinet Cc: Andy Lutomirski Cc: Dave Chinner Cc: Kevin Easton Cc: Matthew Wilcox Cc: Cyril Hrubis Cc: Tejun Heo Cc: Kirill A. Shutemov Cc: Daniel Gruss Signed-off-by: Jiri Kosina Signed-off-by: Vlastimil Babka Acked-by: Josh Snyder Acked-by: Michal Hocko Signed-off-by: Jiri Kosina Signed-off-by: Vlastimil Babka --- mm/mincore.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/mm/mincore.c b/mm/mincore.c index 218099b5ed31..c3f058bd0faf 100644 --- a/mm/mincore.c +++ b/mm/mincore.c @@ -169,6 +169,22 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, return 0; } +static inline bool can_do_mincore(struct vm_area_struct *vma) +{ + if (vma_is_anonymous(vma)) + return true; + if (!vma->vm_file) + return false; + /* + * Reveal pagecache information only for non-anonymous mappings that + * correspond to the files the calling process could (if tried) open + * for writing; otherwise we'd be including shared non-exclusive + * mappings, which opens a side channel. + */ + return inode_owner_or_capable(file_inode(vma->vm_file)) || + inode_permission(file_inode(vma->vm_file), MAY_WRITE) == 0; +} + /* * Do a chunk of "sys_mincore()". We've already checked * all the arguments, we hold the mmap semaphore: we should @@ -189,8 +205,13 @@ static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *v vma = find_vma(current->mm, addr); if (!vma || addr < vma->vm_start) return -ENOMEM; - mincore_walk.mm = vma->vm_mm; end = min(vma->vm_end, addr + (pages << PAGE_SHIFT)); + if (!can_do_mincore(vma)) { + unsigned long pages = DIV_ROUND_UP(end - addr, PAGE_SIZE); + memset(vec, 1, pages); + return pages; + } + mincore_walk.mm = vma->vm_mm; err = walk_page_range(addr, end, &mincore_walk); if (err < 0) return err; -- 2.20.1