From: Jiri Kosina jkosina@suse.cz
commit 134fca9063ad4851de767d1768180e5dede9a881 upstream.
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
[jkosina@suse.cz: v2] Link: http://lkml.kernel.org/r/20190312141708.6652-2-vbabka@suse.cz [mhocko@suse.com: restructure can_do_mincore() conditions] Link: http://lkml.kernel.org/r/nycvar.YFH.7.76.1903062342020.19912@cbobk.fhfr.pm Signed-off-by: Jiri Kosina jkosina@suse.cz Signed-off-by: Vlastimil Babka vbabka@suse.cz Acked-by: Josh Snyder joshs@netflix.com Acked-by: Michal Hocko mhocko@suse.com Originally-by: Linus Torvalds torvalds@linux-foundation.org Originally-by: Dominique Martinet asmadeus@codewreck.org Cc: Andy Lutomirski luto@amacapital.net Cc: Dave Chinner david@fromorbit.com Cc: Kevin Easton kevin@guarana.org Cc: Matthew Wilcox willy@infradead.org Cc: Cyril Hrubis chrubis@suse.cz Cc: Tejun Heo tj@kernel.org Cc: Kirill A. Shutemov kirill@shutemov.name Cc: Daniel Gruss daniel@gruss.cc Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/mincore.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-)
--- a/mm/mincore.c +++ b/mm/mincore.c @@ -165,6 +165,22 @@ out: 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 @@ -185,8 +201,13 @@ static long do_mincore(unsigned long add 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;