| Message ID | 20211213142703.3066590-4-willy@infradead.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Assorted improvements to usercopy | expand |
On Mon, Dec 13, 2021 at 02:27:03PM +0000, Matthew Wilcox (Oracle) wrote: > Move the compound page overrun detection out of > CONFIG_HARDENED_USERCOPY_PAGESPAN so it's enabled for more people. I'd argue that everything else enabled by USERCOPY_PAGESPAN could be removed now too. Do you want to add a 4th patch to rip that out? https://github.com/KSPP/linux/issues/163 Thanks! -Kees
On Mon, Dec 13, 2021 at 12:52:22PM -0800, Kees Cook wrote: > On Mon, Dec 13, 2021 at 02:27:03PM +0000, Matthew Wilcox (Oracle) wrote: > > Move the compound page overrun detection out of > > CONFIG_HARDENED_USERCOPY_PAGESPAN so it's enabled for more people. > > I'd argue that everything else enabled by USERCOPY_PAGESPAN could be > removed now too. Do you want to add a 4th patch to rip that out? > > https://github.com/KSPP/linux/issues/163 I don't mind ... is it your assessment that it's not worth checking for a copy_to/from_user that spans a boundary between a reserved and !reserved page, or overlaps the boundary of rodata/bss/data/CMA? I have no basis on which to judge that, so it's really up to you.
On Mon, Dec 13, 2021 at 11:44:33PM +0000, Matthew Wilcox wrote: > On Mon, Dec 13, 2021 at 12:52:22PM -0800, Kees Cook wrote: > > On Mon, Dec 13, 2021 at 02:27:03PM +0000, Matthew Wilcox (Oracle) wrote: > > > Move the compound page overrun detection out of > > > CONFIG_HARDENED_USERCOPY_PAGESPAN so it's enabled for more people. > > > > I'd argue that everything else enabled by USERCOPY_PAGESPAN could be > > removed now too. Do you want to add a 4th patch to rip that out? > > > > https://github.com/KSPP/linux/issues/163 > > I don't mind ... is it your assessment that it's not worth checking for > a copy_to/from_user that spans a boundary between a reserved and > !reserved page, or overlaps the boundary of rodata/bss/data/CMA? > > I have no basis on which to judge that, so it's really up to you. It's always been a problem because some arch mark the kernel as reserved, so we have to do all the allow-listing first, which is tedious. I'd certainly like to add all the checks possible, but rationally, we need to keep only the stuff that is fast, useful, or both. PAGESPAN has been disabled almost everywhere, too, so I don't think it's a loss.
diff --git a/mm/usercopy.c b/mm/usercopy.c index 63476e1506e0..db2e8c4f79fd 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -163,7 +163,6 @@ static inline void check_page_span(const void *ptr, unsigned long n, { #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN const void *end = ptr + n - 1; - struct page *endpage; bool is_reserved, is_cma; /* @@ -194,11 +193,6 @@ static inline void check_page_span(const void *ptr, unsigned long n, ((unsigned long)end & (unsigned long)PAGE_MASK))) return; - /* Allow if fully inside the same compound (__GFP_COMP) page. */ - endpage = virt_to_head_page(end); - if (likely(endpage == page)) - return; - /* * Reject if range is entirely either Reserved (i.e. special or * device memory), or CMA. Otherwise, reject since the object spans @@ -258,6 +252,11 @@ static inline void check_heap_object(const void *ptr, unsigned long n, if (PageSlab(page)) { /* Check slab allocator for flags and size. */ __check_heap_object(ptr, n, page, to_user); + } else if (PageHead(page)) { + /* A compound allocation */ + unsigned long offset = ptr - page_address(page); + if (offset + n > page_size(page)) + usercopy_abort("page alloc", NULL, to_user, offset, n); } else { /* Verify object does not incorrectly span multiple pages. */ check_page_span(ptr, n, page, to_user);