From 314eed30ede02fa925990f535652254b5bad6b65 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 17 Sep 2019 11:00:25 -0700 Subject: [PATCH] usercopy: Avoid HIGHMEM pfn warning When running on a system with >512MB RAM with a 32-bit kernel built with: CONFIG_DEBUG_VIRTUAL=y CONFIG_HIGHMEM=y CONFIG_HARDENED_USERCOPY=y all execve()s will fail due to argv copying into kmap()ed pages, and on usercopy checking the calls ultimately of virt_to_page() will be looking for "bad" kmap (highmem) pointers due to CONFIG_DEBUG_VIRTUAL=y: ------------[ cut here ]------------ kernel BUG at ../arch/x86/mm/physaddr.c:83! invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.3.0-rc8 #6 Hardware name: Dell Inc. Inspiron 1318/0C236D, BIOS A04 01/15/2009 EIP: __phys_addr+0xaf/0x100 ... Call Trace: __check_object_size+0xaf/0x3c0 ? __might_sleep+0x80/0xa0 copy_strings+0x1c2/0x370 copy_strings_kernel+0x2b/0x40 __do_execve_file+0x4ca/0x810 ? kmem_cache_alloc+0x1c7/0x370 do_execve+0x1b/0x20 ... The check is from arch/x86/mm/physaddr.c: VIRTUAL_BUG_ON((phys_addr >> PAGE_SHIFT) > max_low_pfn); Due to the kmap() in fs/exec.c: kaddr = kmap(kmapped_page); ... if (copy_from_user(kaddr+offset, str, bytes_to_copy)) ... Now we can fetch the correct page to avoid the pfn check. In both cases, hardened usercopy will need to walk the page-span checker (if enabled) to do sanity checking. Reported-by: Randy Dunlap Tested-by: Randy Dunlap Fixes: f5509cc18daa ("mm: Hardened usercopy") Cc: Matthew Wilcox Cc: stable@vger.kernel.org Signed-off-by: Kees Cook Reviewed-by: Matthew Wilcox (Oracle) Link: https://lore.kernel.org/r/201909171056.7F2FFD17@keescook --- mm/usercopy.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/usercopy.c b/mm/usercopy.c index 98e924864554..660717a1ea5c 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -11,6 +11,7 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include +#include #include #include #include @@ -227,7 +228,12 @@ static inline void check_heap_object(const void *ptr, unsigned long n, if (!virt_addr_valid(ptr)) return; - page = virt_to_head_page(ptr); + /* + * When CONFIG_HIGHMEM=y, kmap_to_page() will give either the + * highmem page or fallback to virt_to_page(). The following + * is effectively a highmem-aware virt_to_head_page(). + */ + page = compound_head(kmap_to_page((void *)ptr)); if (PageSlab(page)) { /* Check slab allocator for flags and size. */