From: Kees Cook keescook@chromium.org
commit 314eed30ede02fa925990f535652254b5bad6b65 upstream.
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 rdunlap@infradead.org Tested-by: Randy Dunlap rdunlap@infradead.org Fixes: f5509cc18daa ("mm: Hardened usercopy") Cc: Matthew Wilcox willy@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Kees Cook keescook@chromium.org Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org Link: https://lore.kernel.org/r/201909171056.7F2FFD17@keescook Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/usercopy.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -15,6 +15,7 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/mm.h> +#include <linux/highmem.h> #include <linux/slab.h> #include <linux/sched.h> #include <linux/sched/task.h> @@ -203,7 +204,12 @@ static inline const char *check_heap_obj if (!virt_addr_valid(ptr)) return NULL;
- 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));
/* Check slab allocator for flags and size. */ if (PageSlab(page))