The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 80d82ca9562bb881f2884ccb33b5530d40144450 Gitweb: https://git.kernel.org/tip/80d82ca9562bb881f2884ccb33b5530d40144450 Author: Kees Cook keescook@chromium.org AuthorDate: Mon, 19 Sep 2022 13:16:48 -07:00 Committer: Dave Hansen dave.hansen@linux.intel.com CommitterDate: Tue, 20 Sep 2022 14:43:49 -07:00

x86/uaccess: Avoid check_object_size() in copy_from_user_nmi()

The check_object_size() helper under CONFIG_HARDENED_USERCOPY is designed to skip any checks where the length is known at compile time as a reasonable heuristic to avoid "likely known-good" cases. However, it can only do this when the copy_*_user() helpers are, themselves, inline too.

Using find_vmap_area() requires taking a spinlock. The check_object_size() helper can call find_vmap_area() when the destination is in vmap memory. If show_regs() is called in interrupt context, it will attempt a call to copy_from_user_nmi(), which may call check_object_size() and then find_vmap_area(). If something in normal context happens to be in the middle of calling find_vmap_area() (with the spinlock held), the interrupt handler will hang forever.

The copy_from_user_nmi() call is actually being called with a fixed-size length, so check_object_size() should never have been called in the first place. Given the narrow constraints, just replace the __copy_from_user_inatomic() call with an open-coded version that calls only into the sanitizers and not check_object_size(), followed by a call to raw_copy_from_user().

Fixes: 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns") Reported-by: Yu Zhao yuzhao@google.com Reported-by: dev@der-flo.net Suggested-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Tested-by: Florian Lehner dev@der-flo.net Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b... Link: https://lkml.kernel.org/r/20220919201648.2250764-1-keescook@chromium.org --- arch/x86/lib/usercopy.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c index ad0139d..d2aff9b 100644 --- a/arch/x86/lib/usercopy.c +++ b/arch/x86/lib/usercopy.c @@ -44,7 +44,8 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n) * called from other contexts. */ pagefault_disable(); - ret = __copy_from_user_inatomic(to, from, n); + instrument_copy_from_user(to, from, n); + ret = raw_copy_from_user(to, from, n); pagefault_enable();

return ret;