From 59298997df89e19aad426d4ae0a7e5037074da5a Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 19 Sep 2022 13:16:48 -0700 Subject: [PATCH] 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(). [akpm@linux-foundation.org: no instrument_copy_from_user() in my tree...] Link: https://lkml.kernel.org/r/20220919201648.2250764-1-keescook@chromium.org Link: https://lore.kernel.org/all/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b3EQ@mail.gmail.com Fixes: 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns") Signed-off-by: Kees Cook Reported-by: Yu Zhao Reported-by: Florian Lehner Suggested-by: Andrew Morton Acked-by: Peter Zijlstra (Intel) Tested-by: Florian Lehner Cc: Matthew Wilcox Cc: Josh Poimboeuf Cc: Dave Hansen Cc: Signed-off-by: Andrew Morton --- arch/x86/lib/usercopy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c index ad0139d25401..f1bb18617156 100644 --- a/arch/x86/lib/usercopy.c +++ b/arch/x86/lib/usercopy.c @@ -44,7 +44,7 @@ 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); + ret = raw_copy_from_user(to, from, n); pagefault_enable(); return ret;