From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga03.intel.com ([134.134.136.65]:18256 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751207AbdBWW3I (ORCPT ); Thu, 23 Feb 2017 17:29:08 -0500 Subject: [PATCH 1/2] x86, pkeys: check against max pkey to avoid overflows To: linux-kernel@vger.kernel.org Cc: x86@kernel.org, Dave Hansen , kirill.shutemov@linux.intel.com, shuah@kernel.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org From: Dave Hansen Date: Thu, 23 Feb 2017 14:26:03 -0800 Message-Id: <20170223222603.A022ED65@viggo.jf.intel.com> Sender: stable-owner@vger.kernel.org List-ID: From: Dave Hansen Kirill got a warning from UBSAN about undefined behavior when using protection keys. He is running on hardware that actually has support for it, which is not widely available. The warning was because we did some very large shifts of integers when doing a pkey_free() of a large, invalid value because we never check that the pkey "fits" into the mm_pkey_allocation_map(). I do not believe there is any danger here of anything bad happening other than some aliasing issues where somebody could do: pkey_free(35); and the kernel would effectively execute: pkey_free(8); While this might be confusing to an app that was doing something stupid, it has to do something stupid and the effects are limited to the app shooting itself in the foot. Signed-off-by: Dave Hansen Cc: Kirill A. Shutemov Cc: Shuah Khan Cc: linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: x86@kernel.org Cc: stable@vger.kernel.org --- b/arch/x86/include/asm/pkeys.h | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff -puN arch/x86/include/asm/pkeys.h~do-max-pkey-check arch/x86/include/asm/pkeys.h --- a/arch/x86/include/asm/pkeys.h~do-max-pkey-check 2017-02-23 14:17:33.291953218 -0800 +++ b/arch/x86/include/asm/pkeys.h 2017-02-23 14:24:32.573666333 -0800 @@ -46,6 +46,15 @@ extern int __arch_set_user_pkey_access(s static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) { + /* + * "Allocated" pkeys are those that have been returned + * from pkey_alloc(). pkey 0 is special, and never + * returned from pkey_alloc(). + */ + if (pkey <= 0) + return false; + if (pkey >= arch_max_pkey()) + return false; return mm_pkey_allocation_map(mm) & (1U << pkey); } @@ -82,12 +91,6 @@ int mm_pkey_alloc(struct mm_struct *mm) static inline int mm_pkey_free(struct mm_struct *mm, int pkey) { - /* - * pkey 0 is special, always allocated and can never - * be freed. - */ - if (!pkey) - return -EINVAL; if (!mm_pkey_is_allocated(mm, pkey)) return -EINVAL; _