From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA411C433EF for ; Mon, 25 Apr 2022 11:56:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238554AbiDYL7m (ORCPT ); Mon, 25 Apr 2022 07:59:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35116 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236443AbiDYL7Z (ORCPT ); Mon, 25 Apr 2022 07:59:25 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 31303B1CC for ; Mon, 25 Apr 2022 04:56:19 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EAA8D1FB; Mon, 25 Apr 2022 04:56:18 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 92BDF3F73B; Mon, 25 Apr 2022 04:56:17 -0700 (PDT) From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, alex.popov@linux.com, catalin.marinas@arm.com, keescook@chromium.org, linux-arm-kernel@lists.infradead.org, luto@kernel.org, mark.rutland@arm.com, will@kernel.org Subject: [PATCH 4/8] stackleak: clarify variable names Date: Mon, 25 Apr 2022 12:55:59 +0100 Message-Id: <20220425115603.781311-5-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220425115603.781311-1-mark.rutland@arm.com> References: <20220425115603.781311-1-mark.rutland@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The logic within __stackleak_erase() can be a little hard to follow, as `boundary` switches from being the low bound to the high bound mid way through the function, and `kstack_ptr` is used to represent the start of the region to erase while `boundary` represents the end of the region to erase. Make this a little clearer by consistently using clearer variable names. The `boundary` variable is removed, the bounds of the region to erase are described by `erase_low` and `erase_high`, and bounds of the task stack are described by `task_stack_low` and `task_stck_high`. As the same time, remove the comment above the variables, since it is unclear whether it's intended as rationale, a complaint, or a TODO, and is more confusing than helpful. There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland Cc: Alexander Popov Cc: Andrew Morton Cc: Andy Lutomirski Cc: Kees Cook --- kernel/stackleak.c | 34 ++++++++++++++++------------------ 1 file changed, 16 insertions(+), 18 deletions(-) diff --git a/kernel/stackleak.c b/kernel/stackleak.c index 0472956d9a2ce..8fbc1e4c21435 100644 --- a/kernel/stackleak.c +++ b/kernel/stackleak.c @@ -73,44 +73,42 @@ late_initcall(stackleak_sysctls_init); static __always_inline void __stackleak_erase(void) { const unsigned long task_stack_low = stackleak_task_low_bound(current); - - /* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */ - unsigned long kstack_ptr = current->lowest_stack; - unsigned long boundary = task_stack_low; + unsigned long erase_low = current->lowest_stack; + unsigned long erase_high; unsigned int poison_count = 0; const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long); /* Check that 'lowest_stack' value is sane */ - if (unlikely(kstack_ptr - boundary >= THREAD_SIZE)) - kstack_ptr = boundary; + if (unlikely(erase_low - task_stack_low >= THREAD_SIZE)) + erase_low = task_stack_low; /* Search for the poison value in the kernel stack */ - while (kstack_ptr > boundary && poison_count <= depth) { - if (*(unsigned long *)kstack_ptr == STACKLEAK_POISON) + while (erase_low > task_stack_low && poison_count <= depth) { + if (*(unsigned long *)erase_low == STACKLEAK_POISON) poison_count++; else poison_count = 0; - kstack_ptr -= sizeof(unsigned long); + erase_low -= sizeof(unsigned long); } #ifdef CONFIG_STACKLEAK_METRICS - current->prev_lowest_stack = kstack_ptr; + current->prev_lowest_stack = erase_low; #endif /* - * Now write the poison value to the kernel stack. Start from - * 'kstack_ptr' and move up till the new 'boundary'. We assume that - * the stack pointer doesn't change when we write poison. + * Now write the poison value to the kernel stack between 'erase_low' + * and 'erase_high'. We assume that the stack pointer doesn't change + * when we write poison. */ if (on_thread_stack()) - boundary = current_stack_pointer; + erase_high = current_stack_pointer; else - boundary = current_top_of_stack(); + erase_high = current_top_of_stack(); - while (kstack_ptr < boundary) { - *(unsigned long *)kstack_ptr = STACKLEAK_POISON; - kstack_ptr += sizeof(unsigned long); + while (erase_low < erase_high) { + *(unsigned long *)erase_low = STACKLEAK_POISON; + erase_low += sizeof(unsigned long); } /* Reset the 'lowest_stack' value for the next syscall */ -- 2.30.2