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 254B4C433EF for ; Wed, 30 Mar 2022 12:17:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347255AbiC3MTJ (ORCPT ); Wed, 30 Mar 2022 08:19:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344274AbiC3Lzp (ORCPT ); Wed, 30 Mar 2022 07:55:45 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DB24C2DA8F; Wed, 30 Mar 2022 04:53:50 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id C5C93615E7; Wed, 30 Mar 2022 11:53:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6A750C340EE; Wed, 30 Mar 2022 11:53:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648641229; bh=/7CWCV4WT0FmWQL0kHsiP32i0wPlYtof1bpijFqJ/ek=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fai1CDlfl1lCeeQVUTlWH+b2FjYF5rZDpD/20MHgLHT9oq62wmR+wPl0XjBvDHdoo aBiV40xy5zQgiLBbYd9s6G9Duw8f2zE66lxnf+lrQ9TZxwR4ProAwJOjoFkx3Jh8F7 cWaHIaH3sPETmwbBds0iSfrCz5n0NGoK6O+FVA38qoOMwVhpN329XEBcw+70dYY3yb KQ6pYUlUQTCvO8kS6xd9foVV/ffwL9GZS/0vcvmNmi9GKpuLbUNeYRAKkJUdNdyyhj nxCaooU9ZwfqtUhOjafBJWVzygnuS4VH2pG3tyr2Pqyio9Yd3AmNSiCOxpefgRfIcA 5H2GbmWZTKCaQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Ard Biesheuvel , Steven Rostedt , Sasha Levin , linux@armlinux.org.uk, linux-arm-kernel@lists.infradead.org Subject: [PATCH AUTOSEL 4.14 07/20] ARM: ftrace: avoid redundant loads or clobbering IP Date: Wed, 30 Mar 2022 07:53:23 -0400 Message-Id: <20220330115336.1672930-7-sashal@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220330115336.1672930-1-sashal@kernel.org> References: <20220330115336.1672930-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ard Biesheuvel [ Upstream commit d11967870815b5ab89843980e35aab616c97c463 ] Tweak the ftrace return paths to avoid redundant loads of SP, as well as unnecessary clobbering of IP. This also fixes the inconsistency of using MOV to perform a function return, which is sub-optimal on recent micro-architectures but more importantly, does not perform an interworking return, unlike compiler generated function returns in Thumb2 builds. Let's fix this by popping PC from the stack like most ordinary code does. Signed-off-by: Ard Biesheuvel Reviewed-by: Steven Rostedt (Google) Signed-off-by: Sasha Levin --- arch/arm/kernel/entry-ftrace.S | 51 +++++++++++++++------------------- 1 file changed, 22 insertions(+), 29 deletions(-) diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S index efcd9f25a14b..baae9ed1fb5b 100644 --- a/arch/arm/kernel/entry-ftrace.S +++ b/arch/arm/kernel/entry-ftrace.S @@ -41,10 +41,7 @@ * mcount can be thought of as a function called in the middle of a subroutine * call. As such, it needs to be transparent for both the caller and the * callee: the original lr needs to be restored when leaving mcount, and no - * registers should be clobbered. (In the __gnu_mcount_nc implementation, we - * clobber the ip register. This is OK because the ARM calling convention - * allows it to be clobbered in subroutines and doesn't use it to hold - * parameters.) + * registers should be clobbered. * * When using dynamic ftrace, we patch out the mcount call by a "mov r0, r0" * for the mcount case, and a "pop {lr}" for the __gnu_mcount_nc case (see @@ -96,26 +93,25 @@ .macro __ftrace_regs_caller - sub sp, sp, #8 @ space for PC and CPSR OLD_R0, + str lr, [sp, #-8]! @ store LR as PC and make space for CPSR/OLD_R0, @ OLD_R0 will overwrite previous LR - add ip, sp, #12 @ move in IP the value of SP as it was - @ before the push {lr} of the mcount mechanism + ldr lr, [sp, #8] @ get previous LR - str lr, [sp, #0] @ store LR instead of PC + str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR - ldr lr, [sp, #8] @ get previous LR + str lr, [sp, #-4]! @ store previous LR as LR - str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR + add lr, sp, #16 @ move in LR the value of SP as it was + @ before the push {lr} of the mcount mechanism - stmdb sp!, {ip, lr} - stmdb sp!, {r0-r11, lr} + push {r0-r11, ip, lr} @ stack content at this point: @ 0 4 48 52 56 60 64 68 72 - @ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 | + @ R0 | R1 | ... | IP | SP + 4 | previous LR | LR | PSR | OLD_R0 | - mov r3, sp @ struct pt_regs* + mov r3, sp @ struct pt_regs* ldr r2, =function_trace_op ldr r2, [r2] @ pointer to the current @@ -138,11 +134,9 @@ ftrace_graph_regs_call: #endif @ pop saved regs - ldmia sp!, {r0-r12} @ restore r0 through r12 - ldr ip, [sp, #8] @ restore PC - ldr lr, [sp, #4] @ restore LR - ldr sp, [sp, #0] @ restore SP - mov pc, ip @ return + pop {r0-r11, ip, lr} @ restore r0 through r12 + ldr lr, [sp], #4 @ restore LR + ldr pc, [sp], #12 .endm #ifdef CONFIG_FUNCTION_GRAPH_TRACER @@ -158,11 +152,9 @@ ftrace_graph_regs_call: bl prepare_ftrace_return @ pop registers saved in ftrace_regs_caller - ldmia sp!, {r0-r12} @ restore r0 through r12 - ldr ip, [sp, #8] @ restore PC - ldr lr, [sp, #4] @ restore LR - ldr sp, [sp, #0] @ restore SP - mov pc, ip @ return + pop {r0-r11, ip, lr} @ restore r0 through r12 + ldr lr, [sp], #4 @ restore LR + ldr pc, [sp], #12 .endm #endif @@ -273,16 +265,17 @@ ENDPROC(ftrace_graph_caller_old) .endm .macro mcount_exit - ldmia sp!, {r0-r3, ip, lr} - ret ip + ldmia sp!, {r0-r3} + ldr lr, [sp, #4] + ldr pc, [sp], #8 .endm ENTRY(__gnu_mcount_nc) UNWIND(.fnstart) #ifdef CONFIG_DYNAMIC_FTRACE - mov ip, lr - ldmia sp!, {lr} - ret ip + push {lr} + ldr lr, [sp, #4] + ldr pc, [sp], #8 #else __mcount #endif -- 2.34.1