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 41EF5C67871 for ; Mon, 9 Jan 2023 13:26:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233330AbjAIN0x (ORCPT ); Mon, 9 Jan 2023 08:26:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42370 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230005AbjAIN0x (ORCPT ); Mon, 9 Jan 2023 08:26:53 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 52AFC8FE2 for ; Mon, 9 Jan 2023 05:26:51 -0800 (PST) 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 E3D7DC14; Mon, 9 Jan 2023 05:27:32 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.46.123]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D5C833F23F; Mon, 9 Jan 2023 05:26:49 -0800 (PST) Date: Mon, 9 Jan 2023 13:26:43 +0000 From: Mark Rutland To: Ard Biesheuvel Cc: linux-efi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, will@kernel.org, catalin.marinas@arm.com, Lee Jones Subject: Re: [PATCH v3 1/2] arm64: efi: Avoid workqueue to check whether EFI runtime is live Message-ID: References: <20230106174703.1883495-1-ardb@kernel.org> <20230106174703.1883495-2-ardb@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230106174703.1883495-2-ardb@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org On Fri, Jan 06, 2023 at 06:47:02PM +0100, Ard Biesheuvel wrote: > Comparing current_work() against efi_rts_work.work is sufficient to > decide whether current is currently running EFI runtime services code at > any level in its call stack. > > However, there are other potential users of the EFI runtime stack, such > as the ACPI subsystem, which may invoke efi_call_virt_pointer() > directly, and so any sync exceptions occurring in firmware during those > calls are currently misidentified. > > So instead, let's check whether 'current' has preemption disabled, and > whether the stashed value of the thread stack pointer points into > current's thread stack. This can only be the case if current was > interrupted while running EFI runtime code. This implies that we should > clear the stashed value after switching back, to avoid false positives. > > Signed-off-by: Ard Biesheuvel Reviewed-by: Mark Rutland Thanks for this! Mark. > --- > arch/arm64/include/asm/efi.h | 9 +++++++++ > arch/arm64/kernel/efi-rt-wrapper.S | 6 ++++++ > arch/arm64/kernel/efi.c | 3 ++- > 3 files changed, 17 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h > index 31d13a6001df49c4..f68d13c3a44e7bb2 100644 > --- a/arch/arm64/include/asm/efi.h > +++ b/arch/arm64/include/asm/efi.h > @@ -48,8 +48,17 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md); > }) > > extern spinlock_t efi_rt_lock; > +extern u64 *efi_rt_stack_top; > efi_status_t __efi_rt_asm_wrapper(void *, const char *, ...); > > +/* > + * efi_rt_stack_top[-1] contains the value the stack pointer had before > + * switching to the EFI runtime stack. > + */ > +#define current_in_efi() \ > + (!preemptible() && \ > + on_task_stack(current, READ_ONCE(efi_rt_stack_top[-1]), 1)) > + > #define ARCH_EFI_IRQ_FLAGS_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT) > > /* > diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S > index a00886410537d6a6..11f3ec9f09e86de6 100644 > --- a/arch/arm64/kernel/efi-rt-wrapper.S > +++ b/arch/arm64/kernel/efi-rt-wrapper.S > @@ -45,7 +45,10 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) > mov x4, x6 > blr x8 > > + mov x16, sp > mov sp, x29 > + str xzr, [x16, #8] // clear recorded task SP value > + > ldp x1, x2, [sp, #16] > cmp x2, x18 > ldp x29, x30, [sp], #112 > @@ -70,6 +73,9 @@ SYM_FUNC_END(__efi_rt_asm_wrapper) > SYM_CODE_START(__efi_rt_asm_recover) > mov sp, x30 > > + ldr_l x16, efi_rt_stack_top // clear recorded task SP value > + str xzr, [x16, #-8] > + > ldp x19, x20, [sp, #32] > ldp x21, x22, [sp, #48] > ldp x23, x24, [sp, #64] > diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c > index fab05de2e12dd5d8..b273900f45668587 100644 > --- a/arch/arm64/kernel/efi.c > +++ b/arch/arm64/kernel/efi.c > @@ -11,6 +11,7 @@ > #include > > #include > +#include > > static bool region_is_misaligned(const efi_memory_desc_t *md) > { > @@ -154,7 +155,7 @@ asmlinkage efi_status_t __efi_rt_asm_recover(void); > bool efi_runtime_fixup_exception(struct pt_regs *regs, const char *msg) > { > /* Check whether the exception occurred while running the firmware */ > - if (current_work() != &efi_rts_work.work || regs->pc >= TASK_SIZE_64) > + if (!current_in_efi() || regs->pc >= TASK_SIZE_64) > return false; > > pr_err(FW_BUG "Unable to handle %s in EFI runtime service\n", msg); > -- > 2.39.0 >