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 53874C4167B for ; Fri, 9 Dec 2022 10:51:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229564AbiLIKvg (ORCPT ); Fri, 9 Dec 2022 05:51:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59142 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229538AbiLIKvf (ORCPT ); Fri, 9 Dec 2022 05:51:35 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 4459D326D2 for ; Fri, 9 Dec 2022 02:51:34 -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 9D12E23A; Fri, 9 Dec 2022 02:51:40 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.39.232]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9D6E33F73B; Fri, 9 Dec 2022 02:51:32 -0800 (PST) Date: Fri, 9 Dec 2022 10:51:24 +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, Sami Tolvanen , Kees Cook Subject: Re: [PATCH 1/2] arm64: efi: Execute runtime services from a dedicated stack Message-ID: References: <20221205201210.463781-1-ardb@kernel.org> <20221205201210.463781-2-ardb@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221205201210.463781-2-ardb@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org Hi Ard, One drive-by comment below... On Mon, Dec 05, 2022 at 09:12:09PM +0100, Ard Biesheuvel wrote: > With the introduction of PRMT in the ACPI subsystem, the EFI rts > workqueue is no longer the only caller of efi_call_virt_pointer() in the > kernel. This means the EFI runtime services lock is no longer sufficient > to manage concurrent calls into firmware, but also that firmware calls > may occur that are not marshalled via the workqueue mechanism, but > originate directly from the caller context. > > For added robustness, and to ensure that the runtime services have 8 KiB > of stack space available as per the EFI spec, introduce a spinlock > protected EFI runtime stack of 8 KiB, where the spinlock also ensures > serialization between the EFI rts workqueue (which itself serializes EFI > runtime calls) and other callers of efi_call_virt_pointer(). > > While at it, use the stack pivot to avoid reloading the shadow call > stack pointer from the ordinary stack, as doing so could produce a > gadget to defeat it. > > Signed-off-by: Ard Biesheuvel > --- > arch/arm64/include/asm/efi.h | 3 +++ > arch/arm64/kernel/efi-rt-wrapper.S | 13 +++++++++- > arch/arm64/kernel/efi.c | 25 ++++++++++++++++++++ We'll need to teach the stack unwinder about this, or if we take an exception from the EFI stack, the backtrace will terminate as soon as it hits a frame record on the EFI stack. In arch/arm64/kernel/stacktrace.c's arch_stack_walk(), that'll need to be added to the array of stack bounds. Ideally we'd only add that when a thread is making an EFI call. Thanks, Mark. > 3 files changed, 40 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h > index 7c12e01c2b312e7b..1c408ec3c8b3a883 100644 > --- a/arch/arm64/include/asm/efi.h > +++ b/arch/arm64/include/asm/efi.h > @@ -25,6 +25,7 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md); > ({ \ > efi_virtmap_load(); \ > __efi_fpsimd_begin(); \ > + spin_lock(&efi_rt_lock); \ > }) > > #undef arch_efi_call_virt > @@ -33,10 +34,12 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md); > > #define arch_efi_call_virt_teardown() \ > ({ \ > + spin_unlock(&efi_rt_lock); \ > __efi_fpsimd_end(); \ > efi_virtmap_unload(); \ > }) > > +extern spinlock_t efi_rt_lock; > efi_status_t __efi_rt_asm_wrapper(void *, const char *, ...); > > #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 75691a2641c1c0f8..b2786b968fee68dd 100644 > --- a/arch/arm64/kernel/efi-rt-wrapper.S > +++ b/arch/arm64/kernel/efi-rt-wrapper.S > @@ -16,6 +16,12 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) > */ > stp x1, x18, [sp, #16] > > + ldr_l x16, efi_rt_stack_top > + mov sp, x16 > +#ifdef CONFIG_SHADOW_CALL_STACK > + str x18, [sp, #-16]! > +#endif > + > /* > * We are lucky enough that no EFI runtime services take more than > * 5 arguments, so all are passed in registers rather than via the > @@ -29,6 +35,7 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) > mov x4, x6 > blr x8 > > + mov sp, x29 > ldp x1, x2, [sp, #16] > cmp x2, x18 > ldp x29, x30, [sp], #32 > @@ -42,6 +49,10 @@ SYM_FUNC_START(__efi_rt_asm_wrapper) > * called with preemption disabled and a separate shadow stack is used > * for interrupts. > */ > - mov x18, x2 > +#ifdef CONFIG_SHADOW_CALL_STACK > + ldr_l x18, efi_rt_stack_top > + ldr x18, [x18, #-16] > +#endif > + > b efi_handle_corrupted_x18 // tail call > SYM_FUNC_END(__efi_rt_asm_wrapper) > diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c > index a908a37f03678b6b..8cb2e005f8aca589 100644 > --- a/arch/arm64/kernel/efi.c > +++ b/arch/arm64/kernel/efi.c > @@ -144,3 +144,28 @@ asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f) > pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f); > return s; > } > + > +DEFINE_SPINLOCK(efi_rt_lock); > + > +asmlinkage u64 *efi_rt_stack_top __ro_after_init; > + > +/* required by the EFI spec */ > +static_assert(THREAD_SIZE >= SZ_8K); > + > +int __init arm64_efi_rt_init(void) > +{ > + void *p = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN, > + VMALLOC_START, VMALLOC_END, GFP_KERNEL, > + PAGE_KERNEL, 0, NUMA_NO_NODE, > + __builtin_return_address(0)); > + > + if (!p) { > + pr_warn("Failed to allocate EFI runtime stack\n"); > + clear_bit(EFI_RUNTIME_SERVICES, &efi.flags); > + return -ENOMEM; > + } > + > + efi_rt_stack_top = p + THREAD_SIZE; > + return 0; > +} > +core_initcall(arm64_efi_rt_init); > -- > 2.35.1 >