From patchwork Fri Oct 27 10:51:09 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dave Martin X-Patchwork-Id: 10029595 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 4EC1F602D6 for ; Fri, 27 Oct 2017 10:56:31 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3CDC328F4C for ; Fri, 27 Oct 2017 10:56:31 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 2EDD628F52; Fri, 27 Oct 2017 10:56:31 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [65.50.211.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 76E1C28F4C for ; Fri, 27 Oct 2017 10:56:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:MIME-Version:Cc:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:References: In-Reply-To:Message-Id:Date:Subject:To:From:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=8SlkU8QChLvNvb/fKZdKNMdlaPA5X4DhXPffN0KrFLU=; b=jQoAMjWxuUcsijOD1tBb6tUBR8 aHik6jZ1KdkRKNf+Zr6gTHZXvXmQtknUJ546VQlkp/NMT10vILKGFMOWG48egWV6Q58hm6ZyVyJmI 3rhM6Bz+M+e0P0/cUqPNyT8RiFWfKP7ISNNPBK5U6Oo4FKrd/Ii7DP8J7mSw932uG4eliAfKzdDlZ jVyfcy3OgxPpgyboat/m+xgosn5QjsC7FwnDnUpYxUabuUuqz5F8x5KmHgiXYjyQYDn0K0KyIbz7R y4dvz7DeY1OtIvZM+SJIA9S6olebLFG/4/e/ZBxGCi17bEdMqyIdTV1tUKrNYY+QUYOvdbEJZUuFZ bq52GgwA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1e82JR-0008LY-Gf; Fri, 27 Oct 2017 10:56:29 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1e82FN-0003vr-Qj for linux-arm-kernel@lists.infradead.org; Fri, 27 Oct 2017 10:52:39 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C587D1A9A; Fri, 27 Oct 2017 03:52:12 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 166843F24A; Fri, 27 Oct 2017 03:52:10 -0700 (PDT) From: Dave Martin To: linux-arm-kernel@lists.infradead.org Subject: [RFC PATCH v4 27/28] arm64: signal: Report signal frame size to userspace via auxv Date: Fri, 27 Oct 2017 11:51:09 +0100 Message-Id: <1509101470-7881-28-git-send-email-Dave.Martin@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1509101470-7881-1-git-send-email-Dave.Martin@arm.com> References: <1509101470-7881-1-git-send-email-Dave.Martin@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20171027_035218_270256_833C2B6D X-CRM114-Status: GOOD ( 17.90 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Okamoto Takayuki , libc-alpha@sourceware.org, Ard Biesheuvel , Szabolcs Nagy , Catalin Marinas , Will Deacon , =?UTF-8?q?Alex=20Benn=C3=A9e?= , kvmarm@lists.cs.columbia.edu MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Stateful CPU architecture extensions may require the signal frame to grow to a size that exceeds the arch's MINSIGSTKSZ #define. However, changing this #define is an ABI break. To allow userspace the option of determining the signal frame size in a more forwards-compatible way, this patch adds a new auxv entry tagged with AT_MINSIGSTKSZ, which provides the maximum signal frame size that the process can observe during its lifetime. If AT_MINSIGSTKSZ is absent from the aux vector, the caller can assume that the MINSIGSTKSZ #define is sufficient. This allows for a consistent interface with older kernels that do not provide AT_MINSIGSTKSZ. The idea is that libc could expose this via sysconf() or some similar mechanism. There is deliberately no AT_SIGSTKSZ. The kernel knows nothing about userspace's own stack overheads and should not pretend to know. For arm64: The primary motivation for this interface is the Scalable Vector Extension, which can require at least 4KB or so of extra space in the signal frame for the largest hardware implementations. To determine the correct value, a "Christmas tree" mode (via the add_all argument) is added to setup_sigframe_layout(), to simulate addition of all possible records to the signal frame at maximum possible size. If this procedure goes wrong somehow, resulting in a stupidly large frame layout and hence failure of sigframe_alloc() to allocate a record to the frame, then this is indicative of a kernel bug: the kernel's internal SIGFRAME_MAXSZ is supposed to sanity-check against generting frames that we consider _impossibly_ large. In this case, SIGSTKSZ is returned as a "reasonable guess that is at least bigger than MINSIGSTKSZ" and we WARN(). Signed-off-by: Dave Martin --- arch/arm64/include/asm/elf.h | 5 +++++ arch/arm64/include/asm/processor.h | 3 +++ arch/arm64/include/uapi/asm/auxvec.h | 3 ++- arch/arm64/kernel/signal.c | 39 +++++++++++++++++++++++++++++++----- 4 files changed, 44 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h index fac1c4d..771c7a8 100644 --- a/arch/arm64/include/asm/elf.h +++ b/arch/arm64/include/asm/elf.h @@ -24,6 +24,10 @@ #include #include +#ifndef __ASSEMBLY__ +#include /* for get_minsigstksz(), used by ARCH_DLINFO */ +#endif + /* * AArch64 static relocation types. */ @@ -148,6 +152,7 @@ typedef struct user_fpsimd_state elf_fpregset_t; do { \ NEW_AUX_ENT(AT_SYSINFO_EHDR, \ (elf_addr_t)current->mm->context.vdso); \ + NEW_AUX_ENT(AT_MINSIGSTKSZ, get_minsigstksz()); \ } while (0) #define ARCH_HAS_SETUP_ADDITIONAL_PAGES diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 023cacb..055b06d 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -217,6 +217,9 @@ static inline void spin_lock_prefetch(const void *ptr) int cpu_enable_pan(void *__unused); int cpu_enable_cache_maint_trap(void *__unused); +/* User signal frame size discovery: */ +int get_minsigstksz(void); + /* Userspace interface for PR_SVE_{SET,GET}_VL prctl()s: */ #define SVE_SET_VL(arg) sve_set_current_vl(arg) #define SVE_GET_VL() sve_get_current_vl() diff --git a/arch/arm64/include/uapi/asm/auxvec.h b/arch/arm64/include/uapi/asm/auxvec.h index 4cf0c17..1d45b28 100644 --- a/arch/arm64/include/uapi/asm/auxvec.h +++ b/arch/arm64/include/uapi/asm/auxvec.h @@ -18,7 +18,8 @@ /* vDSO location */ #define AT_SYSINFO_EHDR 33 +#define AT_MINSIGSTKSZ 34 /* stack needed for signal delivery */ -#define AT_VECTOR_SIZE_ARCH 1 /* entries in ARCH_DLINFO */ +#define AT_VECTOR_SIZE_ARCH 2 /* entries in ARCH_DLINFO */ #endif diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 79bc55a..ecae147 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -567,8 +567,15 @@ asmlinkage long sys_rt_sigreturn(struct pt_regs *regs) return 0; } -/* Determine the layout of optional records in the signal frame */ -static int setup_sigframe_layout(struct rt_sigframe_user_layout *user) +/* + * Determine the layout of optional records in the signal frame + * + * add_all: if true, lays out the biggest possible signal frame for + * this task; otherwise, generates a layout for the current state + * of the task. + */ +static int setup_sigframe_layout(struct rt_sigframe_user_layout *user, + bool add_all) { int err; @@ -578,7 +585,7 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user) return err; /* fault information, if valid */ - if (current->thread.fault_code) { + if (add_all || current->thread.fault_code) { err = sigframe_alloc(user, &user->esr_offset, sizeof(struct esr_context)); if (err) @@ -600,7 +607,6 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user) return sigframe_alloc_end(user); } - static int setup_sigframe(struct rt_sigframe_user_layout *user, struct pt_regs *regs, sigset_t *set) { @@ -698,7 +704,7 @@ static int get_sigframe(struct rt_sigframe_user_layout *user, int err; init_user_layout(user); - err = setup_sigframe_layout(user); + err = setup_sigframe_layout(user, false); if (err) return err; @@ -930,3 +936,26 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, thread_flags = READ_ONCE(current_thread_info()->flags); } while (thread_flags & _TIF_WORK_MASK); } + +/* + * Determine the stack space required for guaranteed signal devliery. + * This function is used to populate AT_MINSIGSTKSZ at process startup. + */ +int get_minsigstksz(void) +{ + struct rt_sigframe_user_layout user; + int err; + + init_user_layout(&user); + err = setup_sigframe_layout(&user, true); + + if (err) { + WARN_ON(1); + + return SIGSTKSZ; + } else { + return sigframe_size(&user) + + round_up(sizeof(struct frame_record), 16) + + 16; /* max alignment padding */ + } +}