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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 32B7BC3ABB5 for ; Wed, 30 Apr 2025 16:08:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Lfgl2PRBGDTmnLNnXIsMguAGQIHF6zw81qS+Lc6/FX0=; b=J4DA2E8Eo5RPltLeAZ0oDisLuV 0WvLVCrg9tM8sJ/deWESnQFcSHZ4aiLLKDIw9VZrFtbcVbveSP2O/K5+Oj0WN5rJ1UvjtmDG4wu99 fs0svL5ljQm6oR2dPaubIdD+dlyh9Qw338TEMBO8bi8nzOkriBvQSUljHPYZtDd53gHc8OPWrbu6r 1zDyZcpOqoZ0bkpA6IfclB+RCn4yjA1twfchCOObvoYSbLjRLr8SsiHRNQUIYSvH4E+o6PccigwYD w9PMte1oQ8tSECw8Zs3sp6kPKJ+lR7FvGNGOaM48SogvPtNBfTv1yNaPYF9Q8S+arVlVAyUMxT9bo FgqRJtvA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uA9zV-0000000DO2O-3JYy; Wed, 30 Apr 2025 16:08:57 +0000 Received: from s3.sipsolutions.net ([2a01:4f8:242:246e::2] helo=sipsolutions.net) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uA9wu-0000000DNgG-2r8c for linux-um@lists.infradead.org; Wed, 30 Apr 2025 16:06:18 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sipsolutions.net; s=mail; h=Content-Transfer-Encoding:MIME-Version: References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Content-Type:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-To: Resent-Cc:Resent-Message-ID; bh=Lfgl2PRBGDTmnLNnXIsMguAGQIHF6zw81qS+Lc6/FX0=; t=1746029176; x=1747238776; b=r+Y40cx8B9YQ5lRHH5yN67MefOG8dFHmFAMex0QlMaw1Vq7 Tdvmqz0bxed3nUbMbdN7JOoriS+hAZVkjMJQtwQl9JvhHF3le+TQ12LEbMxG52sBIjiR30ntASLiK Rav+NtRkWg6DtSlxAPs3HIsrP/+V6/3L8DQUNCIc9GOErwiHxn7fgjs0anp2tXXZt1lAf3gFAgpHF dltV+MArMAlZVec6OH0sneAvMc0OCuBs53+erubAdOJzdSsIqKw9MhDM4LMs4U/yNf7EJNv53MlzF 9mEmflcEy1aB/G1K5cZj9Aai+4aBzvD5td1IJ0EG4404yR4QsH/XeCCv6dPHzvJw==; Received: by sipsolutions.net with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.98.1) (envelope-from ) id 1uA9wr-0000000DxyX-1GA5; Wed, 30 Apr 2025 18:06:13 +0200 From: Benjamin Berg To: linux-um@lists.infradead.org Cc: Benjamin Berg , Benjamin Berg Subject: [PATCH v2 5/8] um: Track userspace children dying in SECCOMP mode Date: Wed, 30 Apr 2025 18:04:10 +0200 Message-ID: <20250430160413.3250227-6-benjamin@sipsolutions.net> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250430160413.3250227-1-benjamin@sipsolutions.net> References: <20250430160413.3250227-1-benjamin@sipsolutions.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250430_090616_899223_4CD7E77D X-CRM114-Status: GOOD ( 31.05 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org When in seccomp mode, we would hang forever on the futex if a child has died unexpectedly. In contrast, ptrace mode will notice it and kill the corresponding thread when it fails to run it. Fix this issue using a new IRQ that is fired after a SIGCHLD and keeping an (internal) list of all MMs. In the IRQ handler, find the affected MM and set its PID to -1 as well as the futex variable to FUTEX_IN_KERN. This, together with futex returning -EINTR after the signal is sufficient to implement a race-free detection of a child dying. Note that this also enables IRQ handling while starting a userspace process. This should be safe and SECCOMP requires the IRQ in case the process does not come up properly. Signed-off-by: Benjamin Berg Signed-off-by: Benjamin Berg --- v2: - Fix whitespace issue v1: - Permit IRQs during startup to enable detection there RFCv2: - Use "struct list_head" for the list by placing it into the mm_context --- arch/um/include/asm/irq.h | 5 +- arch/um/include/asm/mmu.h | 3 ++ arch/um/include/shared/irq_user.h | 2 + arch/um/include/shared/os.h | 1 + arch/um/include/shared/skas/mm_id.h | 2 + arch/um/kernel/irq.c | 6 +++ arch/um/kernel/skas/mmu.c | 82 +++++++++++++++++++++++++++-- arch/um/os-Linux/process.c | 31 +++++++++++ arch/um/os-Linux/signal.c | 19 ++++++- 9 files changed, 143 insertions(+), 8 deletions(-) diff --git a/arch/um/include/asm/irq.h b/arch/um/include/asm/irq.h index 749dfe8512e8..36dbedd1af48 100644 --- a/arch/um/include/asm/irq.h +++ b/arch/um/include/asm/irq.h @@ -13,17 +13,18 @@ #define TELNETD_IRQ 8 #define XTERM_IRQ 9 #define RANDOM_IRQ 10 +#define SIGCHLD_IRQ 11 #ifdef CONFIG_UML_NET_VECTOR -#define VECTOR_BASE_IRQ (RANDOM_IRQ + 1) +#define VECTOR_BASE_IRQ (SIGCHLD_IRQ + 1) #define VECTOR_IRQ_SPACE 8 #define UM_FIRST_DYN_IRQ (VECTOR_IRQ_SPACE + VECTOR_BASE_IRQ) #else -#define UM_FIRST_DYN_IRQ (RANDOM_IRQ + 1) +#define UM_FIRST_DYN_IRQ (SIGCHLD_IRQ + 1) #endif diff --git a/arch/um/include/asm/mmu.h b/arch/um/include/asm/mmu.h index a3eaca41ff61..4d0e4239f3cc 100644 --- a/arch/um/include/asm/mmu.h +++ b/arch/um/include/asm/mmu.h @@ -6,11 +6,14 @@ #ifndef __ARCH_UM_MMU_H #define __ARCH_UM_MMU_H +#include "linux/types.h" #include typedef struct mm_context { struct mm_id id; + struct list_head list; + /* Address range in need of a TLB sync */ unsigned long sync_tlb_range_from; unsigned long sync_tlb_range_to; diff --git a/arch/um/include/shared/irq_user.h b/arch/um/include/shared/irq_user.h index 88835b52ae2b..746abc24a5d5 100644 --- a/arch/um/include/shared/irq_user.h +++ b/arch/um/include/shared/irq_user.h @@ -17,6 +17,8 @@ enum um_irq_type { struct siginfo; extern void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs, void *mc); +extern void sigchld_handler(int sig, struct siginfo *unused_si, + struct uml_pt_regs *regs, void *mc); void sigio_run_timetravel_handlers(void); extern void free_irq_by_fd(int fd); extern void deactivate_fd(int fd, int irqnum); diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h index 152a60080d5b..39a6828bf78a 100644 --- a/arch/um/include/shared/os.h +++ b/arch/um/include/shared/os.h @@ -198,6 +198,7 @@ extern int create_mem_file(unsigned long long len); extern void report_enomem(void); /* process.c */ +pid_t os_reap_child(void); extern void os_alarm_process(int pid); extern void os_kill_process(int pid, int reap_child); extern void os_kill_ptraced_process(int pid, int reap_child); diff --git a/arch/um/include/shared/skas/mm_id.h b/arch/um/include/shared/skas/mm_id.h index 140388c282f6..0654c57bb28e 100644 --- a/arch/um/include/shared/skas/mm_id.h +++ b/arch/um/include/shared/skas/mm_id.h @@ -14,4 +14,6 @@ struct mm_id { void __switch_mm(struct mm_id *mm_idp); +void notify_mm_kill(int pid); + #endif diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c index abe8f30a521c..f1787be3983c 100644 --- a/arch/um/kernel/irq.c +++ b/arch/um/kernel/irq.c @@ -690,3 +690,9 @@ void __init init_IRQ(void) /* Initialize EPOLL Loop */ os_setup_epoll(); } + +extern void sigchld_handler(int sig, struct siginfo *unused_si, + struct uml_pt_regs *regs, void *mc) +{ + do_IRQ(SIGCHLD_IRQ, regs); +} diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c index 0eb5a1d3ba70..1e146a0f9549 100644 --- a/arch/um/kernel/skas/mmu.c +++ b/arch/um/kernel/skas/mmu.c @@ -8,6 +8,7 @@ #include #include +#include #include #include #include @@ -19,6 +20,9 @@ /* Ensure the stub_data struct covers the allocated area */ static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE); +spinlock_t mm_list_lock; +struct list_head mm_list; + int init_new_context(struct task_struct *task, struct mm_struct *mm) { struct mm_id *new_id = &mm->context.id; @@ -31,10 +35,12 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm) new_id->stack = stack; - block_signals_trace(); - new_id->pid = start_userspace(stack); - unblock_signals_trace(); + scoped_guard(spinlock_irqsave, &mm_list_lock) { + /* Insert into list, used for lookups when the child dies */ + list_add(&mm->context.list, &mm_list); + } + new_id->pid = start_userspace(stack); if (new_id->pid < 0) { ret = new_id->pid; goto out_free; @@ -60,13 +66,79 @@ void destroy_context(struct mm_struct *mm) * zero, resulting in a kill(0), which will result in the * whole UML suddenly dying. Also, cover negative and * 1 cases, since they shouldn't happen either. + * + * Negative cases happen if the child died unexpectedly. */ - if (mmu->id.pid < 2) { + if (mmu->id.pid >= 0 && mmu->id.pid < 2) { printk(KERN_ERR "corrupt mm_context - pid = %d\n", mmu->id.pid); return; } - os_kill_ptraced_process(mmu->id.pid, 1); + + if (mmu->id.pid > 0) { + os_kill_ptraced_process(mmu->id.pid, 1); + mmu->id.pid = -1; + } free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES)); + + guard(spinlock_irqsave)(&mm_list_lock); + + list_del(&mm->context.list); +} + +static irqreturn_t mm_sigchld_irq(int irq, void* dev) +{ + struct mm_context *mm_context; + pid_t pid; + + guard(spinlock)(&mm_list_lock); + + while ((pid = os_reap_child()) > 0) { + /* + * A child died, check if we have an MM with the PID. This is + * only relevant in SECCOMP mode (as ptrace will fail anyway). + * + * See wait_stub_done_seccomp for more details. + */ + list_for_each_entry(mm_context, &mm_list, list) { + if (mm_context->id.pid == pid) { + struct stub_data *stub_data; + printk("Unexpectedly lost MM child! Affected tasks will segfault."); + + /* Marks the MM as dead */ + mm_context->id.pid = -1; + + /* + * NOTE: If SMP is implemented, a futex_wake + * needs to be added here. + */ + stub_data = (void *)mm_context->id.stack; + stub_data->futex = FUTEX_IN_KERN; + + /* + * NOTE: Currently executing syscalls by + * affected tasks may finish normally. + */ + break; + } + } + } + + return IRQ_HANDLED; +} + +static int __init init_child_tracking(void) +{ + int err; + + spin_lock_init(&mm_list_lock); + INIT_LIST_HEAD(&mm_list); + + err = request_irq(SIGCHLD_IRQ, mm_sigchld_irq, 0, "SIGCHLD", NULL); + if (err < 0) + panic("Failed to register SIGCHLD IRQ: %d", err); + + return 0; } +early_initcall(init_child_tracking) diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c index 184566edeee9..00b49e90d05f 100644 --- a/arch/um/os-Linux/process.c +++ b/arch/um/os-Linux/process.c @@ -18,17 +18,29 @@ #include #include #include +#include void os_alarm_process(int pid) { + if (pid <= 0) + return; + kill(pid, SIGALRM); } void os_kill_process(int pid, int reap_child) { + if (pid <= 0) + return; + + /* Block signals until child is reaped */ + block_signals(); + kill(pid, SIGKILL); if (reap_child) CATCH_EINTR(waitpid(pid, NULL, __WALL)); + + unblock_signals(); } /* Kill off a ptraced child by all means available. kill it normally first, @@ -38,11 +50,27 @@ void os_kill_process(int pid, int reap_child) void os_kill_ptraced_process(int pid, int reap_child) { + if (pid <= 0) + return; + + /* Block signals until child is reaped */ + block_signals(); + kill(pid, SIGKILL); ptrace(PTRACE_KILL, pid); ptrace(PTRACE_CONT, pid); if (reap_child) CATCH_EINTR(waitpid(pid, NULL, __WALL)); + + unblock_signals(); +} + +pid_t os_reap_child(void) +{ + int status; + + /* Try to reap a child */ + return waitpid(-1, &status, WNOHANG); } /* Don't use the glibc version, which caches the result in TLS. It misses some @@ -151,6 +179,9 @@ void init_new_thread_signals(void) set_handler(SIGBUS); signal(SIGHUP, SIG_IGN); set_handler(SIGIO); + /* We (currently) only use the child reaper IRQ in seccomp mode */ + if (using_seccomp) + set_handler(SIGCHLD); signal(SIGWINCH, SIG_IGN); } diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c index e71e5b4878d1..11f07f498270 100644 --- a/arch/um/os-Linux/signal.c +++ b/arch/um/os-Linux/signal.c @@ -29,6 +29,7 @@ void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *, void *mc) = [SIGBUS] = relay_signal, [SIGSEGV] = segv_handler, [SIGIO] = sigio_handler, + [SIGCHLD] = sigchld_handler, }; static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc) @@ -44,7 +45,7 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc) } /* enable signals if sig isn't IRQ signal */ - if ((sig != SIGIO) && (sig != SIGWINCH)) + if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGCHLD)) unblock_signals_trace(); (*sig_info[sig])(sig, si, &r, mc); @@ -64,6 +65,9 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc) #define SIGALRM_BIT 1 #define SIGALRM_MASK (1 << SIGALRM_BIT) +#define SIGCHLD_BIT 2 +#define SIGCHLD_MASK (1 << SIGCHLD_BIT) + int signals_enabled; #if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT) static int signals_blocked, signals_blocked_pending; @@ -102,6 +106,11 @@ static void sig_handler(int sig, struct siginfo *si, mcontext_t *mc) return; } + if (!enabled && (sig == SIGCHLD)) { + signals_pending |= SIGCHLD_MASK; + return; + } + block_signals_trace(); sig_handler_common(sig, si, mc); @@ -181,6 +190,8 @@ static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = { [SIGIO] = sig_handler, [SIGWINCH] = sig_handler, + /* SIGCHLD is only actually registered in seccomp mode. */ + [SIGCHLD] = sig_handler, [SIGALRM] = timer_alarm_handler, [SIGUSR1] = sigusr1_handler, @@ -309,6 +320,12 @@ void unblock_signals(void) if (save_pending & SIGIO_MASK) sig_handler_common(SIGIO, NULL, NULL); + if (save_pending & SIGCHLD_MASK) { + struct uml_pt_regs regs = {}; + + sigchld_handler(SIGCHLD, NULL, ®s, NULL); + } + /* Do not reenter the handler */ if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK))) -- 2.49.0