From nobody Sat Feb 7 21:05:38 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 63BAC1F3BA4 for ; Sun, 11 Jan 2026 15:00:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768143656; cv=none; b=Wbyau9J7i6XpJYUjC2lFY14if4cZoDpcuqtRDkz3o/z+O+AieOUddrhqMv7kV7OsiL2WSkIiu11HSOd7HScfFnATEMmpP3LsUWMtUgxBx2HfH74ljk3ld3B/Rm1RoCKRhuBZI5VEb94FsmqoZ5LrCgDsL/yoIDp4E4pjzpCVGL4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768143656; c=relaxed/simple; bh=J92KQBBOQqp5YYhfpONQU/yld6bmdPsMMQDpwfM9DeM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HIi2w5pYgS+pwjMTZyISto1vpJqRrfO+iyg5703oUjH18SwnqjzWHXMOh5lMPwuIQWgsnPFTIO5V8PYCi4sGuFvazNy2pSQMk4S5/9as/PiBGgeGTD+uY9kBr0tiOFs5EecIsdwZVRl5gO4ra5nPuM9EACV4jZ21kpA2WxMu1Mo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=eZ+1oR1F; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="eZ+1oR1F" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1768143653; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=4pLNx05At1IckXxdFbGhri2hHg2/BXAlfQXxSA/Jmjk=; b=eZ+1oR1FpSJTkFHCZg2QOnb7u1znlTTGF6QklBUeUB5WQASH48d1c30S2+Z5KUyJ98n2aT a4gKb2XTOhfo+bMFeVZwaou/uEHOcShvd44myW8JucNrS/hYPrSLJK7kcS1eR9UPlqvJ0w 4Zp8GlYASOzZQgjBb/Kh3so/BHv3xYo= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-684-Yk04FhfGPpGXc7qzrCoXfg-1; Sun, 11 Jan 2026 10:00:47 -0500 X-MC-Unique: Yk04FhfGPpGXc7qzrCoXfg-1 X-Mimecast-MFC-AGG-ID: Yk04FhfGPpGXc7qzrCoXfg_1768143645 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 00EA41956089; Sun, 11 Jan 2026 15:00:44 +0000 (UTC) Received: from fedora (unknown [10.44.33.200]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id D9A02180009E; Sun, 11 Jan 2026 15:00:38 +0000 (UTC) Received: by fedora (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sun, 11 Jan 2026 16:00:43 +0100 (CET) Date: Sun, 11 Jan 2026 16:00:37 +0100 From: Oleg Nesterov To: Andrii Nakryiko , Borislav Petkov , Dave Hansen , David Hildenbrand , "H. Peter Anvin" , Ingo Molnar , Jiri Olsa , Masami Hiramatsu , Paulo Andrade , Peter Zijlstra , Thomas Gleixner Cc: linux-kernel@vger.kernel.org, x86@kernel.org Subject: [PATCH] x86/uprobes: Fix XOL allocation failure for 32-bit tasks Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This script #!/usr/bin/bash echo 0 > /proc/sys/kernel/randomize_va_space echo 'void main(void) {}' > TEST.c # -fcf-protection to ensure that the 1st endbr32 insn can't be emulated gcc -m32 -fcf-protection=3Dbranch TEST.c -o test bpftrace -e 'uprobe:./test:main {}' -c ./test "hangs", the probed ./test task enters an endless loop. The problem is that with randomize_va_space =3D=3D 0 get_unmapped_area(TASK_SIZE - PAGE_SIZE) called by xol_add_vma() can not just return the "addr =3D=3D TASK_SIZE - PAGE_SIZE" hint, this addr is used by the stack vma. arch_get_unmapped_area_topdown() doesn't take TIF_ADDR32 into account and in_32bit_syscall() is false, this leads to info.high_limit > TASK_SIZE. vm_unmapped_area() happily returns the high address > TASK_SIZE and then get_unmapped_area() returns -ENOMEM after the "if (addr > TASK_SIZE - len)" check. handle_swbp() doesn't report this failure (probably it should) and silently restarts the probed insn. Endless loop. I think that the right fix should change the x86 get_unmapped_area() paths to rely on TIF_ADDR32 rather than in_32bit_syscall(). Note also that if CONFIG_X86_X32_ABI=3Dy, in_x32_syscall() falsely returns true in this case because ->orig_ax =3D -1. But we need a simple fix for -stable, so this patch just sets TS_COMPAT if the probed task is 32-bit to make in_ia32_syscall() true. Cc: stable@vger.kernel.org Reported-by: Paulo Andrade Link: https://lore.kernel.org/all/aV5uldEvV7pb4RA8@redhat.com/ Signed-off-by: Oleg Nesterov --- arch/x86/kernel/uprobes.c | 24 ++++++++++++++++++++++++ include/linux/uprobes.h | 1 + kernel/events/uprobes.c | 10 +++++++--- 3 files changed, 32 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index 7be8e361ca55..2dbd2e0691f7 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -1823,3 +1823,27 @@ bool is_uprobe_at_func_entry(struct pt_regs *regs) =20 return false; } + +#ifdef CONFIG_IA32_EMULATION +unsigned long __weak arch_uprobe_get_xol_area(void) +{ + struct thread_info *ti =3D current_thread_info(); + unsigned long vaddr; + + /* + * HACK: we are not in a syscall, but x86 get_unmapped_area() paths + * ignore TIF_ADDR32 and rely on in_32bit_syscall() to calculate + * vm_unmapped_area_info.high_limit. + * + * The #ifdef above doesn't cover the CONFIG_X86_X32_ABI=3Dy case, + * but in this case in_32bit_syscall() -> in_x32_syscall() always + * (falsely) returns true because ->orig_ax =3D=3D -1. + */ + if (test_thread_flag(TIF_ADDR32)) + ti->status |=3D TS_COMPAT; + vaddr =3D get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, PAGE_SIZE, 0, 0); + ti->status &=3D ~TS_COMPAT; + + return vaddr; +} +#endif diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h index ee3d36eda45d..f548fea2adec 100644 --- a/include/linux/uprobes.h +++ b/include/linux/uprobes.h @@ -242,6 +242,7 @@ extern void arch_uprobe_clear_state(struct mm_struct *m= m); extern void arch_uprobe_init_state(struct mm_struct *mm); extern void handle_syscall_uprobe(struct pt_regs *regs, unsigned long bp_v= addr); extern void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned lon= g vaddr); +extern unsigned long arch_uprobe_get_xol_area(void); #else /* !CONFIG_UPROBES */ struct uprobes_state { }; diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index f11ceb8be8c4..4e45236064dc 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -1694,6 +1694,12 @@ static const struct vm_special_mapping xol_mapping = =3D { .mremap =3D xol_mremap, }; =20 +unsigned long __weak arch_uprobe_get_xol_area(void) +{ + /* Try to map as high as possible, this is only a hint. */ + return get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, PAGE_SIZE, 0, 0); +} + /* Slot allocation for XOL */ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area) { @@ -1709,9 +1715,7 @@ static int xol_add_vma(struct mm_struct *mm, struct x= ol_area *area) } =20 if (!area->vaddr) { - /* Try to map as high as possible, this is only a hint. */ - area->vaddr =3D get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, - PAGE_SIZE, 0, 0); + area->vaddr =3D arch_uprobe_get_xol_area(); if (IS_ERR_VALUE(area->vaddr)) { ret =3D area->vaddr; goto fail; --=20 2.52.0