From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-185.mta0.migadu.com (out-185.mta0.migadu.com [91.218.175.185]) (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 4A1F036A35C for ; Tue, 12 May 2026 03:29:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.185 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778556588; cv=none; b=Q9w+ro+x2ghX78VLqoJlIdrB9xGq17RP+P6zpTzJciZHta9fteVfb46BIqy87FLqqCbovYZ5cFEp90gVwhsCrwikaC66FMyf7Ph/oYNzuibdnkf+5ZCsjv5UJlT0Q7Yuq6mQ5YI0YtWuWYI0bSDZrRh1NHxAPhm6QSMkXyva9gE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778556588; c=relaxed/simple; bh=9ysmXqcq6yywIVEXg3qZmzNnV0dO0flBjGmZ5AWDRwc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=goaDleAw2vDelUB6Y65YZhRFyaj5co5UvBczlm6iixEZ1j+d8xySNkNYT8K1wcwwnOWCzVs7WRJD0MCF1r2KliuxFhmG/1MZwuLW3IV6tDl5QB0i4BU4nNa6ESgbHsdVZl0mYqmJVwthEMWnsCSj+b8PwKQEDUO1hGw0aysYQAY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=QlF5DRK2; arc=none smtp.client-ip=91.218.175.185 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="QlF5DRK2" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778556585; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=vj8tMsyX4vmxJRdOYM1l8iq31iyGWVIESSJoDNB31qk=; b=QlF5DRK2MiSbOtCXwqyUooWQNRlS0BDUEtW27BdpqOY48D3Z8JOLq7xRgCJgPqxeEgStDm bYaKaRQ+mnjyabg7mblITS5+AvYcibnItBSMhWwlJmwwkw05OS2gl1v/kQ5NtdTVW9u8xr zFoPXm2QjBd/BrU5/iNFq1ud7zey2aM= From: Ihor Solodrai To: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Eduard Zingerman , Kumar Kartikeya Dwivedi Cc: Puranjay Mohan , Shakeel Butt , Mykyta Yatsenko , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH bpf v3 2/3] bpf: Avoid faultable build ID reads under mm locks Date: Mon, 11 May 2026 20:29:05 -0700 Message-ID: <20260512032906.2670326-3-ihor.solodrai@linux.dev> In-Reply-To: <20260512032906.2670326-1-ihor.solodrai@linux.dev> References: <20260512032906.2670326-1-ihor.solodrai@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Sleepable build ID parsing can block in __kernel_read() [1], so the stackmap sleepable path must not call it while holding mmap_lock or a per-VMA read lock. The issue and the fix are conceptually similar to a recent procfs patch [2]. Resolve each covered VMA with a stable read-side reference, preferring lock_vma_under_rcu() and falling back to mmap_read_trylock() only long enough to acquire the VMA read lock. Take a reference to the backing file, drop the VMA lock, and then parse the build ID through (sleepable) build_id_parse_file(). [1]: https://lore.kernel.org/all/20251218005818.614819-1-shakeel.butt@linux.dev/ [2]: https://lore.kernel.org/all/20260128183232.2854138-1-andrii@kernel.org/ Fixes: 777a8560fd29 ("lib/buildid: use __kernel_read() for sleepable context") Assisted-by: Codex:gpt-5.4 Suggested-by: Puranjay Mohan Signed-off-by: Ihor Solodrai --- kernel/bpf/stackmap.c | 105 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 105 insertions(+) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 4ef0fd06cea5..c1e96df360c3 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -9,6 +9,7 @@ #include #include #include +#include #include "percpu_freelist.h" #include "mmap_unlock_work.h" @@ -158,6 +159,105 @@ static inline void stack_map_build_id_set_ip(struct bpf_stack_build_id *id) memset(id->build_id, 0, BUILD_ID_SIZE_MAX); } +struct stack_map_vma_lock { + bool vma_locked; + struct vm_area_struct *vma; + struct mm_struct *mm; +}; + +static struct vm_area_struct * +stack_map_lock_vma(struct stack_map_vma_lock *lock, unsigned long ip) +{ + struct mm_struct *mm = lock->mm; + struct vm_area_struct *vma; + + if (WARN_ON_ONCE(!mm)) + return NULL; + + vma = lock_vma_under_rcu(mm, ip); + if (vma) + goto vma_locked; + + if (!mmap_read_trylock(mm)) + return NULL; + + vma = vma_lookup(mm, ip); + if (!vma) { + mmap_read_unlock(mm); + return NULL; + } + +#ifdef CONFIG_PER_VMA_LOCK + if (!vma_start_read_locked(vma)) { + mmap_read_unlock(mm); + return NULL; + } + mmap_read_unlock(mm); +#else + mmap_read_unlock(mm); + return NULL; +#endif +vma_locked: + lock->vma_locked = true; + lock->vma = vma; + return vma; +} + +static void stack_map_unlock_vma(struct stack_map_vma_lock *lock) +{ + struct vm_area_struct *vma = lock->vma; + + if (lock->vma_locked) { + if (WARN_ON_ONCE(!vma)) + goto out; + vma_end_read(vma); + } +out: + lock->vma_locked = false; + lock->vma = NULL; +} + +static void stack_map_get_build_id_offset_sleepable(struct bpf_stack_build_id *id_offs, + u32 trace_nr) +{ + struct mm_struct *mm = current->mm; + struct stack_map_vma_lock lock = { + .vma_locked = false, + .vma = NULL, + .mm = mm, + }; + unsigned long vm_pgoff, vm_start; + struct vm_area_struct *vma; + struct file *file; + u64 ip; + + for (u32 i = 0; i < trace_nr; i++) { + ip = READ_ONCE(id_offs[i].ip); + vma = stack_map_lock_vma(&lock, ip); + if (!vma || !vma->vm_file) { + stack_map_build_id_set_ip(&id_offs[i]); + stack_map_unlock_vma(&lock); + continue; + } + + file = get_file(vma->vm_file); + vm_pgoff = vma->vm_pgoff; + vm_start = vma->vm_start; + stack_map_unlock_vma(&lock); + + /* build_id_parse_file() may block on filesystem reads */ + if (build_id_parse_file(file, id_offs[i].build_id, NULL)) { + stack_map_build_id_set_ip(&id_offs[i]); + fput(file); + continue; + } + fput(file); + + id_offs[i].offset = (vm_pgoff << PAGE_SHIFT) + ip - vm_start; + id_offs[i].status = BPF_STACK_BUILD_ID_VALID; + } +} + /* * Expects all id_offs[i].ip values to be set to correct initial IPs. * They will be subsequently: @@ -178,6 +278,11 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, const char *prev_build_id; int i; + if (may_fault && has_user_ctx) { + stack_map_get_build_id_offset_sleepable(id_offs, trace_nr); + return; + } + /* If the irq_work is in use, fall back to report ips. Same * fallback is used for kernel stack (!user) on a stackmap with * build_id. -- 2.54.0