From nobody Mon Jun 8 07:21:46 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 9D75C62809; Sun, 31 May 2026 16:58:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780246734; cv=none; b=WvUx4IkY1FfXVFVgKaIxsmbB/s6R6q5A2fitBcc+blouptdLELKQvU4kILCfswXzmCHT0gK46+E/ZZNF/oqH9sg2BkIA/DEjWut9RhdizkPWMYwXoJl24P3Ki4Dp6vorATgikxSeT3euPVn57jyvfOdXjPpq+SdtOjq/hQuB0Fo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780246734; c=relaxed/simple; bh=1Ou7HJkO3L14grfGDZqMSEBhaKT6ODVQdK2XDogdUV0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=G9J4hIuCSnue8coZcpKcn10ob8ddBhaRqkXQRupRw4gfAoy2Uo7wVYmbDbkeUd/mX/fx/38ZzKP9dXdd0TLo5wn3+xcgRg4yOTIRQSRaJYlDwKSWtioYu9wAb02PfDD7gIbL72d2J5b6yinKU3DfwNJK7F+ouxr+NQKv3hhyJDI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aSN+OMvp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="aSN+OMvp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 15CCF1F00893; Sun, 31 May 2026 16:58:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780246733; bh=4XCt6KVwLzptQOI3wbHQqErOB18s5I0OOfXV/KA+Rts=; h=From:To:Cc:Subject:Date; b=aSN+OMvpJNWqfqcHCr3+rxFW6fn52kxKo091Ma3hITkd5j4S+WCVEGoecvFilaS1S +Y2q4SpBBrK2I/cjUs9X4SaKpTQP8nEGxJ4ao4OFdolkwWfWGEwFJQlWPAzibxIvFU 6LoQptQYW7Oq6y2SY2TlONhz13QiO3AIf81H4siVcKGj2+yolg/40T4GrHpuKq11Tg nwuSDj9PFhkcPDoR6BN25dYwPJmGYVFBvTligqcw5VcNxhSkZepy3TqgPMnK6jxPdZ WZeE4p62xz7OmyHAej7Re/BXLyedapj8eK+HKugUtvIUg59gJxEuPdPdp4r7YTmP3T XYGJHq1PMTeNw== From: Tejun Heo To: ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev Cc: memxor@gmail.com, david@kernel.org, emil@etsalapatis.com, bpf@vger.kernel.org, sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next] bpf: Overwrite scratch PTE when allocating arena pages Date: Sun, 31 May 2026 06:58:52 -1000 Message-ID: <20260531165852.555930-1-tj@kernel.org> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" apply_range_set_cb() maps the pages for a new arena allocation. It returned -EBUSY when the target PTE was already populated. Kernel-fault recovery can leave the per-arena scratch page in an otherwise unallocated arena PTE: a BPF program that touched an unallocated address gets the scratch page installed there. A later bpf_arena_alloc_pages() covering that page then finds the PTE populated, returns -EBUSY, and leaves the scratch page in place. Every subsequent allocation of that page fails the same way. Drop the must-be-empty check so set_pte_at() installs the real page unconditionally, overwriting a scratch (or empty) PTE. Suggested-by: Alexei Starovoitov Signed-off-by: Tejun Heo Cc: David Hildenbrand --- kernel/bpf/arena.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) --- a/kernel/bpf/arena.c +++ b/kernel/bpf/arena.c @@ -131,15 +131,13 @@ static int apply_range_set_cb(pte_t *pte =20 if (!data) return 0; - /* sanity check */ - if (unlikely(!pte_none(ptep_get(pte)))) - return -EBUSY; =20 page =3D d->pages[d->i]; /* paranoia, similar to vmap_pages_pte_range() */ if (WARN_ON_ONCE(!pfn_valid(page_to_pfn(page)))) return -EINVAL; =20 + /* May be none or the scratch page, overwrite either way */ set_pte_at(&init_mm, addr, pte, mk_pte(page, PAGE_KERNEL)); d->i++; return 0;