From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f53.google.com (mail-wm1-f53.google.com [209.85.128.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A65D638CFF5 for ; Fri, 27 Mar 2026 20:42:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.53 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774644122; cv=none; b=b3AHMjJYXXWfz3VHxhRL2vu66bIlVkNnWb1UTO6X6SMH1rpVrUEqXHsM8K1WTX9kvADlJmmeTBTFyPCaq43VM5lPo1Y9n6xME3+PdzLlUto2PkFSna6PwKgIEaDH7egtbLTsbgjSnCiKTcNiyeWunhyoROe9SrPadlJ2KKwBvsw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774644122; c=relaxed/simple; bh=OseZgolmzhAr4jFqxBRNN1L/7ggRloDkt++YOQpR2p8=; h=From:Date:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=U9q+p9fff2LcrY/GmJbZrxgxxJlVUmDr317kiM886itzd6yXP2HmPjX7f2Znas+CUWXcCM5vHj9cjDa+Lu5B/LWn/zicfleQKQ/BXx8hyD7Gq0IMu4/bx0w+Iix4bnWHzorcjLUI76b6xIgIs7GxuI+oiTixxMkKT+f6hl5VT/E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=nM/BfZ+Y; arc=none smtp.client-ip=209.85.128.53 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="nM/BfZ+Y" Received: by mail-wm1-f53.google.com with SMTP id 5b1f17b1804b1-4838c15e3cbso20746135e9.3 for ; Fri, 27 Mar 2026 13:42:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1774644119; x=1775248919; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:from:to:cc:subject:date:message-id:reply-to; bh=sZ/7XD1rJXQYlW2CUYI9bsXyEYg+8UaYCRyEmTmJK34=; b=nM/BfZ+YLMVvk5P3x54GwdFqdhKmNJ1Hx2r4zooAmkk5jyqty65BG5Z/uNElRCb6iY atigMkijN16Bg0MggWKJdpuEJizIgzzsHp8uWkf3jKGObwBow5TmIAnkXXrqS59Y+HyE hUaDJeb7L7MvoygWrNTlThnWgcILNdnwFIxHBmdrUObxwmUefmvY23WjhAsY3hLEmf3V rONqyr8uPLBAQt0hOQm9zA/WPdl8mxXYOXcdgzOLm3g5YAip4rEMTMXdKxwYDbKtdNF+ 59EkTsbwaWxSa4pz4TXedRnJ3xpRtQwB741vQE2mzx7GXYus9zCyOz5xX/f6uYz16fe6 I6QQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774644119; x=1775248919; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=sZ/7XD1rJXQYlW2CUYI9bsXyEYg+8UaYCRyEmTmJK34=; b=ZYgddooMe2FLxOGFYiMn0RP/0X69yfVW1wgArH5sx+PwmtFQ+iVPeHRHWBDTEZQvMB +pierlRj108zo9kecip056YcyAYwe9D4omBssfYLwo0W9DDfHN2QvVG+NywtPGBQg5If vYEscQb9+VZSQNbm2kYE78sfT3hboMndNFf5U28FrdNXZldFJQUkeQ55/7TlyDfcyw/D o9LXtGKU0OeyPAo8cEf5BUjVC+b6rSP7X+sBAAuObxlj7uHwYhsUWRD7v1v5meZrP+iH s2qZ0uWlCD5nkp3GSZz/fo39c7N/EoaOnIdQSoys4Gt4z+X2ltymaEYqSkIWu0HoMzZe I+yg== X-Forwarded-Encrypted: i=1; AJvYcCVIdJpIRQyKnpJnF0jwPzxlS9Iyzi6VyyU1D5aljuvgnccp9ArscNIfNzLQ0DbBQV+Ffn/4poE=@vger.kernel.org X-Gm-Message-State: AOJu0YyzVSjIHXwhS+GVQCVBxnSMC+1hULkhi3sjwxl+C8enPgtWd5Vx dfOufOKQSSfxURIK4vO+6OdX4AIS6mqZBRRelzy+izffc+aUBAy0QPIE X-Gm-Gg: ATEYQzxWwjj2im4bIAEpevmRvB5GMjpUqp7ubNZmYjKOC/Ax2c7Dgt/Fl4tbqQ0SM5y 7cZz60Hf3/oQCQ6FAeCDlW0Cy7MOAZI1GUPxSXo0qtkUTH2Rn6W4/qUQWoMhSjKO8lCNn+DZtrs IDO177nCSQgpIvzj/k0oBby2VWaH5pKgWD2nS0IQwY0lWcf/EzOn+AGmMzkvchCnVXNBA9ljBiO 2l0aG2e12WSNaBVgzD/8NicIyF8WMPnEtEqq6TxM1JQozZeg73bVYvWxj3JGNmPH1e5iuJCzXSY c2GkKZKqOPhc51Zb2nlAnDKwyNiLYHH/LUYR7vpDt5QGDNXHLTADeS2kB3rn4AeupnkI0xHh09h pqfW2N2f7LIYmechgpFkpR9sNAK2SdOA5/Q8lBDxf1kPpXiP5xUeGKupzAnqcvNLkt42BzIB0tB KFsK04MmpfMKbr/bLIuck0dzLxFy3jl6ClfcFiltK9PI9oGU16pwekWJ9LGw== X-Received: by 2002:a05:600c:1d15:b0:485:2fc5:3a5 with SMTP id 5b1f17b1804b1-48727edf4f5mr64539105e9.26.1774644118896; Fri, 27 Mar 2026 13:41:58 -0700 (PDT) Received: from krava (cust-west-par-46-193-1-135.cust.wifirst.net. [46.193.1.135]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4872712b3ebsm20378445e9.19.2026.03.27.13.41.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Mar 2026 13:41:58 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Fri, 27 Mar 2026 21:41:56 +0100 To: Leon Hwang Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Shuah Khan , "David S . Miller" , Jakub Kicinski , Jesper Dangaard Brouer , Toke Hoiland-Jorgensen , Lorenzo Bianconi , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, netdev@vger.kernel.org, kernel-patches-bot@fb.com Subject: Re: [PATCH bpf-next 2/3] bpf: Disallow freplace on kprobe with mismatched kprobe_write_ctx values Message-ID: References: <20260324150444.68166-1-leon.hwang@linux.dev> <20260324150444.68166-3-leon.hwang@linux.dev> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260324150444.68166-3-leon.hwang@linux.dev> On Tue, Mar 24, 2026 at 11:04:43PM +0800, Leon Hwang wrote: > uprobe programs are allowed to modify struct pt_regs. > > Since the actual program type of uprobe is KPROBE, it can be abused to > modify struct pt_regs via kprobe+freplace when the kprobe attaches to > kernel functions. > > For example, > > SEC("?kprobe") > int kprobe(struct pt_regs *regs) > { > return 0; > } > > SEC("?freplace") > int freplace_kprobe(struct pt_regs *regs) > { > regs->di = 0; > return 0; > } > > freplace_kprobe prog will attach to kprobe prog. > kprobe prog will attach to a kernel function. > > Without this patch, when the kernel function runs, its first arg will > always be set as 0 via the freplace_kprobe prog. > > To avoid the abuse of kprobe_write_ctx=true via kprobe+freplace, disallow > freplace on kprobe programs with mismatched kprobe_write_ctx values. > > Fixes: 7384893d970e ("bpf: Allow uprobe program to change context registers") > Signed-off-by: Leon Hwang > --- > kernel/bpf/verifier.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 12330466d58b..f8257bae6081 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -6404,6 +6404,14 @@ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off, > /* remember the offset of last byte accessed in ctx */ > if (env->prog->aux->max_ctx_offset < off + size) > env->prog->aux->max_ctx_offset = off + size; > + if (env->prog->type == BPF_PROG_TYPE_EXT) { > + struct bpf_prog *dst_prog = env->prog->aux->dst_prog; > + > + if (env->prog->aux->kprobe_write_ctx != dst_prog->aux->kprobe_write_ctx) { > + verbose(env, "Extension program cannot have different kprobe_write_ctx value with target prog\n"); > + return -EINVAL; > + } > + } would it be more clear to check this in bpf_check_attach_target, instead of depending on actual write to context jirka