From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) (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 01AAD15C6 for ; Tue, 23 Jan 2024 04:00:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705982440; cv=none; b=ekrWEU9atC/FWTMM353kcNxRm36rZZEJHxoBR7hGOkGv/PYEFGqpVpCZRqUj0k5Nomfo59UsBUtL+Ohtj6GDHSz6mTuwoKp4ecTKNdQHFAzs/FAFiwBBv7m7OFIhDMzCleGrYxjB7xSIVz1qx/n4k52vJiO9fM0sxs4RtjdlZ5E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705982440; c=relaxed/simple; bh=HTux5BIIrgAHQKFYDFlexQlarUVDF1tSoVhHVafuXxk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XCNpNL2Qgq65chXiwg7dEyN9I1Md3VCqFzhY1Uu4XsD8fvjXuF0BYJq9wfrjsvWHNRvv8Zbu2OrG61SVpYKG50uWGYWcuBZiYjOhD7h4ZqEo6fjKB6QxXvAHYIyaQprF79qtVL62HupGiuWqKGPvpfeuNHYnbtkTpYqEQfHLZaA= 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=Bm1XLAAK; arc=none smtp.client-ip=95.215.58.187 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="Bm1XLAAK" Message-ID: <15d65e11-d957-4b03-bec3-0dcd58b50f97@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1705982436; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JA4VNi6lPEO0ZICt6dBnkKo/XOB/bUMthg+BctCwUxc=; b=Bm1XLAAKMEvSvDemIU6gUhClAonnXT67w/fiNGxXIPcgbAVK3rp+5sv/Tnwlp63HOvjlEq 9Nmkzk6IKsLu1kOf1GIKubHSZTb29PHEb7qHfssHboTr8j+yCOU0Mv31PUGbUDzHlx74PD boSChrGpZL96zpdtMMWcTwknaIKPGDE= Date: Mon, 22 Jan 2024 20:00:26 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH 43/82] bpf: Refactor intentional wrap-around test Content-Language: en-GB To: Kees Cook , linux-hardening@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Song Liu , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , bpf@vger.kernel.org, "Gustavo A. R. Silva" , Bill Wendling , Justin Stitt , linux-kernel@vger.kernel.org References: <20240122235208.work.748-kees@kernel.org> <20240123002814.1396804-43-keescook@chromium.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20240123002814.1396804-43-keescook@chromium.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 1/22/24 4:27 PM, Kees Cook wrote: > In an effort to separate intentional arithmetic wrap-around from > unexpected wrap-around, we need to refactor places that depend on this > kind of math. One of the most common code patterns of this is: > > VAR + value < VAR > > Notably, this is considered "undefined behavior" for signed and pointer > types, which the kernel works around by using the -fno-strict-overflow > option in the build[1] (which used to just be -fwrapv). Regardless, we > want to get the kernel source to the position where we can meaningfully > instrument arithmetic wrap-around conditions and catch them when they > are unexpected, regardless of whether they are signed[2], unsigned[3], > or pointer[4] types. > > Refactor open-coded wrap-around addition test to use add_would_overflow(). > This paves the way to enabling the wrap-around sanitizers in the future. > > Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] > Link: https://github.com/KSPP/linux/issues/26 [2] > Link: https://github.com/KSPP/linux/issues/27 [3] > Link: https://github.com/KSPP/linux/issues/344 [4] > Cc: Alexei Starovoitov > Cc: Daniel Borkmann > Cc: John Fastabend > Cc: Andrii Nakryiko > Cc: Martin KaFai Lau > Cc: Song Liu > Cc: Yonghong Song > Cc: KP Singh > Cc: Stanislav Fomichev > Cc: Hao Luo > Cc: Jiri Olsa > Cc: bpf@vger.kernel.org > Signed-off-by: Kees Cook > --- > kernel/bpf/verifier.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 65f598694d55..21e3f30c8757 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -12901,8 +12901,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, > dst_reg->smin_value = smin_ptr + smin_val; > dst_reg->smax_value = smax_ptr + smax_val; > } > - if (umin_ptr + umin_val < umin_ptr || > - umax_ptr + umax_val < umax_ptr) { > + if (add_would_overflow(umin_ptr, umin_val) || > + add_would_overflow(umax_ptr, umax_val)) { Maybe you could give a reference to the definition of add_would_overflow()? A link or a patch with add_would_overflow() defined cc'ed to bpf program. The patch itselfs looks good to me. > dst_reg->umin_value = 0; > dst_reg->umax_value = U64_MAX; > } else { > @@ -13023,8 +13023,8 @@ static void scalar32_min_max_add(struct bpf_reg_state *dst_reg, > dst_reg->s32_min_value += smin_val; > dst_reg->s32_max_value += smax_val; > } > - if (dst_reg->u32_min_value + umin_val < umin_val || > - dst_reg->u32_max_value + umax_val < umax_val) { > + if (add_would_overflow(umin_val, dst_reg->u32_min_value) || > + add_would_overflow(umax_val, dst_reg->u32_max_value)) { > dst_reg->u32_min_value = 0; > dst_reg->u32_max_value = U32_MAX; > } else { > @@ -13049,8 +13049,8 @@ static void scalar_min_max_add(struct bpf_reg_state *dst_reg, > dst_reg->smin_value += smin_val; > dst_reg->smax_value += smax_val; > } > - if (dst_reg->umin_value + umin_val < umin_val || > - dst_reg->umax_value + umax_val < umax_val) { > + if (add_would_overflow(umin_val, dst_reg->umin_value) || > + add_would_overflow(umax_val, dst_reg->umax_value)) { > dst_reg->umin_value = 0; > dst_reg->umax_value = U64_MAX; > } else {