From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (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 A65AE197A61 for ; Mon, 12 Aug 2024 18:26:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723487198; cv=none; b=c6TS+ZDPbDp9zkJdioZM6JtnIxML9HNEMzEMOuPCygH7hQJu3Yl3sEgiqHlx2i5gIO4fxTc9YVAA3Sb2wQoj3KWk4bUHSz5OWfyUDkSnt8StLhfuoYsHRH172a09m7qu7pKLFxRlMXe8LPAtU8QwlWJNZhyaDhRGt5lwg4YzCFY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723487198; c=relaxed/simple; bh=0WyGHkukyGZHDMwlvIezfC/2C4FqFjtsuDHqCt4AKt0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XwllkfTKEYIgsOo4mMme1kwvt47lT0K2ckcgJNEC4D2AtztXRS/SCfpM6TR2OcYKb/2bkn6/TuCwe7Zfm+Dzs/dEFJpR1Q5O1YRQfEOFqE/6E4A+BLz1Z7Il0mfdKVMg3qoHlCUOaPWcWUWsWDKvzw8GFzrbSt2zD619BIRAbJc= 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=aLPR3EiE; arc=none smtp.client-ip=91.218.175.173 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="aLPR3EiE" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1723487193; 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=4wKPHI7S780ej8n6HXdIRMab9YIG8QCPfjynVGg4Myo=; b=aLPR3EiEBKs+6qCEdqcFZQZhBmEW2Z3y3BcNc6uDWGKQoxyb0Oupi60c69+gHKGjE+jvrW 8zVfE+NyHj69TYEEAltVu0BbtfoHMsAE1jeSHc9hZuWXdC3saC7vxBNDDOjGcPorau/YK9 THOmvZQEFDLxtDqmB6epk5HhSOxWHo4= Date: Mon, 12 Aug 2024 11:26:27 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf 1/2] bpf: Fix a kernel verifier crash in stacksafe() Content-Language: en-GB To: Alexei Starovoitov , Eduard Zingerman Cc: bpf , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Kernel Team , Martin KaFai Lau , Daniel Hodges References: <20240812052106.3980303-1-yonghong.song@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 8/12/24 10:50 AM, Alexei Starovoitov wrote: > On Mon, Aug 12, 2024 at 10:47 AM Eduard Zingerman wrote: >> On Mon, 2024-08-12 at 10:44 -0700, Alexei Starovoitov wrote: >> >> [...] >> >>> Should we move the check up instead? >>> >>> if (i >= cur->allocated_stack) >>> return false; >>> >>> Checking it twice looks odd. >> A few checks before that, namely: >> >> if (!(old->stack[spi].spilled_ptr.live & REG_LIVE_READ) >> && exact == NOT_EXACT) { >> i += BPF_REG_SIZE - 1; >> /* explored state didn't use this */ >> continue; >> } >> >> if (old->stack[spi].slot_type[i % BPF_REG_SIZE] == STACK_INVALID) >> continue; >> >> if (env->allow_uninit_stack && >> old->stack[spi].slot_type[i % BPF_REG_SIZE] == STACK_MISC) >> continue; >> >> Should be done regardless cur->allocated_stack. > Right, but then let's sink old->slot_type != cur->slot_type down? We could do the following to avoid double comparison: diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index df3be12096cf..1906798f1a3d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -17338,10 +17338,13 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old, */ for (i = 0; i < old->allocated_stack; i++) { struct bpf_reg_state *old_reg, *cur_reg; + bool cur_exceed_bound; spi = i / BPF_REG_SIZE; - if (exact != NOT_EXACT && + cur_exceed_bound = i >= cur->allocated_stack; + + if (exact != NOT_EXACT && !cur_exceed_bound && old->stack[spi].slot_type[i % BPF_REG_SIZE] != cur->stack[spi].slot_type[i % BPF_REG_SIZE]) return false; @@ -17363,7 +17366,7 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old, /* explored stack has more populated slots than current stack * and these slots were used */ - if (i >= cur->allocated_stack) + if (cur_exceed_bound) return false; /* 64-bit scalar spill vs all slots MISC and vice versa. WDYT?