From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 197A32DFA41; Tue, 15 Apr 2025 17:09:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744736944; cv=none; b=ebBIBYEllMPTciR4CSOXzhdUupQHWf02Otzcxd8IHZhoG7si4Ozvt5u/8vY3KQi9vevAIKbhrKzLo4Qc9oMlEpyTv6iH4dUbMviJ4HCDlmoOzZ/3A3OJa2v2XJBPIS+ftmyGrR40PinPSk+wkEWbi3XxOg/gkjHtXbV9i/s26hk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744736944; c=relaxed/simple; bh=itV1mnPN2J4RD1cM9Wi9CevQGPk6e65bGfzsrCLdnyI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Yuxz5YZy02N6wBatVFEz+AeOm+JT0ZX4CICx+ioTVWejbFdNQC7I42zvUszoMM5Ggo98K63RDLZGJTjFl4+FW8Xd2fXR4L9Qj2d2aeSfnE7RLZeWgsDtYPza9Q2oZFvfNwt7UH9Q4y0tpI8beSpOQHC9aaH9uJDJuhJLGM+n77c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=awiPhOyH; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="awiPhOyH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 89079C4CEE9; Tue, 15 Apr 2025 17:09:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744736943; bh=itV1mnPN2J4RD1cM9Wi9CevQGPk6e65bGfzsrCLdnyI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=awiPhOyH4D5PZNFGlrG/oF3667wTf0iTqUMcdxjP2XQpyVdjWWa6MszBJStCuyU5x gMzY7aGsnU2vMwx2IbCMKC4RpUfIEz/xQgFMlDaJj28l6VbwpaJkAEHvBKFNiK1QUr x8tg2/iDdxXvw1Y13PKBrPmt3RYev/e8gu9gOMWNFjL9vqgbsVaX6Ah3SJKfejmbPx VuGrJbbMVSer4/bPjhdznI/i0wqcR/MXGFS/UHLtmR08FKtwNvM2w9cK4X6QER98cS RxtctKCNDvz0XXUztL855Oqhh1QOVp5EQJGLHt0afyVyUO6iABgJfPXZsO6R9awYhu IIT7Qbk3b+MJA== Date: Tue, 15 Apr 2025 10:09:00 -0700 From: Kees Cook To: Mostafa Saleh Cc: Andrew Morton , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-hardening@vger.kernel.org, elver@google.com, andreyknvl@gmail.com, ryabinin.a.a@gmail.com Subject: Re: [PATCH] lib/test_ubsan.c: Fix panic from test_ubsan_out_of_bounds Message-ID: <202504151006.19150DFE@keescook> References: <20250414213648.2660150-1-smostafa@google.com> <20250414170414.74f1c4e3542b1f10c8b24d90@linux-foundation.org> Precedence: bulk X-Mailing-List: linux-kernel@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: On Tue, Apr 15, 2025 at 08:48:30AM +0000, Mostafa Saleh wrote: > On Mon, Apr 14, 2025 at 05:04:14PM -0700, Andrew Morton wrote: > > On Mon, 14 Apr 2025 21:36:48 +0000 Mostafa Saleh wrote: > > > > > Running lib_ubsan.ko on arm64 (without CONFIG_UBSAN_TRAP) panics the > > > kernel > > > > > > [ 31.616546] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: test_ubsan_out_of_bounds+0x158/0x158 [test_ubsan] > > > [ 31.646817] CPU: 3 UID: 0 PID: 179 Comm: insmod Not tainted 6.15.0-rc2 #1 PREEMPT > > > [ 31.648153] Hardware name: linux,dummy-virt (DT) > > > [ 31.648970] Call trace: > > > [ 31.649345] show_stack+0x18/0x24 (C) > > > [ 31.650960] dump_stack_lvl+0x40/0x84 > > > [ 31.651559] dump_stack+0x18/0x24 > > > [ 31.652264] panic+0x138/0x3b4 > > > [ 31.652812] __ktime_get_real_seconds+0x0/0x10 > > > [ 31.653540] test_ubsan_load_invalid_value+0x0/0xa8 [test_ubsan] > > > [ 31.654388] init_module+0x24/0xff4 [test_ubsan] > > > [ 31.655077] do_one_initcall+0xd4/0x280 > > > [ 31.655680] do_init_module+0x58/0x2b4 > > > > > > That happens because the test corrupts other data in the stack: > > > 400: d5384108 mrs x8, sp_el0 > > > 404: f9426d08 ldr x8, [x8, #1240] > > > 408: f85f83a9 ldur x9, [x29, #-8] > > > 40c: eb09011f cmp x8, x9 > > > 410: 54000301 b.ne 470 // b.any > > > > > > As there is no guarantee the compiler will order the local variables > > > as declared in the module: > > > > argh. > > > > > volatile char above[4] = { }; /* Protect surrounding memory. */ > > > volatile int arr[4]; > > > volatile char below[4] = { }; /* Protect surrounding memory. */ > > > > > > So, instead of writing out-of-bound, we can read out-of-bound which > > > still triggers UBSAN but doesn't corrupt the stack. > > > > Would it be better to put the above three items into a struct, so we > > specify the layout? > > Yes, that also should work, but I ran into a panic because of another > problem, where the padding before and after the arr is 4 bytes, but > the index is "5", which is 8 bytes out of bound. > As we can only use 4/-1 as out of bounds. > That should also work: > > diff --git a/lib/test_ubsan.c b/lib/test_ubsan.c > index 8772e5edaa4f..4533e9cb52e6 100644 > --- a/lib/test_ubsan.c > +++ b/lib/test_ubsan.c > @@ -77,18 +77,18 @@ static void test_ubsan_shift_out_of_bounds(void) > > static void test_ubsan_out_of_bounds(void) > { > - volatile int i = 4, j = 5, k = -1; > - volatile char above[4] = { }; /* Protect surrounding memory. */ > - volatile int arr[4]; > - volatile char below[4] = { }; /* Protect surrounding memory. */ > - > - above[0] = below[0]; > + volatile int i = 4, j = 4, k = -1; > + struct { > + volatile char above[4]; /* Protect surrounding memory. */ > + volatile int arr[4]; > + volatile char below[4]; /* Protect surrounding memory. */ > + } data; Instead of all the volatiles, I recommend using: OPTIMIZER_HIDE_VAR(i); OPTIMIZER_HIDE_VAR(j); OPTIMIZER_HIDE_VAR(k); OPTIMIZER_HIDE_VAR(data); > UBSAN_TEST(CONFIG_UBSAN_BOUNDS, "above"); > - arr[j] = i; > + data.arr[j] = i; > > UBSAN_TEST(CONFIG_UBSAN_BOUNDS, "below"); > - arr[k] = i; > + data.arr[k] = i; > } > > enum ubsan_test_enum { > > --- > > I can send v2 with this approach if it's better. Yes please, the struct is the right solution to keep the memory contiguous. -- Kees Cook