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 4C31B101CA; Sat, 16 Mar 2024 10:41:46 +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=1710585706; cv=none; b=GUMsVxtz6nqaKEK5L/34LoGaUOdmcRVu4wKHXnzTob0mJg5PGjFjX17ERTuDOrb47rG0wv2a0lFpbhkU/rD/e5HQaiUrqgVxSTRUpV5TVnaLPKytSvvHBNAS6Pii+wYs1k+71+NFqNg/u/y/mJAESzcMT0rwSajZGtIFRubeO28= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710585706; c=relaxed/simple; bh=VvZZEADe/yjZo+gK5HdF8YmkQc3//fHA5cwRHHUoupI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nvnGIPqLUuV5gboz7j1xwNPcxoIP8S8gpkG+WHIaewi7jxV9LZro/e9HrsZR+qp0bJ+1+6JnLSXTSiS0lrS3e/zWjsM3OFpyIIRMYHBzJeUoVpk1Q39VDLuT6r4LTnqj9MrY86m59evj+cadk6mpkHfUr06MmQ7I/D8ul2tXFFc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fFlut+ct; 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="fFlut+ct" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 833DBC43390; Sat, 16 Mar 2024 10:41:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1710585705; bh=VvZZEADe/yjZo+gK5HdF8YmkQc3//fHA5cwRHHUoupI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fFlut+ctJhF18SbVxoUKwpANag+xrSwhU4G9rzBfcB0QYShA86thiC3nc5Glm6yzq A88I4dyu6EpFFc8MMNgOBgiANqAFQIqzt6dw+PzuWfk9uT8DboNr5Ih3+pL8hGk/0D 3kHEf9bn8jWAH7JvcO9+qkhyUAmJ/fASoargC3F9Pw6Byx2fDKF2jZ1HEyo66zNDBI daOHh4ZSSgtJcV+tmA9SRNQqI61WB95M1UOnt3aFf7MEuMpheEfpfOcnVxXkpzjfCm zL7tzMHLggeBLsxDCdKG1CO2sGIYvE83Pxej0LgKljGElw+pv3f0GbADAT3iUzBhjb pHQRVRZR8i5DQ== Date: Sat, 16 Mar 2024 06:41:44 -0400 From: Sasha Levin To: Johan Hovold Cc: stable@vger.kernel.org, Bjorn Andersson , Konrad Dybcio , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Dmitry Baryshkov Subject: Re: [PATCH stable-6.7] soc: qcom: pmic_glink_altmode: fix drm bridge use-after-free Message-ID: References: <20240308090357.8758-1-johan+linaro@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20240308090357.8758-1-johan+linaro@kernel.org> On Fri, Mar 08, 2024 at 10:03:57AM +0100, Johan Hovold wrote: >commit b979f2d50a099f3402418d7ff5f26c3952fb08bb upstream. > >A recent DRM series purporting to simplify support for "transparent >bridges" and handling of probe deferrals ironically exposed a >use-after-free issue on pmic_glink_altmode probe deferral. > >This has manifested itself as the display subsystem occasionally failing >to initialise and NULL-pointer dereferences during boot of machines like >the Lenovo ThinkPad X13s. > >Specifically, the dp-hpd bridge is currently registered before all >resources have been acquired which means that it can also be >deregistered on probe deferrals. > >In the meantime there is a race window where the new aux bridge driver >(or PHY driver previously) may have looked up the dp-hpd bridge and >stored a (non-reference-counted) pointer to the bridge which is about to >be deallocated. > >When the display controller is later initialised, this triggers a >use-after-free when attaching the bridges: > > dp -> aux -> dp-hpd (freed) > >which may, for example, result in the freed bridge failing to attach: > > [drm:drm_bridge_attach [drm]] *ERROR* failed to attach bridge /soc@0/phy@88eb000 to encoder TMDS-31: -16 > >or a NULL-pointer dereference: > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 > ... > Call trace: > drm_bridge_attach+0x70/0x1a8 [drm] > drm_aux_bridge_attach+0x24/0x38 [aux_bridge] > drm_bridge_attach+0x80/0x1a8 [drm] > dp_bridge_init+0xa8/0x15c [msm] > msm_dp_modeset_init+0x28/0xc4 [msm] > >The DRM bridge implementation is clearly fragile and implicitly built on >the assumption that bridges may never go away. In this case, the fix is >to move the bridge registration in the pmic_glink_altmode driver to >after all resources have been looked up. > >Incidentally, with the new dp-hpd bridge implementation, which registers >child devices, this is also a requirement due to a long-standing issue >in driver core that can otherwise lead to a probe deferral loop (see >commit fbc35b45f9f6 ("Add documentation on meaning of -EPROBE_DEFER")). > >[DB: slightly fixed commit message by adding the word 'commit'] >Fixes: 080b4e24852b ("soc: qcom: pmic_glink: Introduce altmode support") >Fixes: 2bcca96abfbf ("soc: qcom: pmic-glink: switch to DRM_AUX_HPD_BRIDGE") >Cc: # 6.3 >Cc: Bjorn Andersson >Cc: Dmitry Baryshkov >Signed-off-by: Johan Hovold >Reviewed-by: Bjorn Andersson >Reviewed-by: Dmitry Baryshkov >Signed-off-by: Dmitry Baryshkov >Link: https://patchwork.freedesktop.org/patch/msgid/20240217150228.5788-4-johan+linaro@kernel.org >[ johan: backport to 6.7 which does not have DRM aux bridge ] >Signed-off-by: Johan Hovold Queued up, thanks! -- Thanks, Sasha