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Mon, 2 Mar 2026 15:40:47 +0000 (GMT) Date: Mon, 2 Mar 2026 16:40:45 +0100 From: Vasily Gorbik To: Heiko Carstens Cc: Alexander Gordeev , Sven Schnelle , Christian Borntraeger , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Subject: Re: [PATCH 3/3] s390/stackleak: Fix __stackleak_poison() inline assembly constraint Message-ID: References: <20260302133500.1560531-1-hca@linux.ibm.com> <20260302133500.1560531-4-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260302133500.1560531-4-hca@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: Zse6fxysxo_0ZaexxLTmCtZdcjDiihm- X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzAyMDEzMSBTYWx0ZWRfX7RxJKQm8VwTK IEOaRexFuIAnpW6n11Eok8hijBPy4Eas1VGnZyvhmpkNwbsce4gciCntmIR6wXIE46GK1bGqj5e UnYeWtqAsoJjFiatewv04Pxtrx4JAQF8iKj5rX4++pahvxyux9QL9pu/3ZxV89xe8JDd5Rt/rcQ ey8Gf4n6Wc/jjpce8VotQfCPEEBokZ/M1a6cJ8atVEEpbrvn4tqdE8y2lfiAfiuuorON9t8xuwz 3sLkqmrZRehzMRJqxJ+X+HyV/7IuODRTIPAzcgY1/pQ0tEKY9cW6NAyqeRHW9cWSqT/h/LD7DNy P6syf07W2fkWDV5Jr1ZdCAyacg8Usu+EO71v71UuN/iw0uKsuRHO2dOuCgTWvKh+vhnUiQW23U9 F+YO7OpOlvrMlsjf4g5tDUG/ROIYkBQi/nxJExCfAjmPh26zXFPFKRAuVwcPjuQq3UQUev2hmMM jp3771Os+0bYfQwu1ug== X-Authority-Analysis: v=2.4 cv=csCWUl4i c=1 sm=1 tr=0 ts=69a5af84 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=2bjmQ6Ql1u0Qu4szMpgA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: Zse6fxysxo_0ZaexxLTmCtZdcjDiihm- X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-02_03,2026-03-02_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 priorityscore=1501 suspectscore=0 malwarescore=0 adultscore=0 clxscore=1011 bulkscore=0 phishscore=0 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603020131 On Mon, Mar 02, 2026 at 02:35:00PM +0100, Heiko Carstens wrote: > The __stackleak_poison() inline assembly comes with a "count" operand where > the "d" constraint is used. "count" is used with the exrl instruction and > "d" means that the compiler may allocate any register from 0 to 15. > > If the compiler would allocate register 0 then the exrl instruction would > not or the value of "count" into the executed instruction - resulting in a > stackframe which is only partially poisoned. > > Use the correct "a" constraint, which excludes register 0 from register > allocation. > > Fixes: 2a405f6bb3a5 ("s390/stackleak: provide fast __stackleak_poison() implementation") > Cc: stable@vger.kernel.org > Signed-off-by: Heiko Carstens > --- > arch/s390/include/asm/processor.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Reviewed-by: Vasily Gorbik