From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 23BA2379C46 for ; Tue, 21 Jul 2026 11:04:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784631854; cv=none; b=b1Wny65UVfzkLyiuowjUqZwMLmKGMjLihb1DUbxp2m4pN1laugnc3GGeO+YxWSL/EGbJLXYFgFdDnUhjgAVQqLJhZ7GqOx7R+EGSvCUY8IahMWXQ+eDK1QKWsUgmRGIh9mEIBCdYF9HE6Vif0ldHDpIDzU8FGqT0LXW/V3L4Mgw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784631854; c=relaxed/simple; bh=t5pjSKrGNSqWKvaNZ0EUjm3DHVQdnbw/NOq3yilEdes=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=I//Z9pyzFfN3RYGOBsO1hg/rfnPzrIHOXbRXl+wHRv72TZApPjKh0j12wVON8e75Aj3l1Q1mXA4cV9BJA4B+rUFr9+WAGlc8jNF82TN/xqOY3/xO9s5mSZaOAaNs5u/pW+ooO9P9Bc/UcihLY2lfENJRBP1uZ2xt7+0KcQlZVzs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de; spf=pass smtp.mailfrom=suse.de; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b=Rq1/Ng9C; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b=C+6C8oeG; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b=KNxOSiG2; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b=gmUuX1Z4; arc=none smtp.client-ip=195.135.223.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="Rq1/Ng9C"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="C+6C8oeG"; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="KNxOSiG2"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="gmUuX1Z4" Received: from kunlun.suse.cz (unknown [IPv6:2a07:de40:b306:2000::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (prime256v1) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 049A43E09; Tue, 21 Jul 2026 11:04:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1784631851; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QuE2qzP5TR2H8th0GJx8QRoWsG9NwmD+jXlWApIGZZk=; b=Rq1/Ng9CJRUBdCSMgOB6c7GxMYU1UpeKHnO18JcMkGVKM3cEVgobMqYJRZ1isJ3kKIfFQD XifpFuSACqV+WEfejfqA1XVXWlvPGZsyAoJIeBDO92kwI+JFIk/cRKoKNaBGztNbTSY/Cq AN4P4IK6H9730ExmJFkSpdAqSF3YlQg= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1784631851; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QuE2qzP5TR2H8th0GJx8QRoWsG9NwmD+jXlWApIGZZk=; b=C+6C8oeG7Gqhp2pv5ID5tV3mDvds64LQR+0ApKf7V9lAc1GN9G3GERp1gO74ASl/gZ1eqv 5U73v7fI0CiqUkBQ== Authentication-Results: smtp-out2.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=KNxOSiG2; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=gmUuX1Z4 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1784631850; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QuE2qzP5TR2H8th0GJx8QRoWsG9NwmD+jXlWApIGZZk=; b=KNxOSiG2vpe40bUpJxXcBeZMxsr9MONH0kVP5JTRk6hFgtQmFlD27QkL+AQV5aCUz6rBMQ cmPjpQWnzmKJ6HnpVW2DugjrFqhaj/q/rV8Mc6ur2UmnEA24U+497HXtZnZ/ZUdQ8labYP mn9dvEtGrvcqvckDZwbzvQE+TUVtR2g= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1784631850; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QuE2qzP5TR2H8th0GJx8QRoWsG9NwmD+jXlWApIGZZk=; b=gmUuX1Z4XRzsmYSWD/KHPQn1GCnIGlUut5ktm2znK0iZkaAf+hm/iUOHELL2TDOIz0GlFz X8Ws/8F3b16bz7Bg== Date: Tue, 21 Jul 2026 13:04:08 +0200 From: Michal =?iso-8859-1?Q?Such=E1nek?= To: Sven Schnelle Cc: Heiko Carstens , Vasily Gorbik , Alexander Gordeev , "H. Peter Anvin" , Thomas Gleixner , Christian Borntraeger , Peter Zijlstra , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] s390/syscall: Keep syscall return in extra ptregs member Message-ID: References: <20260715133830.2619853-1-svens@linux.ibm.com> <20260715133830.2619853-2-svens@linux.ibm.com> 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: <20260715133830.2619853-2-svens@linux.ibm.com> X-Spamd-Bar: +++++++++++++++ X-Rspamd-Queue-Id: 049A43E09 X-Spam-Flag: YES X-Spam-Score: 15.16 X-Spam-Level: *************** X-Rspamd-Action: add header X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spamd-Result: default: False [15.16 / 50.00]; SPAM_FLAG(5.00)[]; NEURAL_SPAM_LONG(3.50)[1.000]; BAYES_HAM(-3.00)[100.00%]; NEURAL_SPAM_SHORT(2.97)[0.989]; HFILTER_HOSTNAME_UNKNOWN(2.50)[]; RDNS_NONE(2.00)[]; ONCE_RECEIVED(1.20)[]; HFILTER_HELO_IP_A(1.00)[kunlun.suse.cz]; HFILTER_HELO_NORES_A_OR_MX(0.30)[kunlun.suse.cz]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FROM_HAS_DN(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b306:2000::2:from]; ARC_NA(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCVD_COUNT_ZERO(0.00)[0]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; MISSING_XM_UA(0.00)[]; RCPT_COUNT_SEVEN(0.00)[10]; DNSWL_BLOCKED(0.00)[2a07:de40:b306:2000::2:from]; TO_DN_SOME(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,kunlun.suse.cz:mid,kunlun.suse.cz:helo,infradead.org:email] X-Spam: Yes On Wed, Jul 15, 2026 at 03:38:29PM +0200, Sven Schnelle wrote: > On s390, both syscall number and return value share ptregs::gprs[2]. > Before executing the syscall, gpr[2] contains the syscall number, > and after execution it gets the return value assigned. > > This is problematic with tracing: When either seccomp or ptrace set > a return value and the syscall number to -1 to skip the syscall, the > return value will be overwritten. If the return value is positive, > it's impossible to determine that the syscall should be skipped. > > During conversion to generic entry a PIF_SYSCALL_RET_SET flag was > introduced which is set when syscall_set_return_value() is executed. > > Peter Zijlstra proposed in [1] to introduce a new member in ptregs > which keeps the return value and copy this to ptregs::gprs[2] before > exit to userspace instead. > > To avoid increasing ptregs size add it to the union which contains > int_parm_long and struct tpi_info as these members are not used during > syscalls. > > [1] https://lore.kernel.org/all/20260703105718.GO751831@noisy.programming.kicks-ass.net/ > > Suggested-by: Peter Zijlstra > Signed-off-by: Sven Schnelle > --- > arch/s390/include/asm/ptrace.h | 9 ++++++--- > arch/s390/include/asm/syscall.h | 5 ++--- > arch/s390/kernel/syscall.c | 15 +++------------ > 3 files changed, 11 insertions(+), 18 deletions(-) > > diff --git a/arch/s390/include/asm/ptrace.h b/arch/s390/include/asm/ptrace.h > index 495e310c3d6d..f39b349da9a7 100644 > --- a/arch/s390/include/asm/ptrace.h > +++ b/arch/s390/include/asm/ptrace.h > @@ -15,9 +15,8 @@ > > #define PIF_SYSCALL 0 /* inside a system call */ > #define PIF_PSW_ADDR_ADJUSTED 1 /* psw address has been adjusted */ > -#define PIF_SYSCALL_RET_SET 2 /* return value was set via ptrace */ > -#define PIF_GUEST_FAULT 3 /* indicates program check in sie64a */ > -#define PIF_FTRACE_FULL_REGS 4 /* all register contents valid (ftrace) */ > +#define PIF_GUEST_FAULT 2 /* indicates program check in sie64a */ > +#define PIF_FTRACE_FULL_REGS 3 /* all register contents valid (ftrace) */ > > #define _PIF_SYSCALL BIT(PIF_SYSCALL) > #define _PIF_ADDR_PSW_ADJUSTED BIT(PIF_PSW_ADDR_ADJUSTED) > @@ -130,6 +129,10 @@ struct pt_regs { > unsigned int int_parm; > unsigned long int_parm_long; > }; > + struct { > + unsigned long __unused; > + unsigned long syscall_ret; > + }; > struct tpi_info tpi_info; > }; > unsigned long flags; > diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h > index 4271e4169f45..22b6ed20a9ae 100644 > --- a/arch/s390/include/asm/syscall.h > +++ b/arch/s390/include/asm/syscall.h > @@ -52,15 +52,14 @@ static inline long syscall_get_error(struct task_struct *task, > static inline long syscall_get_return_value(struct task_struct *task, > struct pt_regs *regs) > { > - return regs->gprs[2]; > + return regs->syscall_ret; > } > > static inline void syscall_set_return_value(struct task_struct *task, > struct pt_regs *regs, > int error, long val) > { > - set_pt_regs_flag(regs, PIF_SYSCALL_RET_SET); > - regs->gprs[2] = error ? error : val; > + regs->syscall_ret = error ? error : val; > } > > static inline void syscall_get_arguments(struct task_struct *task, > diff --git a/arch/s390/kernel/syscall.c b/arch/s390/kernel/syscall.c > index 75d5a3cab14e..ce244dceec6d 100644 > --- a/arch/s390/kernel/syscall.c > +++ b/arch/s390/kernel/syscall.c > @@ -117,25 +117,16 @@ void noinstr __do_syscall(struct pt_regs *regs, int per_trap) > regs->int_code |= nr; > } > regs->gprs[2] = nr; > + regs->syscall_ret = -ENOSYS; > if (nr == __NR_restart_syscall && !(current->restart_block.arch_data & 1)) { > regs->psw.addr = current->restart_block.arch_data; > current->restart_block.arch_data = 1; > } > nr = syscall_enter_from_user_mode_work(regs, nr); > - /* > - * In the s390 ptrace ABI, both the syscall number and the return value > - * use gpr2. However, userspace puts the syscall number either in the > - * svc instruction itself, or uses gpr1. To make at least skipping syscalls > - * work, the ptrace code sets PIF_SYSCALL_RET_SET, which is checked here > - * and if set, the syscall will be skipped. > - */ > - if (unlikely(test_and_clear_pt_regs_flag(regs, PIF_SYSCALL_RET_SET))) > - goto out; > - regs->gprs[2] = -ENOSYS; > if (likely(nr < NR_syscalls)) { > nr = array_index_nospec(nr, NR_syscalls); > - regs->gprs[2] = sys_call_table[nr](regs); > + regs->syscall_ret = sys_call_table[nr](regs); > } > -out: > + regs->gprs[2] = regs->syscall_ret; > syscall_exit_to_user_mode(regs); Hello, I think this would break ptrace PTRACE_SETSIGINFO on syscall exit. It should use syscall_set_return_value but that now sets regs->syscall_ret, not regs->gprs[2]. At the same time the return value is in regs->gprs[2] at this point. Thanks Michal > } > -- > 2.53.0 >