From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794681869; b=DV2EFIJbrtuJQp+CKr2E6SHvzNiw/9m/+U9RMq/58Sqs78zJx7K/gvkdIrRd1s3SW6mX snworHcGZQPFvpGkTf4DeUB2aJskU2W1Pdtu0hSLGuqNqOdv3ZLRwS6PFn+YwroSsZc3S 6+3l/Nywvdg6l0Xfma/PLeg3aoIItsDMcIJGA6zx2+awi31jrM2QvQkcY+i0ioBH6SDmZ gjKBVEUfpMexf8DAa/Cn7zaHr3BOQl+uHuxQ7Sc5YYGv+GrPnaiSmYfX4Asc/Jy3IlWKv 1CfQlu9/jON/ueb2A+pPBHoGLl11sFXLdZlXxIZzJp5DWJ3+/7xwM75ukc7aKU1MLUA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794681869; h=Received:DKIM-Signature:Message-ID:From:Subject:Reply-To:To:Cc: In-Reply-To:References:Content-Type:Content-Transfer-Encoding:Date; bh=fr1dG/FFCTrWvTjxK8Y4u1acgGYTK2kcjlsb0UPgU7w=; b=2fvfrP/kn+vaa47i+Zfg1QLax186dOJC1M+DnaWNvDMgUQb0amg1Ord5QTjAS//sp1Cq 7st9fIG0DV2lhodYXe1vN/2jcPQB2m+ut40GT7XITgO1AnBUYDOy7oe8efYom/yzQt64S zqWLQKuB4K+PVPIqrQjb+M7083SXzJmT3m5fD883ybh2dkEjNiWLfEO1ROfUawtfrzOuz e1cjpyHo/WKHhCKczzWo3DUtx4bOTjGBLQmS1eY57Gf5Ui3kxb48mHguBXvOIbAaizaLW NzK7SFJUU4KMw2OdU4Qi+oxyATOoGHfQcDNXfy5/W5OlLY3GPxTMBvYwvwb3Lo+fYvA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=n+3TF2NJ; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C9D1606A32D for ; Sat, 14 Nov 2026 18:44:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=n+3TF2NJ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65ED31F000C4; Sat, 14 Nov 2026 18:44:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794681868; bh=fr1dG/FFCTrWvTjxK8Y4u1acgGYTK2kcjlsb0UPgU7w=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=n+3TF2NJkZC0DEFB93LwjpLdyrkGnk7BBvtocwsybWw0q20mxoJmFVx1zb17n/y36 ct0VU6LV0OLjv/JGecd7ej8B8QArvAtvHcKIs9QwlpYqFd7cTs00zRvxwXErzLR+05 DXs75Au2b49jbw5z5P3BgpAIZdE8fx8gwLY26vgisB869a9TdrDoHn/WNZCctxZHmS 3MAvBkJQijYrEK7kjSYJwXNK3VBrqX9rIBnpvEKuhpM4uusfEubzPCAagZTr4qWsQX ZVyu1hG7qzegzAGyJWgvHKaRNv/rE1/vsmi4XVluSmKu2OLmT0hQ0wJuvJisF9o6Re YFn23CS03BlZw== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH v11 2/3] ptrace: add PTRACE_SET_SYSCALL_INFO syscall skipping support Reply-To: sashiko-reviews@lists.linux.dev To: "Renzo Davoli" Cc: linux-s390@vger.kernel.org, "Heiko Carstens" , "Vasily Gorbik" , "Alexander Gordeev" , "Christian Borntraeger" In-Reply-To: <20261114181923.370930-3-renzo@cs.unibo.it> References: <20261114181923.370930-1-renzo@cs.unibo.it> <20261114181923.370930-3-renzo@cs.unibo.it> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Sat, 14 Nov 2026 18:44:27 +0000 X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Thank you for your contribution! Sashiko AI review found 1 potential issue to consider: - [High] ptrace: ptrace_set_syscall_info_seccomp_skip() breaks syscall skip on powerpc -- commit 18172201986e4a2acbcbbd3f1822583db8925569 Author: Renzo Davoli ptrace: add PTRACE_SET_SYSCALL_INFO syscall skipping support This commit extends PTRACE_SET_SYSCALL_INFO to allow a tracer to skip a system call at a PTRACE_SYSCALL_INFO_SECCOMP stop by changing the operation to PTRACE_SYSCALL_INFO_EXIT and specifying the return value. > diff --git a/kernel/ptrace.c b/kernel/ptrace.c > index 3f2fe68ccb140..ab6f5dab02238 100644 > --- a/kernel/ptrace.c > +++ b/kernel/ptrace.c [ ... ] > @@ -1119,12 +1128,35 @@ ptrace_set_syscall_info_exit(struct task_struct *= child, struct pt_regs *regs, > return 0; > } > =20 > +/* > + * Skip the system call at a PTRACE_SYSCALL_INFO_SECCOMP stop and set its > + * return value as specified by info->exit. > + * > + * The skip request is passed to seccomp out of band instead of by setti= ng > + * the system call number to -1: on some architectures the syscall numbe= r, > + * or the register seccomp reads it from, shares a register with the ret= urn > + * value, and on others -1 cannot be represented as a syscall number. > + */ > +static int > +ptrace_set_syscall_info_seccomp_skip(struct task_struct *child, > + struct pt_regs *regs, > + struct ptrace_syscall_info *info) > +{ > + int ret =3D ptrace_set_syscall_info_exit(child, regs, info); > + > + if (!ret) > + seccomp_ptrace_skip_syscall(child); > + > + return ret; > +} [Severity: High] Does calling ptrace_set_syscall_info_exit() from the tracer while the tracee is stopped at PTRACE_EVENT_SECCOMP break both the tracer and the tracee on powerpc? ptrace_set_syscall_info_exit() calls syscall_set_return_value(child, regs, ...), which on powerpc sets TIF_SYSCALL_RET on current rather than on task: arch/powerpc/include/asm/syscall.h:syscall_set_return_value() { ... /* * We are returning from the syscall, so anything that * depends on the regs being in the entry state is now invalid. */ set_thread_flag(TIF_SYSCALL_RET); } Because ptrace_set_syscall_info_seccomp_skip() runs in the tracer's task context, TIF_SYSCALL_RET is set on the tracer. On the tracer's next system call (such as PTRACE_GET_SYSCALL_INFO or PTRACE_CONT), system_call_exception() sees TIF_SYSCALL_RET set, clears it, and returns syscall_get_error(current, regs) (0) without executing the system call: arch/powerpc/kernel/syscall.c:system_call_exception() { ... if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0) || test_thread_flag(TIF_SYSCALL_RET))) { clear_thread_flag(TIF_SYSCALL_RET); return syscall_get_error(current, regs); } ... } In addition, when the tracee resumes from the skipped seccomp stop, syscall_enter_from_user_mode_randomize_stack() returns false and system_call_exception() returns syscall_get_error(current, regs), which syscall_exit_prepare() writes into regs->gpr[3]. When info->exit.is_error = is 0, syscall_get_error() returns 0, overwriting any non-error return value set by the tracer in regs->gpr[3]. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261114181923.3709= 30-1-renzo@cs.unibo.it?part=3D2