linux-kernel - Re: [PATCH v2 6/7] ptrace: introduce PTRACE_SET_SYSCALL

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Message-ID: <20250115163809.GC11980@redhat.com>
Date: Wed, 15 Jan 2025 17:38:09 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: "Dmitry V. Levin" <ldv@...ace.io>
Cc: Eugene Syromyatnikov <evgsyr@...il.com>,
	Mike Frysinger <vapier@...too.org>,
	Renzo Davoli <renzo@...unibo.it>,
	Davide Berardi <berardi.dav@...il.com>,
	strace-devel@...ts.strace.io, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v2 6/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO request

Dmitry,

I can't review the non-x86 changes in 1/7 - 4/7.

As for this and the previous patch I see nothing bad after a quick glance.

Just I have some concerns about the "future extensions", I'll write another
email tomorrow. In particualar, I personally hate the very idea of
copy_struct_from_user/check_zeroed_user ;)

On 01/13, Dmitry V. Levin wrote:
>
> +ptrace_set_syscall_info_entry(struct task_struct *child, struct pt_regs *regs,
> +			      struct ptrace_syscall_info *info)
> +{
> +	unsigned long args[ARRAY_SIZE(info->entry.args)];
> +	int nr = info->entry.nr;
> +	int i;
> +
> +	if (nr != info->entry.nr)
> +		return -ERANGE;
> +
> +	for (i = 0; i < ARRAY_SIZE(args); i++) {
> +		args[i] = info->entry.args[i];
> +		if (args[i] != info->entry.args[i])
> +			return -ERANGE;
> +	}
> +
> +	syscall_set_nr(child, regs, nr);
> +	/*
> +	 * If the syscall number is set to -1, setting syscall arguments is not
> +	 * just pointless, it would also clobber the syscall return value on
> +	 * those architectures that share the same register both for the first
> +	 * argument of syscall and its return value.
> +	 */
> +	if (nr != -1)
> +		syscall_set_arguments(child, regs, args);

Thanks, much better than I tried to suggest in my reply to V1.

But may be

	if (syscall_get_nr() != -1)
		syscall_set_arguments(...);

will look a bit more consistent?

Oleg.