linux-kernel - Re: [PATCH v7 02/11] arm64/ptrace: Refactor syscall_trace

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Message-ID: <4984d8e6-1431-4dcc-9723-c5470b5bcd49@arm.com>
Date: Tue, 18 Nov 2025 18:09:49 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>, catalin.marinas@....com,
 will@...nel.org, oleg@...hat.com, tglx@...utronix.de, peterz@...radead.org,
 luto@...nel.org, shuah@...nel.org, kees@...nel.org, wad@...omium.org,
 akpm@...ux-foundation.org, ldv@...ace.io, macro@...am.me.uk, deller@....de,
 mark.rutland@....com, song@...nel.org, mbenes@...e.cz, ryan.roberts@....com,
 ada.coupriediaz@....com, anshuman.khandual@....com, broonie@...nel.org,
 pengcan@...inos.cn, dvyukov@...gle.com, kmal@...k.li, lihongbo22@...wei.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v7 02/11] arm64/ptrace: Refactor
 syscall_trace_enter/exit()

On 17/11/2025 14:30, Jinjie Ruan wrote:
> [...]
>
> @@ -2386,19 +2384,27 @@ int syscall_trace_enter(struct pt_regs *regs)
>  	if (secure_computing() == -1)
>  		return NO_SYSCALL;
>  
> -	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
> -		trace_sys_enter(regs, regs->syscallno);
> +	/* Either of the above might have changed the syscall number */
> +	syscall = syscall_get_nr(current, regs);
> +
> +	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) {
> +		trace_sys_enter(regs, syscall);
>  
> -	audit_syscall_entry(regs->syscallno, regs->orig_x0, regs->regs[1],
> +		/*
> +		 * Probes or BPF hooks in the tracepoint may have changed the
> +		 * system call number as well.
> +		 */
> +		 syscall = syscall_get_nr(current, regs);
> +	}
> +
> +	audit_syscall_entry(syscall, regs->orig_x0, regs->regs[1],
>  			    regs->regs[2], regs->regs[3]);
>  
>  	return regs->syscallno;

It would be good to align the return with the generic version as well.

>  }
>  
> -void syscall_trace_exit(struct pt_regs *regs)
> +void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
>  {
> -	unsigned long flags = read_thread_flags();
> -
>  	audit_syscall_exit(regs);
>  
>  	if (flags & _TIF_SYSCALL_TRACEPOINT)
> diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
> index aba7ca6bca2d..6e3fe760e0bb 100644
> --- a/arch/arm64/kernel/syscall.c
> +++ b/arch/arm64/kernel/syscall.c
> @@ -124,7 +124,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
>  		 */
>  		if (scno == NO_SYSCALL)
>  			syscall_set_return_value(current, regs, -ENOSYS, 0);
> -		scno = syscall_trace_enter(regs);
> +		scno = syscall_trace_enter(regs, regs->syscallno, flags);

Nit: could use scno instead of regs->syscallno.

- Kevin

>  		if (scno == NO_SYSCALL)
>  			goto trace_exit;
>  	}
> @@ -143,7 +143,8 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
>  	}
>  
>  trace_exit:
> -	syscall_trace_exit(regs);
> +	flags = read_thread_flags();
> +	syscall_trace_exit(regs, flags);
>  }
>  
>  void do_el0_svc(struct pt_regs *regs)