linux-kernel - Re: [PATCH v8 06/12] arm64/ptrace: Return early for ptrace_report_syscall

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Message-ID: <2cc2b342-d350-415d-bc5a-05aa3da17d50@arm.com>
Date: Thu, 27 Nov 2025 14:29:28 +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,
 charlie@...osinc.com, akpm@...ux-foundation.org, ldv@...ace.io,
 macro@...am.me.uk, deller@....de, mark.rutland@....com, efault@....de,
 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,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v8 06/12] arm64/ptrace: Return early for
 ptrace_report_syscall_entry() error

On 26/11/2025 08:14, Jinjie Ruan wrote:
> The generic entry abort the syscall_trace_enter() sequence if
> ptrace_report_syscall_entry() errors out, but arm64 not.
>
> As the ptrace_report_syscall_entry() comment said, the calling arch code
> should abort the system call and must prevent normal entry so no system
> call is made if ptrace_report_syscall_entry() return nonzero.

Which is already the case on arm64 before patch 2, which changes
syscall_trace_enter() so that it no longer returns regs->syscallno,
meaning that forget_syscall() no longer skips the syscall.

The most sensible thing to do is probably to move this patch before
patch 2. This ensures patch 2 doesn't introduce a regression, and then
the only effect of this patch is to abort the trace sequence early.

- Kevin

> In preparation for moving arm64 over to the generic entry code,
> return early if ptrace_report_syscall_entry() encounters an error.
>
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> ---
>  arch/arm64/kernel/ptrace.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index 233a7688ac94..da9687d30bcf 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -2346,15 +2346,18 @@ static inline unsigned long ptrace_save_reg(struct pt_regs *regs,
>  	return saved_reg;
>  }
>  
> -static void report_syscall_entry(struct pt_regs *regs)
> +static int report_syscall_entry(struct pt_regs *regs)
>  {
>  	unsigned long saved_reg;
> -	int regno;
> +	int regno, ret;
>  
>  	saved_reg = ptrace_save_reg(regs, PTRACE_SYSCALL_ENTER, &regno);
> -	if (ptrace_report_syscall_entry(regs))
> +	ret = ptrace_report_syscall_entry(regs);
> +	if (ret)
>  		forget_syscall(regs);
>  	regs->regs[regno] = saved_reg;
> +
> +	return ret;
>  }
>  
>  static void report_syscall_exit(struct pt_regs *regs)
> @@ -2380,9 +2383,11 @@ static void report_syscall_exit(struct pt_regs *regs)
>  
>  int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags)
>  {
> +	int ret;
> +
>  	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
> -		report_syscall_entry(regs);
> -		if (flags & _TIF_SYSCALL_EMU)
> +		ret = report_syscall_entry(regs);
> +		if (ret || (flags & _TIF_SYSCALL_EMU))
>  			return NO_SYSCALL;
>  	}
>