Re: [PATCH 3/6] syscall.h: introduce syscall_set_nr()

From: Sven Schnelle <svens@linux.ibm.com>
To: "Dmitry V. Levin" <ldv@strace.io>
Cc: Oleg Nesterov <oleg@redhat.com>,
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Subject: Re: [PATCH 3/6] syscall.h: introduce syscall_set_nr()
Date: Fri, 10 Jan 2025 08:37:46 +0100	[thread overview]
Message-ID: <yt9dzfjz6rw5.fsf@linux.ibm.com> (raw)
In-Reply-To: <20250107230438.GC30633@strace.io> (Dmitry V. Levin's message of "Wed, 8 Jan 2025 01:04:38 +0200")

"Dmitry V. Levin" <ldv@strace.io> writes:

> Similar to syscall_set_arguments() that complements
> syscall_get_arguments(), introduce syscall_set_nr()
> that complements syscall_get_nr().
>
> syscall_set_nr() is going to be needed along with
> syscall_set_arguments() on all HAVE_ARCH_TRACEHOOK
> architectures to implement PTRACE_SET_SYSCALL_INFO API.
>
> Signed-off-by: Dmitry V. Levin <ldv@strace.io>
> ---
>  arch/arc/include/asm/syscall.h        |  6 ++++++
>  arch/arm/include/asm/syscall.h        | 12 ++++++++++++
>  arch/arm64/include/asm/syscall.h      |  7 +++++++
>  arch/hexagon/include/asm/syscall.h    |  7 +++++++
>  arch/loongarch/include/asm/syscall.h  |  7 +++++++
>  arch/m68k/include/asm/syscall.h       |  7 +++++++
>  arch/microblaze/include/asm/syscall.h |  7 +++++++
>  arch/mips/include/asm/syscall.h       |  7 +++++++
>  arch/nios2/include/asm/syscall.h      |  5 +++++
>  arch/openrisc/include/asm/syscall.h   |  6 ++++++
>  arch/parisc/include/asm/syscall.h     |  7 +++++++
>  arch/powerpc/include/asm/syscall.h    |  5 +++++
>  arch/riscv/include/asm/syscall.h      |  7 +++++++
>  arch/s390/include/asm/syscall.h       |  7 +++++++
>  arch/sh/include/asm/syscall_32.h      |  7 +++++++
>  arch/sparc/include/asm/syscall.h      |  7 +++++++
>  arch/um/include/asm/syscall-generic.h |  5 +++++
>  arch/x86/include/asm/syscall.h        |  7 +++++++
>  arch/xtensa/include/asm/syscall.h     |  7 +++++++
>  include/asm-generic/syscall.h         | 14 ++++++++++++++
>  20 files changed, 144 insertions(+)
>
> diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
> index b3dd883699e7..1c0e349fd5c9 100644
> --- a/arch/s390/include/asm/syscall.h
> +++ b/arch/s390/include/asm/syscall.h
> @@ -24,6 +24,13 @@ static inline long syscall_get_nr(struct task_struct *task,
>  		(regs->int_code & 0xffff) : -1;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{

I think there should be a

	if (!test_pt_regs_flags(regs, PIF_SYSCALL))
		return;

before the modification so a user can't accidentally change int_code
when ptrace stopped in a non-syscall path.

> +	regs->int_code = (regs->int_code & ~0xffff) | (nr & 0xffff);
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {