Subject: Re: [PATCH v2 4/7] syscall.h: introduce syscall_set_nr()

From: Charlie Jenkins <[email-masked]>
Date: Wed, 15 Jan 2025 18:20:05 -0800

On Mon, Jan 13, 2025 at 07:11:51PM +0200, Dmitry V. Levin wrote:
> 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 <[email-masked]>
> ---
>  arch/arc/include/asm/syscall.h        | 11 +++++++++++
>  arch/arm/include/asm/syscall.h        | 24 ++++++++++++++++++++++++
>  arch/arm64/include/asm/syscall.h      | 16 ++++++++++++++++
>  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       | 14 ++++++++++++++
>  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    | 10 ++++++++++
>  arch/riscv/include/asm/syscall.h      |  7 +++++++
>  arch/s390/include/asm/syscall.h       | 12 ++++++++++++
>  arch/sh/include/asm/syscall_32.h      | 12 ++++++++++++
>  arch/sparc/include/asm/syscall.h      | 12 ++++++++++++
>  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, 197 insertions(+)
> 
> diff --git a/arch/arc/include/asm/syscall.h b/arch/arc/include/asm/syscall.h
> index 89c1e1736356..728d625a10f1 100644
> --- a/arch/arc/include/asm/syscall.h
> +++ b/arch/arc/include/asm/syscall.h
> @@ -23,6 +23,17 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>  		return -1;
>  }
>  
> +static inline void
> +syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
> +{
> +	/*
> +	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
> +	 * the target task is stopped for tracing on entering syscall, so
> +	 * there is no need to have the same check syscall_get_nr() has.
> +	 */
> +	regs->r8 = nr;
> +}
> +
>  static inline void
>  syscall_rollback(struct task_struct *task, struct pt_regs *regs)
>  {
> diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h
> index 21927fa0ae2b..18b102a30741 100644
> --- a/arch/arm/include/asm/syscall.h
> +++ b/arch/arm/include/asm/syscall.h
> @@ -68,6 +68,30 @@ static inline void syscall_set_return_value(struct task_struct *task,
>  	regs->ARM_r0 = (long) error ? error : val;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	if (nr == -1) {
> +		task_thread_info(task)->abi_syscall = -1;
> +		/*
> +		 * When the syscall number is set to -1, the syscall will be
> +		 * skipped.  In this case the syscall return value has to be
> +		 * set explicitly, otherwise the first syscall argument is
> +		 * returned as the syscall return value.
> +		 */
> +		syscall_set_return_value(task, regs, -ENOSYS, 0);
> +		return;
> +	}
> +	if ((IS_ENABLED(CONFIG_AEABI) && !IS_ENABLED(CONFIG_OABI_COMPAT))) {
> +		task_thread_info(task)->abi_syscall = nr;
> +		return;
> +	}
> +	task_thread_info(task)->abi_syscall =
> +		(task_thread_info(task)->abi_syscall & ~__NR_SYSCALL_MASK) |
> +		(nr & __NR_SYSCALL_MASK);
> +}
> +
>  #define SYSCALL_MAX_ARGS 7
>  
>  static inline void syscall_get_arguments(struct task_struct *task,
> diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
> index 76020b66286b..712daa90e643 100644
> --- a/arch/arm64/include/asm/syscall.h
> +++ b/arch/arm64/include/asm/syscall.h
> @@ -61,6 +61,22 @@ static inline void syscall_set_return_value(struct task_struct *task,
>  	regs->regs[0] = val;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->syscallno = nr;
> +	if (nr == -1) {
> +		/*
> +		 * When the syscall number is set to -1, the syscall will be
> +		 * skipped.  In this case the syscall return value has to be
> +		 * set explicitly, otherwise the first syscall argument is
> +		 * returned as the syscall return value.
> +		 */
> +		syscall_set_return_value(task, regs, -ENOSYS, 0);
> +	}
> +}
> +
>  #define SYSCALL_MAX_ARGS 6
>  
>  static inline void syscall_get_arguments(struct task_struct *task,
> diff --git a/arch/hexagon/include/asm/syscall.h b/arch/hexagon/include/asm/syscall.h
> index 1024a6548d78..70637261817a 100644
> --- a/arch/hexagon/include/asm/syscall.h
> +++ b/arch/hexagon/include/asm/syscall.h
> @@ -26,6 +26,13 @@ static inline long syscall_get_nr(struct task_struct *task,
>  	return regs->r06;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->r06 = nr;
> +}
> +
>  static inline void syscall_get_arguments(struct task_struct *task,
>  					 struct pt_regs *regs,
>  					 unsigned long *args)
> diff --git a/arch/loongarch/include/asm/syscall.h b/arch/loongarch/include/asm/syscall.h
> index ff415b3c0a8e..81d2733f7b94 100644
> --- a/arch/loongarch/include/asm/syscall.h
> +++ b/arch/loongarch/include/asm/syscall.h
> @@ -26,6 +26,13 @@ static inline long syscall_get_nr(struct task_struct *task,
>  	return regs->regs[11];
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->regs[11] = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/m68k/include/asm/syscall.h b/arch/m68k/include/asm/syscall.h
> index d1453e850cdd..bf84b160c2eb 100644
> --- a/arch/m68k/include/asm/syscall.h
> +++ b/arch/m68k/include/asm/syscall.h
> @@ -14,6 +14,13 @@ static inline int syscall_get_nr(struct task_struct *task,
>  	return regs->orig_d0;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->orig_d0 = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/microblaze/include/asm/syscall.h b/arch/microblaze/include/asm/syscall.h
> index 5eb3f624cc59..b5b6b91fae3e 100644
> --- a/arch/microblaze/include/asm/syscall.h
> +++ b/arch/microblaze/include/asm/syscall.h
> @@ -14,6 +14,13 @@ static inline long syscall_get_nr(struct task_struct *task,
>  	return regs->r12;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->r12 = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
> index 3163d1506fae..58d68205fd2c 100644
> --- a/arch/mips/include/asm/syscall.h
> +++ b/arch/mips/include/asm/syscall.h
> @@ -41,6 +41,20 @@ static inline long syscall_get_nr(struct task_struct *task,
>  	return task_thread_info(task)->syscall;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	/*
> +	 * New syscall number has to be assigned to regs[2] because
> +	 * syscall_trace_entry() loads it from there unconditionally.
> +	 *
> +	 * Consequently, if the syscall was indirect and nr != __NR_syscall,
> +	 * then after this assignment the syscall will cease to be indirect.
> +	 */
> +	task_thread_info(task)->syscall = regs->regs[2] = nr;
> +}
> +
>  static inline void mips_syscall_update_nr(struct task_struct *task,
>  					  struct pt_regs *regs)
>  {
> diff --git a/arch/nios2/include/asm/syscall.h b/arch/nios2/include/asm/syscall.h
> index 526449edd768..8e3eb1d689bb 100644
> --- a/arch/nios2/include/asm/syscall.h
> +++ b/arch/nios2/include/asm/syscall.h
> @@ -15,6 +15,11 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>  	return regs->r2;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
> +{
> +	regs->r2 = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				struct pt_regs *regs)
>  {
> diff --git a/arch/openrisc/include/asm/syscall.h b/arch/openrisc/include/asm/syscall.h
> index e6383be2a195..5e037d9659c5 100644
> --- a/arch/openrisc/include/asm/syscall.h
> +++ b/arch/openrisc/include/asm/syscall.h
> @@ -25,6 +25,12 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>  	return regs->orig_gpr11;
>  }
>  
> +static inline void
> +syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
> +{
> +	regs->orig_gpr11 = nr;
> +}
> +
>  static inline void
>  syscall_rollback(struct task_struct *task, struct pt_regs *regs)
>  {
> diff --git a/arch/parisc/include/asm/syscall.h b/arch/parisc/include/asm/syscall.h
> index b146d0ae4c77..c11222798ab2 100644
> --- a/arch/parisc/include/asm/syscall.h
> +++ b/arch/parisc/include/asm/syscall.h
> @@ -17,6 +17,13 @@ static inline long syscall_get_nr(struct task_struct *tsk,
>  	return regs->gr[20];
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *tsk,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->gr[20] = nr;
> +}
> +
>  static inline void syscall_get_arguments(struct task_struct *tsk,
>  					 struct pt_regs *regs,
>  					 unsigned long *args)
> diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
> index 521f279e6b33..7505dcfed247 100644
> --- a/arch/powerpc/include/asm/syscall.h
> +++ b/arch/powerpc/include/asm/syscall.h
> @@ -39,6 +39,16 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>  		return -1;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
> +{
> +	/*
> +	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
> +	 * the target task is stopped for tracing on entering syscall, so
> +	 * there is no need to have the same check syscall_get_nr() has.
> +	 */
> +	regs->gpr[0] = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
> index 8d389ba995c8..a5281cdf2b10 100644
> --- a/arch/riscv/include/asm/syscall.h
> +++ b/arch/riscv/include/asm/syscall.h
> @@ -30,6 +30,13 @@ static inline int syscall_get_nr(struct task_struct *task,
>  	return regs->a7;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->a7 = nr;
> +}

Looks good for riscv.

Tested-by: Charlie Jenkins <[email-masked]>
Reviewed-by: Charlie Jenkins <[email-masked]>

> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
> index b3dd883699e7..12cd0c60c07b 100644
> --- a/arch/s390/include/asm/syscall.h
> +++ b/arch/s390/include/asm/syscall.h
> @@ -24,6 +24,18 @@ 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)
> +{
> +	/*
> +	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
> +	 * the target task is stopped for tracing on entering syscall, so
> +	 * there is no need to have the same check syscall_get_nr() has.
> +	 */
> +	regs->int_code = (regs->int_code & ~0xffff) | (nr & 0xffff);
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/sh/include/asm/syscall_32.h b/arch/sh/include/asm/syscall_32.h
> index cb51a7528384..7027d87d901d 100644
> --- a/arch/sh/include/asm/syscall_32.h
> +++ b/arch/sh/include/asm/syscall_32.h
> @@ -15,6 +15,18 @@ static inline long syscall_get_nr(struct task_struct *task,
>  	return (regs->tra >= 0) ? regs->regs[3] : -1L;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	/*
> +	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
> +	 * the target task is stopped for tracing on entering syscall, so
> +	 * there is no need to have the same check syscall_get_nr() has.
> +	 */
> +	regs->regs[3] = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/sparc/include/asm/syscall.h b/arch/sparc/include/asm/syscall.h
> index 62a5a78804c4..b0233924d323 100644
> --- a/arch/sparc/include/asm/syscall.h
> +++ b/arch/sparc/include/asm/syscall.h
> @@ -25,6 +25,18 @@ static inline long syscall_get_nr(struct task_struct *task,
>  	return (syscall_p ? regs->u_regs[UREG_G1] : -1L);
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	/*
> +	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
> +	 * the target task is stopped for tracing on entering syscall, so
> +	 * there is no need to have the same check syscall_get_nr() has.
> +	 */
> +	regs->u_regs[UREG_G1] = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/um/include/asm/syscall-generic.h b/arch/um/include/asm/syscall-generic.h
> index 2984feb9d576..bcd73bcfe577 100644
> --- a/arch/um/include/asm/syscall-generic.h
> +++ b/arch/um/include/asm/syscall-generic.h
> @@ -21,6 +21,11 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>  	return PT_REGS_SYSCALL_NR(regs);
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
> +{
> +	PT_REGS_SYSCALL_NR(regs) = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
> index b9c249dd9e3d..c10dbb74cd00 100644
> --- a/arch/x86/include/asm/syscall.h
> +++ b/arch/x86/include/asm/syscall.h
> @@ -38,6 +38,13 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>  	return regs->orig_ax;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->orig_ax = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/arch/xtensa/include/asm/syscall.h b/arch/xtensa/include/asm/syscall.h
> index f9a671cbf933..7db3b489c8ad 100644
> --- a/arch/xtensa/include/asm/syscall.h
> +++ b/arch/xtensa/include/asm/syscall.h
> @@ -28,6 +28,13 @@ static inline long syscall_get_nr(struct task_struct *task,
>  	return regs->syscall;
>  }
>  
> +static inline void syscall_set_nr(struct task_struct *task,
> +				  struct pt_regs *regs,
> +				  int nr)
> +{
> +	regs->syscall = nr;
> +}
> +
>  static inline void syscall_rollback(struct task_struct *task,
>  				    struct pt_regs *regs)
>  {
> diff --git a/include/asm-generic/syscall.h b/include/asm-generic/syscall.h
> index 0f7b9a493de7..e33fd4e783c1 100644
> --- a/include/asm-generic/syscall.h
> +++ b/include/asm-generic/syscall.h
> @@ -37,6 +37,20 @@ struct pt_regs;
>   */
>  int syscall_get_nr(struct task_struct *task, struct pt_regs *regs);
>  
> +/**
> + * syscall_set_nr - change the system call a task is executing
> + * @task:	task of interest, must be blocked
> + * @regs:	task_pt_regs() of @task
> + * @nr:		system call number
> + *
> + * Changes the system call number @task is about to execute.
> + *
> + * It's only valid to call this when @task is stopped for tracing on
> + * entry to a system call, due to %SYSCALL_WORK_SYSCALL_TRACE or
> + * %SYSCALL_WORK_SYSCALL_AUDIT.
> + */
> +void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr);
> +
>  /**
>   * syscall_rollback - roll back registers after an aborted system call
>   * @task:	task of interest, must be in system call exit tracing
> -- 
> ldv