Re: [PATCH] MIPS: scall: Save thread_info.syscall unconditionally on entry

["Jiaxun Yang" <jiaxun.yang@flygoat.com>]

在2024年3月28日三月 下午2:27，Jiaxun Yang写道：
> thread_info.syscall is used by syscall_get_nr to supply syscall nr
> over a thread stack frame.
>
> Previously, thread_info.syscall is only saved at syscall_trace_enter
> when syscall tracing is enabled. However rest of the kernel code do
> expect syscall_get_nr to be available without syscall tracing. The
> previous design breaks collect_syscall.
>
> Move saving process to syscall entry to fix it.
>
> Reported-by: Xi Ruoyao <xry111@xry111.site>
> Link: https://github.com/util-linux/util-linux/issues/2867
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

Ping, this needs to be in fixes tree.

Thanks

> ---
>  arch/mips/include/asm/ptrace.h |  2 +-
>  arch/mips/kernel/asm-offsets.c |  1 +
>  arch/mips/kernel/ptrace.c      | 15 ++++++---------
>  arch/mips/kernel/scall32-o32.S | 23 +++++++++++++----------
>  arch/mips/kernel/scall64-n32.S |  3 ++-
>  arch/mips/kernel/scall64-n64.S |  3 ++-
>  arch/mips/kernel/scall64-o32.S | 33 +++++++++++++++++----------------
>  7 files changed, 42 insertions(+), 38 deletions(-)
>
> diff --git a/arch/mips/include/asm/ptrace.h b/arch/mips/include/asm/ptrace.h
> index d14d0e37ad02..4a2b40ce39e0 100644
> --- a/arch/mips/include/asm/ptrace.h
> +++ b/arch/mips/include/asm/ptrace.h
> @@ -159,7 +159,7 @@ extern unsigned long exception_ip(struct pt_regs *regs);
>  #define exception_ip(regs) exception_ip(regs)
>  #define profile_pc(regs) instruction_pointer(regs)
> 
> -extern asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall);
> +extern asmlinkage long syscall_trace_enter(struct pt_regs *regs);
>  extern asmlinkage void syscall_trace_leave(struct pt_regs *regs);
> 
>  extern void die(const char *, struct pt_regs *) __noreturn;
> diff --git a/arch/mips/kernel/asm-offsets.c 
> b/arch/mips/kernel/asm-offsets.c
> index d1b11f66f748..cb1045ebab06 100644
> --- a/arch/mips/kernel/asm-offsets.c
> +++ b/arch/mips/kernel/asm-offsets.c
> @@ -101,6 +101,7 @@ void output_thread_info_defines(void)
>  	OFFSET(TI_CPU, thread_info, cpu);
>  	OFFSET(TI_PRE_COUNT, thread_info, preempt_count);
>  	OFFSET(TI_REGS, thread_info, regs);
> +	OFFSET(TI_SYSCALL, thread_info, syscall);
>  	DEFINE(_THREAD_SIZE, THREAD_SIZE);
>  	DEFINE(_THREAD_MASK, THREAD_MASK);
>  	DEFINE(_IRQ_STACK_SIZE, IRQ_STACK_SIZE);
> diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
> index 59288c13b581..61503a36067e 100644
> --- a/arch/mips/kernel/ptrace.c
> +++ b/arch/mips/kernel/ptrace.c
> @@ -1317,16 +1317,13 @@ long arch_ptrace(struct task_struct *child, 
> long request,
>   * Notification of system call entry/exit
>   * - triggered by current->work.syscall_trace
>   */
> -asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall)
> +asmlinkage long syscall_trace_enter(struct pt_regs *regs)
>  {
>  	user_exit();
> 
> -	current_thread_info()->syscall = syscall;
> -
>  	if (test_thread_flag(TIF_SYSCALL_TRACE)) {
>  		if (ptrace_report_syscall_entry(regs))
>  			return -1;
> -		syscall = current_thread_info()->syscall;
>  	}
> 
>  #ifdef CONFIG_SECCOMP
> @@ -1335,7 +1332,7 @@ asmlinkage long syscall_trace_enter(struct 
> pt_regs *regs, long syscall)
>  		struct seccomp_data sd;
>  		unsigned long args[6];
> 
> -		sd.nr = syscall;
> +		sd.nr = current_thread_info()->syscall;
>  		sd.arch = syscall_get_arch(current);
>  		syscall_get_arguments(current, regs, args);
>  		for (i = 0; i < 6; i++)
> @@ -1345,23 +1342,23 @@ asmlinkage long syscall_trace_enter(struct 
> pt_regs *regs, long syscall)
>  		ret = __secure_computing(&sd);
>  		if (ret == -1)
>  			return ret;
> -		syscall = current_thread_info()->syscall;
>  	}
>  #endif
> 
>  	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
>  		trace_sys_enter(regs, regs->regs[2]);
> 
> -	audit_syscall_entry(syscall, regs->regs[4], regs->regs[5],
> +	audit_syscall_entry(current_thread_info()->syscall,
> +			    regs->regs[4], regs->regs[5],
>  			    regs->regs[6], regs->regs[7]);
> 
>  	/*
>  	 * Negative syscall numbers are mistaken for rejected syscalls, but
>  	 * won't have had the return value set appropriately, so we do so now.
>  	 */
> -	if (syscall < 0)
> +	if (current_thread_info()->syscall < 0)
>  		syscall_set_return_value(current, regs, -ENOSYS, 0);
> -	return syscall;
> +	return current_thread_info()->syscall;
>  }
> 
>  /*
> diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S
> index 18dc9b345056..2c604717e630 100644
> --- a/arch/mips/kernel/scall32-o32.S
> +++ b/arch/mips/kernel/scall32-o32.S
> @@ -77,6 +77,18 @@ loads_done:
>  	PTR_WD	load_a7, bad_stack_a7
>  	.previous
> 
> +	/*
> +	 * syscall number is in v0 unless we called syscall(__NR_###)
> +	 * where the real syscall number is in a0
> +	 */
> +	subu	t2, v0,  __NR_O32_Linux
> +	bnez	t2, 1f /* __NR_syscall at offset 0 */
> +	LONG_S	a0, TI_SYSCALL($28)	# Save a0 as syscall number
> +	b	2f
> +1:
> +	LONG_S	v0, TI_SYSCALL($28)	# Save v0 as syscall number
> +2:
> +
>  	lw	t0, TI_FLAGS($28)	# syscall tracing enabled?
>  	li	t1, _TIF_WORK_SYSCALL_ENTRY
>  	and	t0, t1
> @@ -114,16 +126,7 @@ syscall_trace_entry:
>  	SAVE_STATIC
>  	move	a0, sp
> 
> -	/*
> -	 * syscall number is in v0 unless we called syscall(__NR_###)
> -	 * where the real syscall number is in a0
> -	 */
> -	move	a1, v0
> -	subu	t2, v0,  __NR_O32_Linux
> -	bnez	t2, 1f /* __NR_syscall at offset 0 */
> -	lw	a1, PT_R4(sp)
> -
> -1:	jal	syscall_trace_enter
> +	jal	syscall_trace_enter
> 
>  	bltz	v0, 1f			# seccomp failed? Skip syscall
> 
> diff --git a/arch/mips/kernel/scall64-n32.S b/arch/mips/kernel/scall64-n32.S
> index 97456b2ca7dc..97788859238c 100644
> --- a/arch/mips/kernel/scall64-n32.S
> +++ b/arch/mips/kernel/scall64-n32.S
> @@ -44,6 +44,8 @@ NESTED(handle_sysn32, PT_SIZE, sp)
> 
>  	sd	a3, PT_R26(sp)		# save a3 for syscall restarting
> 
> +	LONG_S	v0, TI_SYSCALL($28)     # Store syscall number
> +
>  	li	t1, _TIF_WORK_SYSCALL_ENTRY
>  	LONG_L	t0, TI_FLAGS($28)	# syscall tracing enabled?
>  	and	t0, t1, t0
> @@ -72,7 +74,6 @@ syscall_common:
>  n32_syscall_trace_entry:
>  	SAVE_STATIC
>  	move	a0, sp
> -	move	a1, v0
>  	jal	syscall_trace_enter
> 
>  	bltz	v0, 1f			# seccomp failed? Skip syscall
> diff --git a/arch/mips/kernel/scall64-n64.S b/arch/mips/kernel/scall64-n64.S
> index e6264aa62e45..be11ea5cc67e 100644
> --- a/arch/mips/kernel/scall64-n64.S
> +++ b/arch/mips/kernel/scall64-n64.S
> @@ -46,6 +46,8 @@ NESTED(handle_sys64, PT_SIZE, sp)
> 
>  	sd	a3, PT_R26(sp)		# save a3 for syscall restarting
> 
> +	LONG_S	v0, TI_SYSCALL($28)     # Store syscall number
> +
>  	li	t1, _TIF_WORK_SYSCALL_ENTRY
>  	LONG_L	t0, TI_FLAGS($28)	# syscall tracing enabled?
>  	and	t0, t1, t0
> @@ -82,7 +84,6 @@ n64_syscall_exit:
>  syscall_trace_entry:
>  	SAVE_STATIC
>  	move	a0, sp
> -	move	a1, v0
>  	jal	syscall_trace_enter
> 
>  	bltz	v0, 1f			# seccomp failed? Skip syscall
> diff --git a/arch/mips/kernel/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
> index d3c2616cba22..7a5abb73e531 100644
> --- a/arch/mips/kernel/scall64-o32.S
> +++ b/arch/mips/kernel/scall64-o32.S
> @@ -79,6 +79,22 @@ loads_done:
>  	PTR_WD	load_a7, bad_stack_a7
>  	.previous
> 
> +	/*
> +	 * absolute syscall number is in v0 unless we called syscall(__NR_###)
> +	 * where the real syscall number is in a0
> +	 * note: NR_syscall is the first O32 syscall but the macro is
> +	 * only defined when compiling with -mabi=32 (CONFIG_32BIT)
> +	 * therefore __NR_O32_Linux is used (4000)
> +	 */
> +
> +	subu	t2, v0,  __NR_O32_Linux
> +	bnez	t2, 1f /* __NR_syscall at offset 0 */
> +	LONG_S	a0, TI_SYSCALL($28)	# Save a0 as syscall number
> +	b	2f
> +1:
> +	LONG_S	v0, TI_SYSCALL($28)	# Save v0 as syscall number
> +2:
> +
>  	li	t1, _TIF_WORK_SYSCALL_ENTRY
>  	LONG_L	t0, TI_FLAGS($28)	# syscall tracing enabled?
>  	and	t0, t1, t0
> @@ -113,22 +129,7 @@ trace_a_syscall:
>  	sd	a7, PT_R11(sp)		# For indirect syscalls
> 
>  	move	a0, sp
> -	/*
> -	 * absolute syscall number is in v0 unless we called syscall(__NR_###)
> -	 * where the real syscall number is in a0
> -	 * note: NR_syscall is the first O32 syscall but the macro is
> -	 * only defined when compiling with -mabi=32 (CONFIG_32BIT)
> -	 * therefore __NR_O32_Linux is used (4000)
> -	 */
> -	.set	push
> -	.set	reorder
> -	subu	t1, v0,  __NR_O32_Linux
> -	move	a1, v0
> -	bnez	t1, 1f /* __NR_syscall at offset 0 */
> -	ld	a1, PT_R4(sp) /* Arg1 for __NR_syscall case */
> -	.set	pop
> -
> -1:	jal	syscall_trace_enter
> +	jal	syscall_trace_enter
> 
>  	bltz	v0, 1f			# seccomp failed? Skip syscall
> 
>
> ---
> base-commit: a6bd6c9333397f5a0e2667d4d82fef8c970108f2
> change-id: 20240328-mips_save_syscall-be471311cc9b
>
> Best regards,
> -- 
> Jiaxun Yang <jiaxun.yang@flygoat.com>

-- 
- Jiaxun