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

From: Jiaxun Yang
Date: Thu Apr 04 2024 - 11:08:14 EST

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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@xxxxxxxxxxx>
> Link: https://github.com/util-linux/util-linux/issues/2867
> Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>

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@xxxxxxxxxxx>

--
- Jiaxun

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