[PATCH 2/2] powerpc: fix inconsistencies in syscall error return handling

Christophe Leroy christophe.leroy at csgroup.eu
Tue Jan 28 18:01:47 UTC 2025



Le 27/01/2025 à 19:14, Dmitry V. Levin a écrit :
> Since the introduction of SECCOMP_RET_TRACE support, the kernel supports
> simultaneously both the generic kernel -ERRORCODE return value ABI and
> the powerpc sc syscall return ABI for PTRACE_EVENT_SECCOMP tracers.
> This change is an attempt to address the code inconsistencies in syscall
> error return handling that were introduced as a side effect of the dual
> ABI support.
> 
> Signed-off-by: Dmitry V. Levin <ldv at strace.io>
> ---
>   arch/powerpc/kernel/ptrace/ptrace.c | 23 ++++++++++++++++++++---
>   arch/powerpc/kernel/signal.c        | 11 +++--------
>   arch/powerpc/kernel/syscall.c       |  6 +++---
>   3 files changed, 26 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
> index 727ed4a14545..3778775bf6ba 100644
> --- a/arch/powerpc/kernel/ptrace/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace/ptrace.c
> @@ -207,7 +207,7 @@ static int do_seccomp(struct pt_regs *regs)
>   	 * syscall parameter. This is different to the ptrace ABI where
>   	 * both r3 and orig_gpr3 contain the first syscall parameter.
>   	 */
> -	regs->gpr[3] = -ENOSYS;
> +	syscall_set_return_value(current, regs, -ENOSYS, 0);
>   
>   	/*
>   	 * We use the __ version here because we have already checked
> @@ -215,8 +215,18 @@ static int do_seccomp(struct pt_regs *regs)
>   	 * have already loaded -ENOSYS into r3, or seccomp has put
>   	 * something else in r3 (via SECCOMP_RET_ERRNO/TRACE).
>   	 */
> -	if (__secure_computing(NULL))
> +	if (__secure_computing(NULL)) {
> +
> +		/*
> +		 * Traditionally, both the generic kernel -ERRORCODE return
> +		 * value ABI and the powerpc sc syscall return ABI is
> +		 * supported.  For consistency, if the former is detected,
> +		 * convert it to the latter.
> +		 */
> +		if (!trap_is_scv(regs) && IS_ERR_VALUE(regs->gpr[3]))

Why !trap_is_scv(regs) ? Shouldn't this also work with scv allthough it 
should be a noop ?


> +			syscall_set_return_value(current, regs, regs->gpr[3], 0);
>   		return -1;
> +	}
>   
>   	/*
>   	 * The syscall was allowed by seccomp, restore the register
> @@ -226,6 +236,13 @@ static int do_seccomp(struct pt_regs *regs)
>   	 * allow the syscall to proceed.
>   	 */
>   	regs->gpr[3] = regs->orig_gpr3;
> +	if (!trap_is_scv(regs)) {
> +		/*
> +		 * Clear SO bit that was set in this function earlier by
> +		 * syscall_set_return_value.
> +		 */
> +		regs->ccr &= ~0x10000000L;
> +	}

Can't we use syscall_set_return_value() to do that ?

>   
>   	return 0;
>   }
> @@ -315,7 +332,7 @@ long do_syscall_trace_enter(struct pt_regs *regs)
>   	 * If we are aborting explicitly, or if the syscall number is
>   	 * now invalid, set the return value to -ENOSYS.
>   	 */
> -	regs->gpr[3] = -ENOSYS;
> +	syscall_set_return_value(current, regs, -ENOSYS, 0);
>   	return -1;
>   }
>   
> diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
> index aa17e62f3754..1a38d6bcaed6 100644
> --- a/arch/powerpc/kernel/signal.c
> +++ b/arch/powerpc/kernel/signal.c
> @@ -19,6 +19,7 @@
>   #include <asm/unistd.h>
>   #include <asm/debug.h>
>   #include <asm/tm.h>
> +#include <asm/syscall.h>
>   
>   #include "signal.h"
>   
> @@ -229,14 +230,8 @@ static void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
>   		regs_add_return_ip(regs, -4);
>   		regs->result = 0;
>   	} else {
> -		if (trap_is_scv(regs)) {
> -			regs->result = -EINTR;
> -			regs->gpr[3] = -EINTR;
> -		} else {
> -			regs->result = -EINTR;
> -			regs->gpr[3] = EINTR;
> -			regs->ccr |= 0x10000000;
> -		}
> +		regs->result = -EINTR;
> +		syscall_set_return_value(current, regs, -EINTR, 0);
>   	}
>   }
>   
> diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
> index be159ad4b77b..2fe47191e509 100644
> --- a/arch/powerpc/kernel/syscall.c
> +++ b/arch/powerpc/kernel/syscall.c
> @@ -122,7 +122,7 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0)
>   		if (unlikely(trap_is_unsupported_scv(regs))) {
>   			/* Unsupported scv vector */
>   			_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
> -			return regs->gpr[3];
> +			return regs_return_value(regs);
>   		}
>   		/*
>   		 * We use the return value of do_syscall_trace_enter() as the
> @@ -133,13 +133,13 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0)
>   		 */
>   		r0 = do_syscall_trace_enter(regs);
>   		if (unlikely(r0 >= NR_syscalls))
> -			return regs->gpr[3];
> +			return regs_return_value(regs);
>   
>   	} else if (unlikely(r0 >= NR_syscalls)) {
>   		if (unlikely(trap_is_unsupported_scv(regs))) {
>   			/* Unsupported scv vector */
>   			_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
> -			return regs->gpr[3];
> +			return regs_return_value(regs);
>   		}
>   		return -ENOSYS;
>   	}



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