Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH linux-next v10 5/7] powerpc: define syscall_get_error() | Date | Mon, 06 May 2019 23:17:12 +1000 |
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"Dmitry V. Levin" <ldv@altlinux.org> writes:
> syscall_get_error() is required to be implemented on this > architecture in addition to already implemented syscall_get_nr(), > syscall_get_arguments(), syscall_get_return_value(), and > syscall_get_arch() functions in order to extend the generic > ptrace API with PTRACE_GET_SYSCALL_INFO request. > > Cc: Michael Ellerman <mpe@ellerman.id.au> > Cc: Elvira Khabirova <lineprinter@altlinux.org> > Cc: Eugene Syromyatnikov <esyr@redhat.com> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > Cc: Paul Mackerras <paulus@samba.org> > Cc: Oleg Nesterov <oleg@redhat.com> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: linuxppc-dev@lists.ozlabs.org > Signed-off-by: Dmitry V. Levin <ldv@altlinux.org> > --- > > Michael, this patch is waiting for ACK since early December.
Sorry, the more I look at our seccomp/ptrace code the more problems I find :/
This change looks OK to me, given it will only be called by your new ptrace API.
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
> Notes: > v10: unchanged > v9: unchanged > v8: unchanged > v7: unchanged > v6: unchanged > v5: initial revision > > This change has been tested with > tools/testing/selftests/ptrace/get_syscall_info.c and strace, > so it's correct from PTRACE_GET_SYSCALL_INFO point of view. > > This cast doubts on commit v4.3-rc1~86^2~81 that changed > syscall_set_return_value() in a way that doesn't quite match > syscall_get_error(), but syscall_set_return_value() is out > of scope of this series, so I'll just let you know my concerns.
Yeah I think you're right. My commit made it work for seccomp but only on the basis that seccomp calls syscall_set_return_value() and then immediately goes out via the syscall exit path. And only the combination of those gets things into the same state that syscall_get_error() expects.
But with the way the code is currently structured if syscall_set_return_value() negated the error value, then the syscall exit path would then store the wrong thing in pt_regs->result. So I think it needs some more work rather than just reverting 1b1a3702a65c.
But I think fixing that can be orthogonal to this commit going in as the code does work as it's currently written, the in-between state that syscall_set_return_value() creates via seccomp should not be visible to ptrace.
cheers
> See also https://lore.kernel.org/lkml/874lbbt3k6.fsf@concordia.ellerman.id.au/ > for more details on powerpc syscall_set_return_value() confusion. > > arch/powerpc/include/asm/syscall.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h > index a048fed0722f..bd9663137d57 100644 > --- a/arch/powerpc/include/asm/syscall.h > +++ b/arch/powerpc/include/asm/syscall.h > @@ -38,6 +38,16 @@ static inline void syscall_rollback(struct task_struct *task, > regs->gpr[3] = regs->orig_gpr3; > } > > +static inline long syscall_get_error(struct task_struct *task, > + struct pt_regs *regs) > +{ > + /* > + * If the system call failed, > + * regs->gpr[3] contains a positive ERRORCODE. > + */ > + return (regs->ccr & 0x10000000UL) ? -regs->gpr[3] : 0; > +} > + > static inline long syscall_get_return_value(struct task_struct *task, > struct pt_regs *regs) > { > -- > ldv
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