Naveen N. Rao wrote:
> Hi Heiko,
>
> Heiko Carstens wrote:
> > On Wed, Feb 02, 2022 at 12:41:58AM +0100, Ilya Leoshkevich wrote:
> > > user_pt_regs is used by eBPF in order to access userspace
> > > registers -
> > > see commit 466698e654e8 ("s390/bpf: correct broken uapi for
> > > BPF_PROG_TYPE_PERF_EVENT program type"). In order to access the
> > > first
> > > syscall argument from eBPF programs, we need to export
> > > orig_gpr2.
> > >
> > > Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> > > ---
> > > arch/s390/include/asm/ptrace.h | 2 +-
> > > arch/s390/include/uapi/asm/ptrace.h | 1 +
> > > 2 files changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/s390/include/asm/ptrace.h
> > > b/arch/s390/include/asm/ptrace.h
> > > index 4ffa8e7f0ed3..c8698e643904 100644
> > > --- a/arch/s390/include/asm/ptrace.h
> > > +++ b/arch/s390/include/asm/ptrace.h
> > > @@ -83,9 +83,9 @@ struct pt_regs {
> > > unsigned long args[1];
> > > psw_t psw;
> > > unsigned long gprs[NUM_GPRS];
> > > + unsigned long orig_gpr2;
> > > };
> > > };
> > > - unsigned long orig_gpr2;
> > > union {
> > > struct {
> > > unsigned int int_code;
> > > diff --git a/arch/s390/include/uapi/asm/ptrace.h
> > > b/arch/s390/include/uapi/asm/ptrace.h
> > > index ad64d673b5e6..b3dec603f507 100644
> > > --- a/arch/s390/include/uapi/asm/ptrace.h
> > > +++ b/arch/s390/include/uapi/asm/ptrace.h
> > > @@ -295,6 +295,7 @@ typedef struct {
> > > unsigned long args[1];
> > > psw_t psw;
> > > unsigned long gprs[NUM_GPRS];
> > > + unsigned long orig_gpr2;
> > > } user_pt_regs;
> >
> > Isn't this broken on nearly all architectures? I just checked
> > powerpc,
> > arm64, and riscv. While powerpc seems to mirror pt_regs as
> > user_pt_regs,
> > and therefore exports orig_gpr3, the bpf macros still seem to
> > access the
> > wrong location to access the first syscall parameter(?).
>
> On powerpc, gpr[3] continues to be valid on syscall entry (so this
> test
> passes on powerpc), though orig_gpr3 will remain valid throughout.
Hmm.. we can't use orig_gpr3 since we don't use a syscall wrapper.
All
system calls just receive the parameters directly.
- Naveen
