On Wed, Feb 2, 2022 at 12:14 PM Heiko Carstens <hca@xxxxxxxxxxxxx> 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(?).
>
> For arm64 and riscv it seems that orig_x0 or orig_a0 respectively need to
> be added to user_pt_regs too, and the same fix like for s390 needs to be
> applied as well.
We just recently added syscall-specific macros to libbpf and fixed
this issue for x86-64. It would be great if people familiar with other
architectures contribute fixes for other architectures. Thanks!
